Insects (from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

') are pancrustacean hexapod

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s of the class Insecta. They are the largest group within the

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

phylum. Insects have a chitinous

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...

, a three-part body ( head,

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

and

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...

), three pairs of jointed legs,

compound eye A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which disti ...

s and one pair of antennae. Their blood is not totally contained in vessels; some circulates in an open cavity known as the haemocoel. Insects are the most diverse group of animals; they include more than a million described

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

and represent more than half of all known living

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

s. The total number of extant species is estimated at between six and ten million; In: potentially over 90% of the animal life forms on Earth are insects. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group,

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s, which recent research has indicated insects are nested within. Nearly all insects hatch from

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s. Insect growth is constrained by the inelastic

and development involves a series of molts. The immature stages often differ from the adults in structure, habit and habitat, and can include a usually immobile

pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in thei ...

l stage in those groups that undergo four-stage metamorphosis. Insects that undergo three-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages."insect physiology" ''McGraw-Hill Encyclopedia of Science and Technology'', Ch. 9, p. 233, 2007 The higher level relationship of the

insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

is unclear. Fossilized insects of enormous size have been found from the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

Era, including giant dragonflies with wingspans of . The most diverse insect groups appear to have

coevolved In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...

with

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s. Adult insects typically move about by walking, flying, or sometimes swimming. As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, composed of the front and rear on one side with the middle on the other side. Insects are the only invertebrate group with members able to achieve sustained powered flight, and all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

l adaptations that include

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s, and some adult insects are aquatic and have adaptations for swimming. Some species, such as

water striders The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, or water skimmers. Consistent with the classification of the Gerridae as tr ...

, are capable of walking on the surface of water. Insects are mostly solitary, but some, such as certain bees,

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...

s and

termite Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blatto ...

s, are social and live in large, well-organized colonies. Some insects, such as

earwig Earwigs make up the insect order Dermaptera. With about 2,000 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forcep-like pincers on their abdomen, and membranous wings folde ...

s, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male

moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...

s can sense the

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s of female moths over great distances. Other species communicate with sounds:

crickets Crickets are orthopteran insects which are related to bush crickets, and, more distantly, to grasshoppers. In older literature, such as Imms,Imms AD, rev. Richards OW & Davies RG (1970) ''A General Textbook of Entomology'' 9th Ed. Methuen 8 ...

stridulate, or rub their wings together, to attract a mate and repel other males. Lampyrid

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s communicate with light. Humans regard certain insects as pests, and attempt to control them using insecticides, and a host of other techniques. Some insects damage crops by feeding on sap, leaves, fruits, or wood. Some species are

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

, and may

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

diseases. Some insects perform complex ecological roles;

blow-flies The Calliphoridae (commonly known as blow flies, blow-flies, carrion flies, bluebottles, greenbottles, or cluster flies) are a family of insects in the order Diptera, with almost 1,900 known species. The maggot larvae, often used as fishing ba ...

, for example, help consume carrion but also spread diseases. Insect

pollinators A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insects are the maj ...

are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least partly dependent; without them, the terrestrial portion of the biosphere would be devastated. Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce

silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the ...

and honey bees produce

honey Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...

and both have been domesticated by humans. Insects are consumed as food in 80% of the world's nations, by people in roughly 3000 ethnic groups. Human activities also have effects on insect biodiversity.

Etymology

The word ''insect'' comes from the

word , meaning "with a notched or divided body", or literally "cut into", from the neuter singular perfect passive participle of , "to cut into, to cut up", from "into" and from "to cut"; because insects appear "cut into" three sections. The Latin word was introduced by

Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ' ...

who

calque In linguistics, a calque () or loan translation is a word or phrase borrowed from another language by literal word-for-word or root-for-root translation. When used as a verb, "to calque" means to borrow a word or phrase from another language w ...

d the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...

word ''éntomon'' "insect" (as in entomology) from ''éntomos'' "cut into sections" or "cut in pieces"; ''éntomon'' was

Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...

's term for this class of life, also in reference to their "notched" bodies. The English word ''insect'' first appears documented in 1601 in

Holland Holland is a geographical regionG. Geerts & H. Heestermans, 1981, ''Groot Woordenboek der Nederlandse Taal. Deel I'', Van Dale Lexicografie, Utrecht, p 1105 and former province on the western coast of the Netherlands. From the 10th to the 16th c ...

's translation of Pliny. Translations of Aristotle's term also form the usual word for ''insect'' in Welsh (, from "to cut" and , "animal"),

Serbo-Croatian Serbo-Croatian () – also called Serbo-Croat (), Serbo-Croat-Bosnian (SCB), Bosnian-Croatian-Serbian (BCS), and Bosnian-Croatian-Montenegrin-Serbian (BCMS) – is a South Slavic language and the primary language of Serbia, Croatia, Bosnia an ...

(, from , "to cut"),

Russian Russian(s) refers to anything related to Russia, including: *Russians (, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *Rossiyane (), Russian language term for all citizens and peo ...

( [], from , "to cut"), etc. In common parlance, insects are also called bugs, though this term usually includes all terrestrial arthropods. The term is also occasionally extended to colloquial names for freshwater or marine crustaceans (e.g.

Balmain bug Balmain may refer to: Places * Balmain, New South Wales, a suburb of Sydney, Australia * Electoral district of Balmain, an electoral division in New South Wales, Australia * Balmain East, New South Wales, a suburb of Sydney, Australia * Balmain Ho ...

Moreton Bay bug ''Thenus orientalis'' is a species of slipper lobster from the Indian and Pacific oceans. ''T. orientalis'' is known by a number of common names. The United Nations Food and Agriculture Organization prefers the name flathead lobster, while t ...

, mudbug) and used by physicians and bacteriologists for disease-causing germs (e.g. superbugs), but entomologists to some extent reserve this term for a narrow category of "

true bugs Hemiptera (; ) is an order (biology), order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, Reduviidae, assassin bugs, Cimex, bed bugs, and shield bugs. ...

", insects of the order Hemiptera, such as cicadas and shield bugs.

Definitions

The precise definition of the taxon Insecta and the equivalent English name "insect" varies; three alternative definitions are shown in the table. In the broadest

circumscription Circumscription may refer to: *Circumscribed circle * Circumscription (logic) *Circumscription (taxonomy) *Circumscription theory, a theory about the origins of the political state in the history of human evolution proposed by the American anthrop ...

, Insecta ''

sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...

'' consists of all hexapods. Traditionally, insects defined in this way were divided into "Apterygota" (the first five groups in the table)—the wingless insects—and

Pterygota The Pterygota ( grc, πτερυγωτός, pterugōtós, winged) are a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless (that is, insect groups whose ancestors once had wings b ...

—the winged and secondarily wingless insects. However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic, and so does not form a good taxon. A narrower circumscription restricts insects to those hexapods with external mouthparts, and comprises only the last three groups in the table. In this sense, Insecta '' sensu stricto'' is equivalent to Ectognatha. In the narrowest circumscription, insects are restricted to hexapods that are either winged or descended from winged ancestors. Insecta '' sensu strictissimo'' is then equivalent to Pterygota., pp. 29–30 For the purposes of this article, the middle definition is used; insects consist of two wingless taxa,

Archaeognatha The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the ...

(jumping bristletails) and

Zygentoma Zygentoma are an order in the class Insecta, and consist of about 550 known species. The Zygentoma include the so-called silverfish or fishmoths, and the firebrats. A conspicuous feature of the order are the three long caudal filaments. The t ...

(silverfish), plus the winged or secondarily wingless Pterygota.

Phylogeny and evolution

External phylogeny

Although traditionally grouped with

millipede Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a resu ...

s and centipedes, more recent analysis indicates closer evolutionary ties with

s. In the Pancrustacea theory, insects, together with

Entognatha The Entognatha are a class of wingless and ametabolous arthropods, which, together with the insects, makes up the subphylum Hexapoda. Their mouthparts are entognathous, meaning that they are retracted within the head, unlike the insects. Entog ...

Remipedia Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The ...

, and

Cephalocarida The Cephalocarida are a class in the subphylum Crustacea comprising only 12 benthic species. They were discovered in 1955 by Howard L. Sanders, and are commonly referred to as horseshoe shrimp. They have been grouped together with the Remipedi ...

, form a clade, the Pancrustacea. Insects form a single clade, closely related to crustaceans and

myriapod Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian, ...

s. Other terrestrial arthropods, such as centipedes,

scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always en ...

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

woodlice A woodlouse (plural woodlice) is an isopod crustacean from the polyphyleticThe current consensus is that Oniscidea is actually triphyletic suborder Oniscidea within the order Isopoda. They get their name from often being found in old wood ...

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...

s, and

tick Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...

s are sometimes confused with insects since their body plans can appear similar, sharing (as do all arthropods) a jointed exoskeleton. However, upon closer examination, their features differ significantly; most noticeably, they do not have the six-legged characteristic of adult insects. A

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

tree of the arthropods places the insects in the context of other hexapods and the crustaceans, and the more distantly-related myriapods and chelicerates. Insect antennae comparison

Four large-scale radiations of insects have occurred:

s (from about 300 million years ago),

flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced m ...

(from about 250 million years ago),

s and

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...

s (both from about 150 million years ago). These four groups account for the majority of described species. The origins of

insect flight Insects are the only group of invertebrates that have evolved wings and flight. Insects first flew in the Carboniferous, some 350 to 400 million years ago, making them the first animals to evolve flight. Wings may have evolved from appenda ...

remain obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects had an additional pair of winglets attaching to the first segment of the thorax, for a total of three pairs. As of 2009, no evidence suggests the insects were a particularly successful group of animals before they evolved to have wings.

Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

and Early Permian insect orders include both extant groups, their stem groups, and a number of

groups, now extinct. During this era, some giant dragonfly-like forms reached wingspans of , making them far larger than any living insect. This gigantism may have been due to higher

atmospheric oxygen Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary approach of research and draws on environmental chemistry, physics, meteorol ...

levels that allowed increased respiratory efficiency relative to today. The lack of flying vertebrates could have been another factor. Most extinct orders of insects developed during the Permian period that began around 270 million years ago. Many of the early groups became extinct during the Permian-Triassic extinction event, the largest mass extinction in the history of the Earth, around 252 million years ago. In 2008, researchers at

Tufts University Tufts University is a private research university on the border of Medford and Somerville, Massachusetts. It was founded in 1852 as Tufts College by Christian universalists who sought to provide a nonsectarian institution of higher learning. ...

uncovered what they believe is the world's oldest known full-body impression of a primitive flying insect, a 300-million-year-old specimen from the

Carboniferous period The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

. The oldest insect fossil was considered to be the Devonian '' Rhyniognatha hirsti'', from the 396-million-year-old

Rhynie chert The Rhynie chert is a Lower Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte). It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is locate ...

. However, other analyses have disputed this placement, finding it to be more likely a myriapod. The remarkably successful Hymenoptera (wasps, bees, and ants) appeared as long as 200 million years ago in the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

period, but achieved their wide diversity more recently in the Cenozoic era, which began 66 million years ago. Some highly successful insect groups evolved in conjunction with

s, a powerful illustration of coevolution.

Internal phylogeny

The internal phylogeny is based on the works of Sroka, Staniczek & Bechly 2014, Prokop et al. 2017 and Wipfler et al. 2019.

Taxonomy

Traditional morphology-based or appearance-based systematics have usually given the

Hexapoda The subphylum Hexapoda (from Greek for 'six legs') comprises most species of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura (all of these were once considered ins ...

the rank of superclass, and identified four groups within it: insects (Ectognatha), springtails (

Collembola Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...

Protura The Protura, or proturans, and sometimes nicknamed coneheads, are very small (0.6-1.5mm long), soil-dwelling animals, so inconspicuous they were not noticed until the 20th century. The Protura constitute an order of hexapods that were previously ...

, and

Diplura The order Diplura ("two-pronged bristletails") is one of three orders of non-insect hexapods within the class Entognatha (alongside Collembola (springtails) and Protura). The name "diplura", or "two tails", refers to the characteristic pair of ...

, the latter three being grouped together as the

on the basis of internalized mouth parts. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A recent theory is that the Hexapoda are

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

(where the last common ancestor was not a member of the group), with the entognath classes having separate evolutionary histories from the Insecta. Many of the traditional appearance-based

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

are paraphyletic, so rather than using ranks like subclass, superorder, and

infraorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

, it has proved better to use monophyletic groupings (in which the last common ancestor is a member of the group). The following represents the best-supported monophyletic groupings for the Insecta. Insects can be divided into two groups historically treated as subclasses: wingless insects, known as Apterygota, and winged insects, known as Pterygota. The Apterygota consisted of the primitively wingless orders Archaeognatha (jumping bristletails) and Zygentoma (silverfish). However, Apterygota is not a monophyletic group, as Archaeognatha are the sister group to all other insects, based on the arrangement of their

mandibles In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, while Zygentoma and Pterygota are grouped together as Dicondylia. It was originally believed that Archaeognatha possessed a single phylogenetically primitive

condyle A condyle (;Entry "condyle"
in
derived insects have two, but this has since been shown to be incorrect; all insects, including Archaeognatha, have dicondylic mandibles, but archaeognaths possess two articulations that are homologous to those in other insects, though slightly different.Blanke, A., Machida, R., Szucsich, N.U., Wilde, F. and Misof, B. (2015) Mandibles with two joints evolved much earlier in the history of insects: dicondyly is a synapomorphy of bristletails, silverfish and winged insects. ''Syst. Entomol.'' 40: 357-364. https://doi.org/10.1111/syen.12107 The Zygentoma themselves possibly are not monophyletic, with the family

Lepidotrichidae Lepidotrichidae is a family of basal insects belonging to the order Zygentoma ( silverfish and allies) The family contains the extinct '' Lepidotrix'', known from specimens preserved in Eocene The Eocene ( ) Epoch is a geological epoch tha ...

being a sister group to the Dicondylia (Pterygota and the remaining Zygentoma). Paleoptera and Neoptera are the winged orders of insects differentiated by the presence of hardened body parts called

sclerite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

s, and in the Neoptera, muscles that allow their wings to fold flatly over the abdomen. Neoptera can further be divided into incomplete metamorphosis-based (

Polyneoptera The cohort Polyneoptera is a proposed taxonomic ranking for the Orthoptera (grasshoppers, crickets, etc.) and all other Neopteran insects believed to be more closely related to Orthoptera than to any other insect orders. These winged insects, no ...

and

Paraneoptera Paraneoptera or Acercaria is a superorder of insects which includes lice (bark lice and true lice), thrips, and hemipterans, the true bugs. It also includes the extinct order Permopsocida, known from fossils dating from the Early Permian to the ...

) and complete metamorphosis-based groups. It has proved difficult to clarify the relationships between the orders in Polyneoptera because of constant new findings calling for revision of the taxa. For example, the Paraneoptera have turned out to be more closely related to the Endopterygota than to the rest of the Exopterygota. The recent molecular finding that the traditional louse orders

Mallophaga The Mallophaga are a possibly paraphyletic section of lice Louse ( : lice) is the common name for any member of the clade Phthiraptera, which contains nearly 5,000 species of wingless parasitic insects. Phthiraptera has variously been re ...

and

Anoplura Sucking lice (Anoplura, formerly known as Siphunculata) have around 500 species and represent the smaller of the two traditional superfamilies of lice. As opposed to the paraphyletic chewing lice, which are now divided among three suborders, ...

are derived from within

Psocoptera Psocoptera are a paraphyletic group of insects that are commonly known as booklice, barklice or barkflies. The name Psocoptera has been replaced with Psocodea in recent literature, with the inclusion of the former order Phthiraptera into Psoco ...

has led to the new taxon

Psocodea Psocodea is a taxonomic group of insects comprising the bark lice, book lice and parasitic lice. It was formerly considered a superorder, but is now generally considered by entomologists as an order. Despite the greatly differing appearance of ...

. Phasmatodea and Embiidina have been suggested to form the Eukinolabia. Mantodea, Blattodea, and Isoptera are thought to form a monophyletic group termed

Dictyoptera Dictyoptera (from Greek δίκτυον ''diktyon'' "net" and πτερόν ''pteron'' "wing") is an insect superorder that includes two extant orders of polyneopterous insects: the order Blattodea (termites and cockroaches together) and the o ...

. The Exopterygota likely are paraphyletic in regard to the Endopterygota. The Neuropterida are often lumped or split on the whims of the taxonomist. Fleas are now thought to be closely related to boreid mecopterans. Many questions remain in the basal relationships among endopterygote orders, particularly the Hymenoptera.

Evolutionary relationships

Insects are prey for a variety of organisms, including terrestrial vertebrates. The earliest vertebrates on land existed 400 million years ago and were large amphibious

piscivore A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

s. Through gradual evolutionary change,

insectivory A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...

was the next diet type to evolve. Insects were among the earliest terrestrial herbivores and acted as major selection agents on plants. Plants evolved chemical defenses against this herbivory and the insects, in turn, evolved mechanisms to deal with plant toxins. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors. This successful evolutionary pattern has also been used by

mimic MIMIC, known in capitalized form only, is a former simulation computer language developed 1964 by H. E. Petersen, F. J. Sansom and L. M. Warshawsky of Systems Engineering Group within the Air Force Materiel Command at the Wright-Patterson AFB in ...

s. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...

, are beneficial to both organisms. Coevolution has led to the development of very specific

mutualisms Mutualism describes the ecological interaction between two or more species where each species has a net benefit. Mutualism is a common type of ecological interaction. Prominent examples include most vascular plants engaged in mutualistic intera ...

in such systems.

Diversity

Estimates of the total number of insect species, or those within specific orders, often vary considerably. Globally, averages of these estimates suggest there are around 1.5 million beetle species and 5.5 million insect species, with about 1 million insect species currently found and described.

E. O. Wilson Edward Osborne Wilson (June 10, 1929 – December 26, 2021) was an American biologist, naturalist, entomologist and writer. According to David Attenborough, Wilson was the world's leading expert in his specialty of myrmecology, the study of an ...

has estimated that the number of insects living at any one time are around 10 quintillion (10 billion billion). Between 950,000 and 1,000,000 of all described species are insects, so over 50% of all described eukaryotes (1.8 million) are insects (see illustration). With only 950,000 known non-insects, if the actual number of insects is 5.5 million, they may represent over 80% of the total. As only about 20,000 new species of all organisms are described each year, most insect species may remain undescribed, unless the rate of species descriptions greatly increases. Of the 24 orders of insects, four dominate in terms of numbers of described species; at least 670,000 identified species belong to Coleoptera, Diptera, Hymenoptera or Lepidoptera. Percent of insect species

As of 2017, at least 66 insect species extinctions had been recorded in the previous 500 years, generally on oceanic islands. Declines in insect abundance have been attributed to artificial lighting, land use changes such as urbanization or agricultural use, pesticide use, and invasive species. Studies summarized in a 2019 review suggested that a large proportion of insect species is threatened with extinction in the 21st century. The ecologist Manu Sanders notes that the 2019 review was biased by mostly excluding data showing increases or stability in insect population, with the studies limited to specific geographic areas and specific groups of species. A larger 2020 meta-study, analyzing data from 166 long-term surveys, suggested that populations of terrestrial insects are decreasing rapidly, by about 9% per decade. Claims of pending mass insect extinctions or "insect apocalypse" based on a subset of these studies have been popularized in news reports, but often extrapolate beyond the study data or hyperbolize study findings. Other areas have shown increases in some insect species, although trends in most regions are currently unknown. It is difficult to assess long-term trends in insect abundance or diversity because historical measurements are generally not known for many species. Robust data to assess at-risk areas or species is especially lacking for arctic and tropical regions and a majority of the southern hemisphere.

Morphology and physiology

External

Insects have segmented bodies supported by

s, the hard outer covering made mostly of chitin. The segments of the body are organized into three distinctive but interconnected units, or tagmata: a head, a

and an

. The head supports a pair of sensory antennae, a pair of

s, zero to three simple eyes (or

ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...

) and three sets of variously modified appendages that form the mouthparts. The thorax is made up of three segments: the prothorax, mesothorax and the metathorax. Each thoracic segment supports one pair of legs. The meso- and metathoracic segments may each have a pair of

wings A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expre ...

, depending on the insect. The abdomen consists of eleven segments, though in a few species of insects, these segments may be fused together or reduced in size. The abdomen also contains most of the digestive,

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gre ...

excretory Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks aft ...

and reproductive internal structures. Considerable variation and many adaptations in the body parts of insects occur, especially wings, legs, antenna and mouthparts.

Segmentation

The head is enclosed in a hard, heavily sclerotized, unsegmented, exoskeletal head capsule, or epicranium, which contains most of the sensing organs, including the antennae, ocellus or eyes, and the mouthparts. Of all the insect orders, Orthoptera displays the most features found in other insects, including the sutures and

s. Here, the

vertex Vertex, vertices or vertexes may refer to: Science and technology Mathematics and computer science *Vertex (geometry), a point where two or more curves, lines, or edges meet * Vertex (computer graphics), a data structure that describes the positio ...

, or the apex (dorsal region), is situated between the compound eyes for insects with a

hypognathous This glossary of entomology describes terms used in the formal study of insect species by entomologists. A–C A synthetic chlorinated hydrocarbon insecticide, toxic to vertebrates. Though ...

and opisthognathous head. In prognathous insects, the vertex is not found between the compound eyes, but rather, where the

are normally. This is because the primary axis of the head is rotated 90° to become parallel to the primary axis of the body. In some species, this region is modified and assumes a different name. The

is a tagma composed of three sections, the

prothorax The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum ( dorsal), the prosternum ( ventral), and the propleuron ( lateral) o ...

mesothorax The mesothorax is the middle of the three segments of the thorax of hexapods, and bears the second pair of legs. Its principal sclerites (exoskeletal plates) are the mesonotum (dorsal), the mesosternum (ventral), and the mesopleuron (lateral) on ...

and the

metathorax The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites ( exoskeletal plates) are the metanotum (dorsal), the metasternum (ventral), and the metapleuron (lateral) ...

. The anterior segment, closest to the head, is the prothorax, with the major features being the first pair of legs and the pronotum. The middle segment is the mesothorax, with the major features being the second pair of legs and the anterior wings. The third and most posterior segment, abutting the abdomen, is the metathorax, which features the third pair of legs and the posterior wings. Each segment is delineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum (or ''notum'') to distinguish it from the abdominal terga. The two lateral regions are called the pleura (singular: pleuron) and the ventral aspect is called the sternum. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, the mesopleura and metapleura, as well as the mesosternum and metasternum, are used. The

is the largest tagma of the insect, which typically consists of 11–12 segments and is less strongly sclerotized than the head or thorax. Each segment of the abdomen is represented by a sclerotized tergum and sternum. Terga are separated from each other and from the adjacent sterna or pleura by membranes. Spiracles are located in the pleural area. Variation of this ground plan includes the fusion of terga or terga and sterna to form continuous dorsal or ventral shields or a conical tube. Some insects bear a sclerite in the pleural area called a laterotergite. Ventral sclerites are sometimes called laterosternites. During the embryonic stage of many insects and the postembryonic stage of primitive insects, 11 abdominal segments are present. In modern insects there is a tendency toward reduction in the number of the abdominal segments, but the primitive number of 11 is maintained during embryogenesis. Variation in abdominal segment number is considerable. If the Apterygota are considered to be indicative of the ground plan for pterygotes, confusion reigns: adult Protura have 12 segments, Collembola have 6. The orthopteran family Acrididae has 11 segments, and a fossil specimen of Zoraptera has a 10-segmented abdomen.

Exoskeleton

The insect outer skeleton, the cuticle, is made up of two layers: the

epicuticle The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda. Morphology In arthropods, the integument, the external "skin", or ...

, which is a thin and waxy water resistant outer layer and contains no chitin, and a lower layer called the

procuticle The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda. Morphology In arthropods, the integument, the external "skin", or "s ...

. The procuticle is chitinous and much thicker than the epicuticle and has two layers: an outer layer known as the exocuticle and an inner layer known as the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each other in a sandwich pattern, while the exocuticle is rigid and hardened. The exocuticle is greatly reduced in many insects during their

l stages, e.g., caterpillars. It is also reduced in soft-bodied adult insects. Insects are the only

s to have developed active flight capability, and this has played an important role in their success. Their flight muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible. Having their muscles attached to their exoskeletons is efficient and allows more muscle connections.

Internal

Nervous system

The

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

of an insect can be divided into a

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

and a

ventral nerve cord The ventral nerve cord is a major structure of the invertebrate central nervous system. It is the functional equivalent of the vertebrate spinal cord. The ventral nerve cord coordinates neural signaling from the brain to the body and vice versa, i ...

. The head capsule is made up of six fused segments, each with either a pair of ganglia, or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's

esophagus The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...

, called the subesophageal ganglion. The

thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...

segments have one ganglion on each side, which are connected into a pair, one pair per segment. This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction. Some cockroaches have just six ganglia in the abdomen, whereas the wasp ''

Vespa crabro The European hornet (''Vespa crabro'') is the largest eusocial wasp native to Europe. It is also the only true hornet (genus ''Vespa'') found in North America, having been introduced to the United States and Canada from Europe as early as 1840. ...

'' has only two in the thorax and three in the abdomen. Some insects, like the house fly ''

Musca domestica The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic Era, possibly in the Middle East, and has spread all over the world as a commensal of humans. It is the most common f ...

'', have all the body ganglia fused into a single large thoracic ganglion. At least some insects have

nociceptor A nociceptor ("pain receptor" from Latin ''nocere'' 'to harm or hurt') is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sens ...

s, cells that detect and transmit signals responsible for the sensation of pain. This was discovered in 2003 by studying the variation in reactions of larvae of the common fruit-fly

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...

to the touch of a heated probe and an unheated one. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe. Although nociception has been demonstrated in insects, there is no consensus that insects feel pain consciously Insects are capable of learning.

Digestive system

An insect uses its digestive system to extract nutrients and other substances from the food it consumes. Most of this food is ingested in the form of macromolecules and other complex substances like

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s, polysaccharides,

fat In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple est ...

s and nucleic acids. These macromolecules must be broken down by catabolic reactions into smaller molecules like

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

s and

simple sugar Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built. They are usually colorless, water-solub ...

s before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

. There is extensive variation among different orders, life stages, and even castes in the digestive system of insects. This is the result of extreme adaptations to various lifestyles. The present description focuses on a generalized composition of the digestive system of an adult orthopteroid insect, which is considered basal to interpreting particularities of other groups. The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food unidirectionally from the mouth to the anus. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut. The

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary ...

s (element 30 in numbered diagram) in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down. Some insects, like

, have extra-oral digestion. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source. The gut is where almost all of insects' digestion takes place. It can be divided into the foregut,

midgut The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises the portion of the alimentary canal from the end of the foregut a ...

and hindgut.

= Foregut

The first section of the alimentary canal is the foregut (element 27 in numbered diagram), or stomodaeum. The foregut is lined with a cuticular lining made of chitin and

s as protection from tough food. The foregut includes the

buccal cavity The buccal space (also termed the buccinator space) is a fascial space of the head and neck (sometimes also termed fascial tissue spaces or tissue spaces). It is a potential space in the cheek, and is paired on each side. The buccal space is super ...

(mouth),

pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...

and

crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydropon ...

and

proventriculus The proventriculus is part of the digestive system of birds.Encarta World English Dictionary orth American Edition(2007). ''Proventriculus''. Source: (accessed: December 18, 2007) An analogous organ exists in invertebrates and insects. Birds Th ...

(any part may be highly modified), which both store food and signify when to continue passing onward to the midgut. Digestion starts in

(mouth) as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzymes (mostly

amylase An amylase () is an enzyme that catalyses the hydrolysis of starch (Latin ') into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of ...

s), strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders. From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then onward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum, or fluid-filled structure, as in some Diptera species.

= Midgut

= Once food leaves the crop, it passes to the

(element 13 in numbered diagram), also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary. For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut.

= Hindgut

= In the hindgut (element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by

uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown ...

to form fecal pellets. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. Envaginations at the anterior end of the hindgut form the Malpighian tubules, which form the main excretory system of insects.

Excretory system

Insects may have one to hundreds of

Malpighian tubules The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids and tardigrades. The system consists of branching tubules extending from the alimentary canal that absorbs solutes, water ...

(element 20). These tubules remove nitrogenous wastes from the hemolymph of the insect and regulate osmotic balance. Wastes and solutes are emptied directly into the alimentary canal, at the junction between the midgut and hindgut.

Reproductive system

The reproductive system of female insects consist of a pair of

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

, accessory glands, one or more

spermatheca The spermatheca (pronounced plural: spermathecae ), also called receptaculum seminis (plural: receptacula seminis), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, oligochaeta worms and certain other in ...

e, and ducts connecting these parts. The ovaries are made up of a number of egg tubes, called

ovarioles An ovariole is a tubular component of the insect ovary, and the basic unit of egg production. Each ovariole is composed of a germarium (the germline stem cell niche) at the anterior tip, a set of developing oocytes contained within follicles, an ...

, which vary in size and number by species. The number of eggs that the insect is able to make vary by the number of ovarioles with the rate that eggs can develop being also influenced by ovariole design. Female insects are able make eggs, receive and store sperm, manipulate sperm from different males, and lay eggs. Accessory glands or glandular parts of the oviducts produce a variety of substances for sperm maintenance, transport and fertilization, as well as for protection of eggs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called

ootheca An ootheca (pl. ''oothecae'' ) is a type of egg mass made by any member of a variety of species including mollusks (such as ''Turbinella laevigata''), mantises, and cockroaches. The word is a Latinized combination of ''oo-'', meaning "egg", f ...

e. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized. For males, the reproductive system is the

testis A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...

, suspended in the body cavity by tracheae and the

fat body 300px, Stained cells of an insect fat body Fat body is a highly dynamic insect tissue composed primarily of storage cells. It is distributed throughout the insect's internal body cavity; the haemocoel, in close proximity to the epidermis, dig ...

. Most male insects have a pair of testes, inside of which are sperm tubes or follicles that are enclosed within a membranous sac. The follicles connect to the vas deferens by the vas efferens, and the two tubular vasa deferentia connect to a median ejaculatory duct that leads to the outside. A portion of the vas deferens is often enlarged to form the seminal vesicle, which stores the sperm before they are discharged into the female. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. The terminal portion of the ejaculatory duct may be sclerotized to form the intromittent organ, the aedeagus. The remainder of the male reproductive system is derived from embryonic mesoderm, except for the germ cells, or

spermatogonia A spermatogonium (plural: ''spermatogonia'') is an undifferentiated male germ cell. Spermatogonia undergo spermatogenesis to form mature spermatozoa in the seminiferous tubules of the testis. There are three subtypes of spermatogonia in humans: ...

, which descend from the primordial pole cells very early during embryogenesis.

Respiratory system

Structural organization of the heart of the mosquito Anopheles gambiae - image

Insect respiration is accomplished without lungs. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from the ...

(element 8 in numbered diagram). In most insects, air is taken in through openings on the sides of the abdomen and thorax called spiracles. The respiratory system is an important factor that limits the size of insects. As insects get larger, this type of oxygen transport is less efficient and thus the heaviest insect currently weighs less than 100 g. However, with increased atmospheric oxygen levels, as were present in the late

, larger insects were possible, such as dragonflies with wingspans of more than . There are many different patterns of

gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...

demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to

discontinuous gas exchange Discontinuous gas-exchange cycles (DGC), also called discontinuous ventilation or discontinuous ventilatory cycles, follow one of several patterns of arthropod gas exchange that have been documented primarily in insects; they occur when the insect i ...

. During continuous gas exchange,

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

is taken in and

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. Diffusive ventilation is simply a form of continuous gas exchange that occurs by

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...

rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies, which may be held or trapped in special structures.

Circulatory system

Because oxygen is delivered directly to tissues via tracheoles, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system is open; it has no

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenat ...

s or

arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

, and instead consists of little more than a single, perforated dorsal tube that pulses peristaltically. This dorsal blood vessel (element 14) is divided into two sections: the heart and aorta. The dorsal blood vessel circulates the

hemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...

, arthropods' fluid analog of

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

, from the rear of the body cavity forward. Hemolymph is composed of plasma in which

hemocytes A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), a ...

are suspended. Nutrients, hormones, wastes, and other substances are transported throughout the insect body in the hemolymph. Hemocytes include many types of cells that are important for immune responses, wound healing, and other functions. Hemolymph pressure may be increased by muscle contractions or by swallowing air into the digestive system to aid in molting. Hemolymph is also a major part of the open

circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

of other arthropods, such as

spiders Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species di ...

and

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

Reproduction and development

The majority of insects hatch from

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

. The fertilization and development takes place inside the egg, enclosed by a shell (

chorion The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida (in mammals), known as the vitell ...

) that consists of maternal tissue. In contrast to eggs of other arthropods, most insect eggs are drought resistant. This is because inside the chorion two additional membranes develop from embryonic tissue, the amnion and the

serosa The serous membrane (or serosa) is a smooth tissue membrane of mesothelium lining the contents and inner walls of body cavities, which secrete serous fluid to allow lubricated sliding movements between opposing surfaces. The serous membrane ...

. This serosa secretes a cuticle rich in chitin that protects the embryo against desiccation. In Schizophora however the serosa does not develop, but these flies lay their eggs in damp places, such as rotting matter. Some species of insects, like the cockroach '' Blaptica dubia'', as well as juvenile aphids and tsetse flies, are

ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...

. The eggs of ovoviviparous animals develop entirely inside the female, and then hatch immediately upon being laid. Some other species, such as those in the genus of cockroaches known as '' Diploptera'', are

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

, and thus gestate inside the mother and are born alive. Some insects, like parasitic wasps, show polyembryony, where a single fertilized egg divides into many and in some cases thousands of separate embryos. Insects may be ''univoltine'', ''bivoltine'' or ''multivoltine'', i.e. they may have one, two or many broods (generations) in a year. Orgyia recens

Other developmental and reproductive variations include

haplodiploidy Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky. Haplodiploidy determines the sex ...

, polymorphism,

paedomorphosis Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compare ...

peramorphosis In evolutionary developmental biology, heterochrony is any genetically controlled difference in the timing, rate, or duration of a developmental process in an organism compared to its ancestors or other organisms. This leads to changes in the ...

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...

and more rarely

hermaphroditism In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have s ...

. In haplodiploidy, which is a type of sex-determination system, the offspring's sex is determined by the number of sets of

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s an individual receives. This system is typical in bees and wasps. Polymorphism is where a species may have different ''morphs'' or ''forms'', as in the oblong winged katydid, which has four different varieties: green, pink and yellow or tan. Some insects may retain

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...

s that are normally only seen in juveniles; this is called paedomorphosis. In peramorphosis, an opposite sort of phenomenon, insects take on previously unseen traits after they have matured into adults. Many insects display sexual dimorphism, in which males and females have notably different appearances, such as the moth ''

Orgyia recens ''Telochurus recens'', the scarce vapourer, is a moth of the subfamily Lymantriinae found in Europe. The species was first described by Jacob Hübner in 1819. The wingspan is for the males; the females are wingless. The moth flies from June to ...

'' as an exemplar of sexual dimorphism in insects. Some insects use

, a process in which the female can reproduce and give birth without having the eggs

fertilized Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

by a

male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

. Many aphids undergo a form of parthenogenesis, called cyclical parthenogenesis, in which they alternate between one or many generations of asexual and sexual reproduction. In summer, aphids are generally female and parthenogenetic; in the autumn, males may be produced for sexual reproduction. Other insects produced by parthenogenesis are bees, wasps and ants, in which they spawn males. However, overall, most individuals are female, which are produced by fertilization. The males are haploid and the females are diploid. Insect life-histories show adaptations to withstand cold and dry conditions. Some temperate region insects are capable of activity during winter, while some others migrate to a warmer climate or go into a state of

torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...

. Still other insects have evolved mechanisms of

diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press I ...

that allow eggs or pupae to survive these conditions.

Metamorphosis

Metamorphosis in insects is the biological process of development all insects must undergo. There are two forms of metamorphosis: incomplete metamorphosis and complete metamorphosis.

Incomplete metamorphosis

Hemimetabolous Hemimetabolism or hemimetaboly, also called incomplete metamorphosis and paurometabolism,McGavin, George C. ''Essential Entomology: An Order-by-Order Introduction''. Oxford: Oxford University Press, 2001. pp. 20. is the mode of development of certa ...

insects, those with incomplete metamorphosis, change gradually by undergoing a series of molts. An insect molts when it outgrows its exoskeleton, which does not stretch and would otherwise restrict the insect's growth. The molting process begins as the insect's epidermis secretes a new

inside the old one. After this new epicuticle is secreted, the epidermis releases a mixture of enzymes that digests the endocuticle and thus detaches the old cuticle. When this stage is complete, the insect makes its body swell by taking in a large quantity of water or air, which makes the old cuticle split along predefined weaknesses where the old exocuticle was thinnest. Immature insects that go through incomplete metamorphosis are called

nymphs A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are ...

or in the case of dragonflies and damselflies, also

naiads In Greek mythology, the naiads (; grc-gre, ναϊάδες, naïádes) are a type of female spirit, or nymph, presiding over fountains, wells, springs, streams, brooks and other bodies of fresh water. They are distinct from river gods, who ...

. Nymphs are similar in form to the adult except for the presence of wings, which are not developed until adulthood. With each molt, nymphs grow larger and become more similar in appearance to adult insects.

Complete metamorphosis

Holometabolism, or complete metamorphosis, is where the insect changes in four stages, an

or embryo, a

, a

and the adult or

imago In biology, the imago (Latin for "image") is the last stage an insect attains during its metamorphosis, its process of growth and development; it is also called the imaginal stage, the stage in which the insect attains maturity. It follows the f ...

. In these species, an egg hatches to produce a

, which is generally worm-like in form. This worm-like form can be one of several varieties: eruciform (caterpillar-like), scarabaeiform (grub-like), campodeiform (elongated, flattened and active), elateriform (wireworm-like) or vermiform (maggot-like). The larva grows and eventually becomes a

, a stage marked by reduced movement and often sealed within a cocoon. There are three types of pupae: obtect, exarate or coarctate. Obtect pupae are compact, with the legs and other appendages enclosed. Exarate pupae have their legs and other appendages free and extended. Coarctate pupae develop inside the larval skin. Insects undergo considerable change in form during the pupal stage, and emerge as adults. Butterflies are a well-known example of insects that undergo complete metamorphosis, although most insects use this life cycle. Some insects have evolved this system to

hypermetamorphosis Hypermetamorphosis, or heteromorphosis,P.J. Gullan & P.S. Cranston. 2010. The Insects: An Outline of Entomology, 4th Edition. Wiley-Blackwell. is a term used in entomology that refers to a class of variants of holometabolism, that is to say, com ...

. Complete metamorphosis is a trait of the most diverse insect group, the Endopterygota. Endopterygota includes 11 Orders, the largest being Diptera (flies), Lepidoptera (butterflies and moths), and Hymenoptera (bees, wasps, and ants), and Coleoptera (beetles). This form of development is exclusive to insects and not seen in any other arthropods.

Senses and communication

Many insects possess very sensitive and specialized organs of

perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...

. Some insects such as bees can perceive

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

wavelengths, or detect polarized light, while the antennae of male moths can detect the

s of female moths over distances of many kilometers. The yellow paper wasp (''

Polistes versicolor ''Polistes versicolor'', also known as the variegated paper wasp or yellow paper wasp, is a subtropical social wasp within ''Polistes'', the most common genus of paper wasp. It is the most widely distributed of South American wasp species and is ...

'') is known for its wagging movements as a form of communication within the colony; it can waggle with a frequency of 10.6±2.1 Hz (n=190). These wagging movements can signal the arrival of new material into the nest and aggression between workers can be used to stimulate others to increase foraging expeditions. There is a pronounced tendency for there to be a trade-off between visual acuity and chemical or tactile acuity, such that most insects with well-developed eyes have reduced or simple antennae, and vice versa. There are a variety of different mechanisms by which insects perceive sound; while the patterns are not universal, insects can generally hear sound if they can produce it. Different insect species can have varying

hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is audit ...

, though most insects can hear only a narrow range of frequencies related to the frequency of the sounds they can produce. Mosquitoes have been found to hear up to 2 kHz, and some grasshoppers can hear up to 50 kHz. Certain predatory and parasitic insects can detect the characteristic sounds made by their prey or hosts, respectively. For instance, some nocturnal moths can perceive the

ultrasonic Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...

emissions of

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...

s, which helps them avoid predation. Insects that feed on blood have special sensory structures that can detect

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

emissions, and use them to home in on their hosts. Some insects display a rudimentary sense of numbers, such as the solitary wasps that prey upon a single species. The mother wasp lays her eggs in individual cells and provides each egg with a number of live caterpillars on which the young feed when hatched. Some species of wasp always provide five, others twelve, and others as high as twenty-four caterpillars per cell. The number of caterpillars is different among species, but always the same for each sex of larva. The male solitary wasp in the genus ''

Eumenes Eumenes (; grc-gre, Εὐμένης; c. 362316 BC) was a Greek general and satrap. He participated in the Wars of Alexander the Great, serving as both Alexander's personal secretary and as a battlefield commander. He later was a participant in t ...

'' is smaller than the female, so the mother of one species supplies him with only five caterpillars; the larger female receives ten caterpillars in her cell.

Light production and vision

A few insects, such as members of the families Poduridae and Onychiuridae (Collembola),

Mycetophilidae The Mycetophilidae are a family of small flies, forming the bulk of those species known as fungus gnats. About 3000 described species are placed in 150 genera, but the true number of species is undoubtedly much higher. They are generally found i ...

(Diptera) and the beetle families

Lampyridae The Lampyridae are a family of elateroid beetles with more than 2,000 described species, many of which are light-emitting. They are soft-bodied beetles commonly called fireflies, lightning bugs, or glowworms for their conspicuous production ...

Phengodidae The beetle family Phengodidae is known also as glowworm beetles, whose larvae are known as glowworms. The females and larvae have bioluminescent organs. They occur throughout the New World from extreme southern Canada to Chile. The recently re ...

Elateridae Elateridae or click beetles (or "typical click beetles" to distinguish them from the related families Cerophytidae and Eucnemidae, which are also capable of clicking) are a family of beetles. Other names include elaters, snapping beetles, sp ...

and Staphylinidae are bioluminescent. The most familiar group are the

fireflies The Lampyridae are a family of elateroid beetles with more than 2,000 described species, many of which are light-emitting. They are soft-bodied beetles commonly called fireflies, lightning bugs, or glowworms for their conspicuous production ...

, beetles of the family Lampyridae. Some species are able to control this light generation to produce flashes. The function varies with some species using them to attract mates, while others use them to lure prey. Cave dwelling larvae of ''

Arachnocampa ''Arachnocampa'' is a genus of nine fungus gnat species which have a bioluminescent larval stage, akin to the larval stage of glowworm beetles. The species of ''Arachnocampa'' are endemic to Australia and New Zealand, dwelling in caves and grot ...

'' (Mycetophilidae, fungus gnats) glow to lure small flying insects into sticky strands of silk. Some fireflies of the genus '' Photuris''

the flashing of female ''

Photinus Photinus (Greek Φωτεινός; died 376), was a Christian bishop of Sirmium in Pannonia Secunda (today the town Sremska Mitrovica in Serbia), best known for denying the incarnation of Christ, thus being considered a heresiarch by the Catholic C ...

'' species to attract males of that species, which are then captured and devoured. The colors of emitted light vary from dull blue (''Orfelia fultoni'', Mycetophilidae) to the familiar greens and the rare reds (''Phrixothrix tiemanni'', Phengodidae). Most insects, except some species of

cave crickets The orthopteran family Rhaphidophoridae of the suborder Ensifera has a worldwide distribution. Common names for these insects include cave wētā, cave crickets, camelback crickets, camel crickets, Hogan bugs, spider crickets (sometimes shorte ...

, are able to perceive light and dark. Many species have acute vision capable of detecting minute movements. The eyes may include simple eyes or

as well as

s of varying sizes. Many species are able to detect light in the

and

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

wavelengths. Color vision has been demonstrated in many species and phylogenetic analysis suggests that UV-green-blue

trichromacy Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal exp ...

existed from at least the Devonian period between 416 and 359 million years ago. The individual lenses in compound eyes are immobile, and it was therefore presumed that insects were not able to focus. But research on fruit flies, which is the only insects studied so far, has shown that photoreceptor cells underneath each lens move rapidly in and out of focus in a series of movements called photoreceptor microsaccades. This gives them a much clearer image of the world than previously assumed.

Sound production and hearing

Insects were the earliest organisms to produce and sense sounds. Hearing has evolved independently at least 19 times in different insect groups. Insects make sounds mostly by mechanical action of appendages. In grasshoppers and crickets, this is achieved by

stridulation Stridulation is the act of producing sound by rubbing together certain body parts. This behavior is mostly associated with insects, but other animals are known to do this as well, such as a number of species of fish, snakes and spiders. The mech ...

Cicada The cicadas () are a superfamily, the Cicadoidea, of insects in the order Hemiptera (true bugs). They are in the suborder Auchenorrhyncha, along with smaller jumping bugs such as leafhoppers and froghoppers. The superfamily is divided into tw ...

s make the loudest sounds among the insects by producing and amplifying sounds with special modifications to their body to form

tymbal The tymbal (or timbal) is the corrugated exoskeletal structure used to produce sounds in insects. In male cicadas, the tymbals are membranes in the abdomen, responsible for the characteristic sound produced by the insect. In tiger moths, the t ...

s and associated musculature. The African

cicada The cicadas () are a superfamily, the Cicadoidea, of insects in the order Hemiptera (true bugs). They are in the suborder Auchenorrhyncha, along with smaller jumping bugs such as leafhoppers and froghoppers. The superfamily is divided into tw ...

'' Brevisana brevis'' has been measured at 106.7 decibels at a distance of . Some insects, such as the ''

Helicoverpa zea ''Helicoverpa zea, ''commonly known as the corn earworm, is a species (formerly in the genus ''Heliothis'') in the family Noctuidae. The larva of the moth ''Helicoverpa zea'' is a major agricultural pest. Since it is polyphagous (feeds on many ...

'' moths,

hawk moth The Sphingidae are a family of moths (Lepidoptera) called sphinx moths, also colloquially known as hawk moths, with many of their caterpillars known as “hornworms”; it includes about 1,450 species. It is best represented in the tropics, but ...

s and Hedylid butterflies, can hear

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...

and take evasive action when they sense that they have been detected by bats. Some moths produce ultrasonic clicks that were once thought to have a role in jamming bat echolocation. The ultrasonic clicks were subsequently found to be produced mostly by unpalatable moths to warn bats, just as warning colorations are used against predators that hunt by sight. Some otherwise palatable moths have evolved to

these calls. More recently, the claim that some moths can jam bat sonar has been revisited. Ultrasonic recording and high-speed infrared videography of bat-moth interactions suggest the palatable tiger moth really does defend against attacking big brown bats using ultrasonic clicks that jam bat sonar. Very low sounds are also produced in various species of Coleoptera, Hymenoptera, Lepidoptera,

Mantodea Mantises are an order (Mantodea) of insects that contains over 2,400 species in about 460 genera in 33 families. The largest family is the Mantidae ("mantids"). Mantises are distributed worldwide in temperate and tropical habitats. They ha ...

and Neuroptera. These low sounds are simply the sounds made by the insect's movement. Through microscopic stridulatory structures located on the insect's muscles and joints, the normal sounds of the insect moving are amplified and can be used to warn or communicate with other insects. Most sound-making insects also have

tympanal organ A tympanal organ (or tympanic organ) is a hearing organ in insects, consisting of a membrane ( tympanum) stretched across a frame backed by an air sac and associated sensory neurons. Sounds vibrate the membrane, and the vibrations are sensed by ...

s that can perceive airborne sounds. Some species in Hemiptera, such as the corixids (water boatmen), are known to communicate via underwater sounds. Most insects are also able to sense

vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, su ...

s transmitted through surfaces. Cricket in garage with familiar call. Communication using surface-borne vibrational signals is more widespread among insects because of size constraints in producing air-borne sounds. Insects cannot effectively produce low-frequency sounds, and high-frequency sounds tend to disperse more in a dense environment (such as

foliage A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, s ...

), so insects living in such environments communicate primarily using substrate-borne vibrations. The mechanisms of production of vibrational signals are just as diverse as those for producing sound in insects. Some species use vibrations for communicating within members of the same species, such as to attract mates as in the songs of the

shield bug The Pentatomoidea are a superfamily of insects in the Heteroptera suborder of the Hemiptera order. As Hemiptera, they share a common arrangement of sucking mouthparts. The roughly 7000 species under Pentatomoidea are divided into 21 families (16 ...

Nezara viridula ''Nezara viridula'', commonly known as the southern green stink bug (USA), southern green shield bug (UK) or green vegetable bug (Australia and New Zealand), is a plant-feeding stink bug. Believed to have originated in Ethiopia, it can now be fo ...

''. Vibrations can also be used to communicate between entirely different species; lycaenid (gossamer-winged butterfly) caterpillars, which are

myrmecophilous Myrmecophily ( , ) is the term applied to positive interspecies associations between ants and a variety of other organisms, such as plants, other arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its ...

(living in a mutualistic association with ants) communicate with ants in this way. The

Madagascar hissing cockroach The Madagascar hissing cockroach (''Gromphadorhina portentosa''), also known as the hissing cockroach or simply hisser, is one of the largest species of cockroach, reaching at maturity. They are native to the island of Madagascar, which is off ...

has the ability to press air through its spiracles to make a hissing noise as a sign of aggression; the

death's-head hawkmoth The name death's-head hawkmoth refers to any of three moth species of the genus ''Acherontia'' (''Acherontia atropos'', ''Acherontia styx'' and ''Acherontia lachesis''). The former species is found in Europe and throughout Africa, the latter t ...

makes a squeaking noise by forcing air out of their pharynx when agitated, which may also reduce aggressive worker honey bee behavior when the two are close.

Chemical communication

Chemical communications in animals rely on a variety of aspects including taste and smell. Chemoreception is the physiological response of a sense organ (i.e. taste or smell) to a chemical stimulus where the chemicals act as signals to regulate the state or activity of a cell. A semiochemical is a message-carrying chemical that is meant to attract, repel, and convey information. Types of semiochemicals include pheromones and kairomones. One example is the butterfly '' Phengaris arion ''which uses chemical signals as a form of mimicry to aid in predation. In addition to the use of sound for communication, a wide range of insects have evolved chemical means for communication. These

semiochemical A semiochemical, from the Greek wiktionary:σημεῖον, σημεῖον (''semeion''), meaning "signal", is a chemical substance or mixture released by an organism that affects the behaviors of other individuals. Semiochemical communication c ...

s are often derived from plant metabolites including those meant to attract, repel and provide other kinds of information.

Pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s, a type of semiochemical, are used for attracting mates of the opposite sex, for aggregating

conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...

individuals of both sexes, for deterring other individuals from approaching, to mark a trail, and to trigger aggression in nearby individuals.

Allomone An allomone (from Ancient Greek ' "other" and pheromone) is a type of semiochemical produced and released by an individual of one species that affects the behaviour of a member of another species to the benefit of the originator but not the rec ...

s benefit their producer by the effect they have upon the receiver.

Kairomone A kairomone (a coinage using the Greek καιρός ''opportune moment'', paralleling pheromone"kairomone, n.". OED Online. September 2012. Oxford University Press. http://www.oed.com/view/Entry/241005?redirectedFrom=kairomone (accessed 3 Octo ...

s benefit their receiver instead of their producer. Synomones benefit the producer and the receiver. While some chemicals are targeted at individuals of the same species, others are used for communication across species. The use of scents is especially well-developed in social insects. are nonstructural materials produced and secreted to the cuticle surface to fight desiccation and

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

s. They are important, too, as pheromones, especially in social insects.

Social behavior

Social insect Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...

s, such as

s and many bees and

s, are the most familiar species of

eusocial Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping gen ...

animals. They live together in large well-organized colonies that may be so tightly integrated and genetically similar that the colonies of some species are sometimes considered

superorganism A superorganism or supraorganism is a group of synergetically interacting organisms of the same species. A community of synergetically interacting organisms of different species is called a holobiont. Concept The term superorganism is used m ...

s. It is sometimes argued that the various species of

honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosm ...

are the only invertebrates (and indeed one of the few non-human groups) to have evolved a system of abstract symbolic communication where a behavior is used to represent and convey specific information about something in the environment. In this communication system, called dance language, the angle at which a bee dances represents a direction relative to the sun, and the length of the dance represents the distance to be flown. Though perhaps not as advanced as honey bees,

bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related genera ...

s also potentially have some social communication behaviors. ''

Bombus terrestris ''Bombus terrestris'', the buff-tailed bumblebee or large earth bumblebee, is one of the most numerous bumblebee species in Europe. It is one of the main species used in greenhouse pollination, and so can be found in many countries and areas wher ...

'', for example, exhibit a faster learning curve for visiting unfamiliar, yet rewarding flowers, when they can see a conspecific foraging on the same species. Only insects that live in nests or colonies demonstrate any true capacity for fine-scale spatial orientation or homing. This can allow an insect to return unerringly to a single hole a few millimeters in diameter among thousands of apparently identical holes clustered together, after a trip of up to several kilometers' distance. In a phenomenon known as

philopatry Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derive ...

, insects that hibernate have shown the ability to recall a specific location up to a year after last viewing the area of interest. A few insects seasonally migrate large distances between different geographic regions (e.g., the overwintering areas of the monarch butterfly).

Care of young

The

insects build nests, guard eggs, and provide food for offspring full-time. Most insects, however, lead short lives as adults, and rarely interact with one another except to mate or compete for mates. A small number exhibit some form of

parental care Parental care is a behavioural and evolutionary strategy adopted by some animals, involving a parental investment being made to the evolutionary fitness of offspring. Patterns of parental care are widespread and highly diverse across the animal ki ...

, where they will at least guard their eggs, and sometimes continue guarding their offspring until adulthood, and possibly even feeding them. Another simple form of parental care is to construct a nest (a burrow or an actual construction, either of which may be simple or complex), store provisions in it, and lay an egg upon those provisions. The adult does not contact the growing offspring, but it nonetheless does provide food. This sort of care is typical for most species of bees and various types of wasps.

Locomotion

Flight

Insects are the only group of

s to have developed flight. The evolution of insect wings has been a subject of debate. Some

entomologists Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...

suggest that the wings are from paranotal lobes, or extensions from the insect's exoskeleton called the

nota Nota Sports and Racing Cars is an automobile manufacturer in Australia. The company was founded by Guy Buckingham in 1952. He was an aircraft engineer and used his expertise to build triangulated spaceframed sportscars. Possibly Australia's ...

, called the ''paranotal theory''. Other theories are based on a pleural origin. These theories include suggestions that wings originated from modified gills, spiracular flaps or as from an appendage of the epicoxa. The ''epicoxal theory'' suggests the insect wings are modified epicoxal exites, a modified appendage at the base of the legs or coxa. In the Carboniferous age, some of the ''

Meganeura ''Meganeura'' is a genus of extinct insects from the Late Carboniferous (approximately 300 million years ago). They resembled and are related to the present-day dragonflies and damselflies, and were predatory, with their diet mainly consisting o ...

'' dragonflies had as much as a wide wingspan. The appearance of gigantic insects has been found to be consistent with high atmospheric oxygen. The respiratory system of insects constrains their size, however the high oxygen in the atmosphere allowed larger sizes. The largest flying insects today are much smaller, with the largest wingspan belonging to the white witch moth ('' Thysania agrippina''), at approximately . Insect flight has been a topic of great interest in

aerodynamics Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dy ...

due partly to the inability of steady-state theories to explain the lift generated by the tiny wings of insects. But insect wings are in motion, with flapping and vibrations, resulting in churning and

eddies In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid b ...

, and the misconception that physics says "bumblebees can't fly" persisted throughout most of the twentieth century. Unlike

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, many small insects are swept along by the

prevailing winds In meteorology, prevailing wind in a region of the Earth's surface is a surface wind that blows predominantly from a particular direction. The dominant winds are the trends in direction of wind with the highest speed over a particular point on ...

although many of the larger insects are known to make migrations.

Aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s are known to be transported long distances by low-level jet streams. As such, fine line patterns associated with converging winds within

weather radar Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse- ...

imagery, like the WSR-88D radar network, often represent large groups of insects. Radar can also be deliberately used to monitor insects.

Walking

Many adult insects use six legs for walking, with an alternating tripod gait. This allows for rapid walking while always having a stable stance; it has been studied extensively in

cockroach Cockroaches (or roaches) are a Paraphyly, paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are we ...

es and

s. For the first step, the middle right leg and the front and rear left legs are in contact with the ground and move the insect forward, while the front and rear right leg and the middle left leg are lifted and moved forward to a new position. When they touch the ground to form a new stable triangle the other legs can be lifted and brought forward in turn and so on. The purest form of the tripedal gait is seen in insects moving at high speeds. However, this type of locomotion is not rigid and insects can adapt a variety of gaits. For example, when moving slowly, turning, avoiding obstacles, climbing or slippery surfaces, four (tetrapod) or more feet (wave-gait) may be touching the ground. Insects can also adapt their gait to cope with the loss of one or more limbs. Cockroaches are among the fastest insect runners and, at full speed, adopt a bipedal run to reach a high velocity in proportion to their body size. As cockroaches move very quickly, they need to be video recorded at several hundred frames per second to reveal their gait. More sedate locomotion is seen in the stick insects or walking sticks ( Phasmatodea). A few insects have evolved to walk on the surface of the water, especially members of the

Gerridae The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, or water skimmers. Consistent with the classification of the Gerridae as tr ...

family, commonly known as water striders. A few species of ocean-skaters in the genus '' Halobates'' even live on the surface of open oceans, a habitat that has few insect species. Insect walking is of particular interest as practical form of

robot locomotion Robot locomotion is the collective name for the various methods that robots use to transport themselves from place to place. Wheeled robots are typically quite energy efficient and simple to control. However, other forms of locomotion may be more ...

. The study of insects and

biped Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

s has a significant impact on possible robotic methods of transport. This may allow new hexapod robots to be designed that can traverse

terrain Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin wo ...

that robots with wheels may be unable to handle.

Swimming

A large number of insects live either part or the whole of their lives underwater. In many of the more primitive orders of insect, the immature stages are spent in an aquatic environment. Some groups of insects, like certain

water beetle A water beetle is a generalized name for any beetle that is adapted to living in water at any point in its life cycle. Most water beetles can only live in fresh water, with a few marine species that live in the intertidal zone or littoral zone. Th ...

s, have aquatic adults as well. Many of these species have adaptations to help in under-water locomotion. Water beetles and water bugs have legs adapted into paddle-like structures. Dragonfly

use jet propulsion, forcibly expelling water out of their rectal chamber. Some species like the

water strider The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, or water skimmers. Consistent with the classification of the Gerridae as tr ...

s are capable of walking on the surface of water. They can do this because their claws are not at the tips of the legs as in most insects, but recessed in a special groove further up the leg; this prevents the claws from piercing the water's surface film. Other insects such as the

Rove beetle The rove beetles are a family (Staphylinidae) of beetles, primarily distinguished by their short elytra (wing covers) that typically leave more than half of their abdominal segments exposed. With roughly 63,000 species in thousands of genera, the ...

Stenus ''Stenus'' is a genus of semiaquatic rove beetles in the subfamily Steninae, and one of the largest genus in the kingdom Animalia, with some 2700 known species worldwide (only the beetle genus ''Agrilus'' is comparable in size). They are preda ...

'' are known to emit pygidial gland secretions that reduce surface tension making it possible for them to move on the surface of water by Marangoni propulsion (also known by the

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

term ''Entspannungsschwimmen'').

Ecology

Insect ecology is the scientific study of how insects, individually or as a community, interact with the surrounding environment or

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

. Insects play one of the most important roles in their ecosystems, which includes many roles, such as soil turning and aeration, dung burial, pest control, pollination and wildlife nutrition. An example is the

s, which are scavengers that feed on dead animals and fallen trees and thereby

recycle Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

biological materials into forms found useful by other

s. These insects, and others, are responsible for much of the process by which

topsoil Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Description Topsoil is composed of mineral particles and organic matt ...

is created.

Defense and predation

Insects are mostly soft bodied, fragile and almost defenseless compared to other, larger lifeforms. The immature stages are small, move slowly or are immobile, and so all stages are exposed to

predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

and parasitism. Insects then have a variety of defense strategies to avoid being attacked by predators or parasitoids. These include

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

, mimicry, toxicity and active defense.

Camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

is an important defense strategy, which involves the use of coloration or shape to blend into the surrounding environment. This sort of protective coloration is common and widespread among beetle families, especially those that feed on wood or vegetation, such as many of the

leaf beetle The insects of the beetle family Chrysomelidae are commonly known as leaf beetles, and include over 37,000 (and probably at least 50,000) species in more than 2,500 genera, making up one of the largest and most commonly encountered of all beetle ...

s (family Chrysomelidae) or

weevil Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and herbivorous. Approximately 97,000 species of weevils are known. They belong to several families, ...

s. In some of these species, sculpturing or various colored scales or hairs cause the beetle to resemble bird dung or other inedible objects. Many of those that live in sandy environments blend in with the coloration of the substrate. Most phasmids are known for effectively replicating the forms of sticks and leaves, and the bodies of some species (such as ''O. macklotti'' and ''Palophus centaurus'') are covered in mossy or lichenous outgrowths that supplement their disguise. Very rarely, a species may have the ability to change color as their surroundings shift (''Bostra scabrinota''). In a further behavioral adaptation to supplement crypsis, a number of species have been noted to perform a rocking motion where the body is swayed from side to side that is thought to reflect the movement of leaves or twigs swaying in the breeze. Another method by which stick insects avoid predation and resemble twigs is by feigning death (

catalepsy Catalepsy (from Ancient Greek , , "seizing, grasping") is a nervous condition characterized by muscular rigidity and fixity of posture regardless of external stimuli, as well as decreased sensitivity to pain. Signs and symptoms Symptoms in ...

), where the insect enters a motionless state that can be maintained for a long period. The nocturnal feeding habits of adults also aids Phasmatodea in remaining concealed from predators. Another defense that often uses color or shape to deceive potential enemies is mimicry. A number of

longhorn beetle The longhorn beetles (Cerambycidae), also known as long-horned or longicorns, are a large family of beetles, with over 35,000 species described. Most species are characterized by extremely long antennae, which are often as long as or longer than ...

s (family Cerambycidae) bear a striking resemblance to

s, which helps them avoid predation even though the beetles are in fact harmless. Batesian and Müllerian mimicry complexes are commonly found in Lepidoptera. Genetic polymorphism and natural selection give rise to otherwise edible species (the mimic) gaining a survival advantage by resembling inedible species (the model). Such a mimicry complex is referred to as ''Batesian''. One of the most famous examples, where the

viceroy butterfly The viceroy (''Limenitis archippus'') is a North American butterfly. It was long thought to be a Batesian mimic of the monarch butterfly, but since the viceroy is also distasteful to predators, it is now considered a Müllerian mimic instead. T ...

was long believed to be a Batesian mimic of the inedible

monarch A monarch is a head of stateWebster's II New College DictionarMonarch Houghton Mifflin. Boston. 2001. p. 707. for life or until abdication, and therefore the head of state of a monarchy. A monarch may exercise the highest authority and power i ...

, was later disproven, as the viceroy is more toxic than the monarch, and this resemblance is now considered to be a case of Müllerian mimicry. In Müllerian mimicry, inedible species, usually within a taxonomic order, find it advantageous to resemble each other so as to reduce the sampling rate by predators who need to learn about the insects' inedibility. Taxa from the toxic genus ''

Heliconius ''Heliconius'' comprises a colorful and widespread genus of brush-footed butterflies commonly known as the longwings or heliconians. This genus is distributed throughout the tropical and subtropical regions of the New World, from South America ...

'' form one of the most well known Müllerian complexes. Chemical defense is another important defense found among species of Coleoptera and Lepidoptera, usually being advertised by bright colors, such as the monarch butterfly. They obtain their toxicity by sequestering the chemicals from the plants they eat into their own tissues. Some Lepidoptera manufacture their own toxins. Predators that eat poisonous butterflies and moths may become sick and vomit violently, learning not to eat those types of species; this is actually the basis of Müllerian mimicry. A predator who has previously eaten a poisonous lepidopteran may avoid other species with similar markings in the future, thus saving many other species as well. Some

ground beetle Ground beetles are a large, cosmopolitan family of beetles, the Carabidae, with more than 40,000 species worldwide, around 2,000 of which are found in North America and 2,700 in Europe. As of 2015, it is one of the 10 most species-rich animal f ...

s of the family Carabidae can spray chemicals from their abdomen with great accuracy, to repel predators.

Pollination

Pollination is the process by which pollen is transferred in the reproduction of plants, thereby enabling fertilisation and

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...

. Most flowering plants require an animal to do the transportation. While other animals are included as pollinators, the majority of pollination is done by insects. Because insects usually receive benefit for the pollination in the form of energy rich nectar it is a grand example of mutualism. The various flower traits (and combinations thereof) that differentially attract one type of pollinator or another are known as

pollination syndrome Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic (wind and water) or biotic, such as birds, bees, flies, and so forth through a process c ...

s. These arose through complex plant-animal adaptations. Pollinators find flowers through bright colorations, including ultraviolet, and attractant

pheromones A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

. The study of pollination by insects is known as '' anthecology''.

Parasitism

Many insects are parasites of other insects such as the parasitoid wasps. These insects are known as entomophagous parasites. They can be beneficial due to their devastation of pests that can destroy crops and other resources. Many insects have a parasitic relationship with humans such as the mosquito. These insects are known to spread diseases such as

malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...

and

yellow fever Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains – particularly in the back – and headaches. Symptoms typically improve within five days. ...

and because of such, mosquitoes indirectly cause more deaths of humans than any other animal.

Relationship to humans

As pests

Many insects are considered pests by humans. Insects commonly regarded as pests include those that are parasitic (''e.g.'' lice, bed bugs), transmit diseases (

mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...

es,

), damage structures (

s), or destroy agricultural goods (

locust Locusts (derived from the Vulgar Latin ''locusta'', meaning grasshopper) are various species of short-horned grasshoppers in the family Acrididae that have a swarming phase. These insects are usually solitary, but under certain circumstanc ...

s). Many entomologists are involved in various forms of pest control, as in research for companies to produce insecticides, but increasingly rely on methods of biological pest control, or biocontrol. Biocontrol uses one organism to reduce the population density of another organism—the pest—and is considered a key element of

integrated pest management Integrated pest management (IPM), also known as integrated pest control (IPC) is a broad-based approach that integrates both chemical and non-chemical practices for economic control of pests. IPM aims to suppress pest populations below the econ ...

. Despite the large amount of effort focused at controlling insects, human attempts to kill pests with insecticides can backfire. If used carelessly, the poison can kill all kinds of organisms in the area, including insects' natural predators, such as birds, mice and other insectivores. The effects of

DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

's use exemplifies how some insecticides can threaten wildlife beyond intended populations of pest insects.

In beneficial roles

Although pest insects attract the most attention, many insects are beneficial to the environment and to

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...

s. Some insects, like

s, bees, butterflies and

pollinate Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...

s. Pollination is a mutualistic relationship between plants and insects. As insects gather nectar from different plants of the same species, they also spread pollen from plants on which they have previously fed. This greatly increases plants' ability to cross-pollinate, which maintains and possibly even improves their evolutionary fitness. This ultimately affects humans since ensuring healthy crops is critical to

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...

. As well as pollination ants help with seed distribution of plants. This helps to spread the plants, which increases plant diversity. This leads to an overall better environment. A serious environmental problem is the decline of populations of pollinator insects, and a number of species of insects are now cultured primarily for

pollination management Pollination management is the horticultural practices that accomplish or enhance pollination of a crop, to improve yield or quality, by understanding of the particular crop's pollination needs, and by knowledgeable management of pollenizers, p ...

in order to have sufficient pollinators in the field,

orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of ...

or greenhouse at bloom time. Another solution, as shown in Delaware, has been to raise native plants to help support native pollinators like '' L. vierecki''. The economic value of pollination by insects has been estimated to be about $34 billion in the US alone. Products made by insects. Insects also produce useful substances such as

wax Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...

, lacquer and

Honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosm ...

s have been cultured by humans for thousands of years for honey, although contracting for crop pollination is becoming more significant for

beekeeper A beekeeper is a person who keeps honey bees. Beekeepers are also called honey farmers, apiarists, or less commonly, apiculturists (both from the Latin '' apis'', bee; cf. apiary). The term beekeeper refers to a person who keeps honey bees i ...

s. The silkworm has greatly affected human history, as silk-driven trade established relationships between China and the rest of the world. Pest control. Insectivorous insects, or insects that feed on other insects, are beneficial to humans if they eat insects that could cause damage to agriculture and human structures. For example,

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s feed on crops and cause problems for farmers, but

ladybug Coccinellidae () is a widespread family of small beetles ranging in size from . They are commonly known as ladybugs in North America and ladybirds in Great Britain. Some entomologists prefer the names ladybird beetles or lady beetles as they ...

s feed on aphids, and can be used as a means to significantly reduce pest aphid populations. While

s are perhaps more visible predators of insects, insects themselves account for the vast majority of insect consumption. Ants also help control animal populations by consuming small vertebrates. Without predators to keep them in check, insects can undergo almost unstoppable

population explosion Overpopulation or overabundance is a phenomenon in which a species' population becomes larger than the carrying capacity of its environment. This may be caused by increased birth rates, lowered mortality rates, reduced predation or large scale m ...

s. Medical uses. Insects are also used in medicine, for example fly larvae (

maggot A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies. ...

s) were formerly used to treat wounds to prevent or stop gangrene, as they would only consume dead flesh. This treatment is finding modern usage in some hospitals. Recently insects have also gained attention as potential sources of drugs and other medicinal substances. Adult insects, such as crickets and insect larvae of various kinds, are also commonly used as fishing bait.

In research

Insects play important roles in biological research. For example, because of its small size, short generation time and high

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

, the common fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

'' is a model organism for studies in the

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...

of eukaryotes. ''D. melanogaster'' has been an essential part of studies into principles like genetic linkage, interactions between genes,

chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

genetics,

development Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material is reshaped * Photograph ...

, behavior and

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

. Because genetic systems are well conserved among eukaryotes, understanding basic cellular processes like

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

in fruit flies can help to understand those processes in other eukaryotes, including humans. The

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

of ''D. melanogaster'' was

sequenced In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which suc ...

in 2000, reflecting the organism's important role in biological research. It was found that 70% of the fly genome is similar to the human genome, supporting the evolution theory.

As food

In some cultures, insects form part of the normal diet. In Africa, for instance, locally abundant species of both

s and

s are a common traditional human food source. Some, especially

deep-fried Deep frying (also referred to as deep fat frying) is a cooking method in which food is submerged in hot fat, traditionally lard but today most commonly oil, as opposed to the shallow oil used in conventional frying done in a frying pan. Norma ...

s, are considered to be delicacies. Insects have a high protein content for their mass, and some authors suggest their potential as a major source of

in human

nutrition Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient ...

. In most first-world countries, however,

entomophagy Entomophagy (, from Greek ἔντομον ', 'insect', and φαγεῖν ', 'to eat') is the practice of eating insects. An alternative term is insectivory. Terms for organisms that practice entomophagy are ''entomophage'' and ''insectivore' ...

(the eating of insects), is

taboo A taboo or tabu is a social group's ban, prohibition, or avoidance of something (usually an utterance or behavior) based on the group's sense that it is excessively repulsive, sacred, or allowed only for certain persons.''Encyclopædia Britannica ...

. They are also recommended by

militaries A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...

as a

survival Survival, or the act of surviving, is the propensity of something to continue existing, particularly when this is done despite conditions that might kill or destroy it. The concept can be applied to humans and other living things (or, hypotheti ...

food for troops in adversity. Since it is impossible to eliminate pest insects from the human food chain, insects are inadvertently present in many foods, especially grains. Food safety laws in many countries do not prohibit insect parts in food, but rather limit their quantity. According to cultural materialist anthropologist

Marvin Harris Marvin Harris (August 18, 1927 – October 25, 2001) was an American anthropologist. He was born in Brooklyn, New York City. A prolific writer, he was highly influential in the development of cultural materialism and environmental determinism. ...

, the eating of insects is taboo in cultures that have other protein sources such as fish or livestock. Because of the abundance of insects and a worldwide concern of food shortages, the

Food and Agriculture Organization The Food and Agriculture Organization of the United Nations (FAO)french: link=no, Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is an intern ...

of the

United Nations The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmoniz ...

considers that the world may have to, in the future, regard the prospects of eating insects as a food staple. Insects are noted for their nutrients, having a high content of protein, minerals and fats and are eaten by one-third of the global population.

As feed

Several insect species such as the

black soldier fly ''Hermetia illucens'', the black soldier fly, is a common and widespread fly of the family Stratiomyidae. Distribution This species is native to the Neotropical realm, but in recent decades has spread across all continents, becoming virtually ...

or the housefly in their

forms, as well as beetle larvae such as mealworms can be processed and used as feed for farmed animals such as chicken, fish and pigs.

In other products

Black soldier fly ''Hermetia illucens'', the black soldier fly, is a common and widespread fly of the family Stratiomyidae. Distribution This species is native to the Neotropical realm, but in recent decades has spread across all continents, becoming virtually ...

larvae can provide

, fats for use in

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protect ...

, and chitin. Also, insect cooking oil, insect butter and fatty alcohols can be made from such insects as the superworm (''

Zophobas morio ''Zophobas morio'' is a species of darkling beetle, whose larvae are known by the common name superworm, kingworm, morio worm or simply Zophobas. Superworms are common in the reptile pet industry as food, along with giant mealworms, which are '' ...

'').

As pets

Many species of insects are sold and kept as

pet A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...

s. There are special hobbyist magazines such as "Bugs" (now discontinued).

In culture

Scarab beetles The family Scarabaeidae, as currently defined, consists of over 30,000 species of beetles worldwide; they are often called scarabs or scarab beetles. The classification of this family has undergone significant change in recent years. Several sub ...

held religious and cultural symbolism in Old Egypt,

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders ...

and some shamanistic Old World cultures. The ancient

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

regarded

s as symbols of rebirth or immortality. In

Mesopotamia Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the ...

n literature, the epic poem of

Gilgamesh sux, , label=none , image = Hero lion Dur-Sharrukin Louvre AO19862.jpg , alt = , caption = Possible representation of Gilgamesh as Master of Animals, grasping a lion in his left arm and snake in his right hand, in an Assy ...

has allusions to

Odonata Odonata is an order of flying insects that includes the dragonflies and damselflies. Members of the group first appeared during the Triassic, though members of their total group, Odonatoptera, first appeared in Late Carboniferous. The two com ...

that signify the impossibility of immortality. Among the Aborigines of Australia of the

Arrernte Arrernte (also spelt Aranda, etc.) is a descriptor related to a group of Aboriginal Australian peoples from Central Australia. It may refer to: * Arrernte (area), land controlled by the Arrernte Council (?) * Arrernte people, Aboriginal Australi ...

language groups, honey ants and

witchetty grub The witchetty grub (also spelled witchety grub or witjuti grub) is a term used in Australia for the large, white, wood-eating larvae of several moths. In particular, it applies to the larvae of the cossid moth ''Endoxyla leucomochla'', which fee ...

s served as personal clan totems. In the case of the 'San' bush-men of the

Kalahari The Kalahari Desert is a large semi-arid sandy savanna in Southern Africa extending for , covering much of Botswana, and parts of Namibia and South Africa. It is not to be confused with the Angolan, Namibian, and South African Namib coasta ...

, it is the

praying mantis Mantises are an order (Mantodea) of insects that contains over 2,400 species in about 460 genera in 33 families. The largest family is the Mantidae ("mantids"). Mantises are distributed worldwide in temperate and tropical habitats. They ha ...

that holds much cultural significance including creation and zen-like patience in waiting.

Notes

References

External links

Insect species and observations on iNaturalist

Insects of North America

Overview of Orders of Insects
*
A Safrinet Manual for Entomology and Arachnology
SPC
Tree of Life Project
– Insecta
Insecta Movies

Insect Morphology
Overview of insect external and internal anatomy
Fossil Insect Database
International Palaeoentological Society
UF Book of Insect Records

InsectImages.org
24,000 high resolution insect photographs
BBC Nature:
Insect news, and video clips from BBC programmes past and present.
The Nature Explorers
Many insect video clips. {{Authority control

Insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

Entomology

Insects described in 1758 Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

Extant Early Devonian first appearances

Etymology

Definitions

Phylogeny and evolution

External phylogeny

Internal phylogeny

Taxonomy

Evolutionary relationships

Diversity

Morphology and physiology

External

Segmentation

Exoskeleton

Internal

Nervous system

Digestive system

= Foregut

= Midgut

= Hindgut

Excretory system

Reproductive system

Respiratory system

Circulatory system

Reproduction and development

Metamorphosis

Incomplete metamorphosis

Complete metamorphosis

Senses and communication

Light production and vision

Sound production and hearing

Chemical communication

Social behavior

Care of young

Locomotion

Flight

Walking

Swimming

Ecology

Defense and predation

Pollination

Parasitism

Relationship to humans

As pests

In beneficial roles

In research

As food

As feed

In other products

As pets

In culture

See also

Notes

References

External links