Insects or Insecta (from
Latin insectum) are by far the largest group
of hexapod invertebrates within the arthropod phylum. Definitions and
circumscriptions vary; usually, insects comprise a class within the
Phylum Arthropoda. As used here, the term is synonymous with
Ectognatha. Insects have a chitinous exoskeleton, a three-part body
(head, thorax and abdomen), three pairs of jointed legs, compound eyes
and one pair of antennae. The most diverse group of animals, they
include more than a million described species and represent more than
half of all known living organisms. The number of extant species
is estimated at between six and ten million, and potentially
represent over 90% of the animal life forms on Earth. Insects may
be found in nearly all environments, although only a small number of
species reside in the oceans, a habitat dominated by another arthropod
The life cycles of insects vary but most hatch from eggs. Insect
growth is constrained by the inelastic exoskeleton and development
involves a series of molts. The immature stages can differ from the
adults in structure, habit and habitat, and can include a passive
pupal stage in those groups that undergo four-stage metamorphosis (see
holometabolism). Insects that undergo three-stage metamorphosis lack a
pupal stage and adults develop through a series of nymphal stages.
The higher level relationship of the
Hexapoda is unclear. Fossilized
insects of enormous size have been found from the
including giant dragonflies with wingspans of 55 to 70 cm
(22–28 in). The most diverse insect groups appear to have
coevolved with flowering plants.
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. Insects are the only invertebrates to
have evolved flight. Many insects spend at least part of their lives
under water, with larval adaptations that include gills, and some
adult insects are aquatic and have adaptations for swimming. Some
species, such as water striders, are capable of walking on the surface
of water. Insects are mostly solitary, but some, such as certain bees,
ants and termites, are social and live in large, well-organized
colonies. Some insects, such as earwigs, show maternal care, guarding
their eggs and young. Insects can communicate with each other in a
variety of ways.
Male moths can sense the pheromones of female moths
over great distances. Other species communicate with sounds: crickets
stridulate, or rub their wings together, to attract a mate and repel
Lampyridae in the beetle order 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, in the case of termites,
the wood itself. A few parasitic species are pathogenic. Some insects
perform complex ecological roles; blow-flies, for example, help
consume carrion but also spread diseases.
Insect pollinators 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 (including
humans) would be devastated. Many other insects are considered
ecologically beneficial as predators and a few provide direct economic
benefit. Silkworms and bees have been used extensively by humans for
the production of silk and honey, respectively. In some cultures,
people eat the larvae or adults of certain insects.
Phylogeny and evolution
3.1 Evolutionary relationships
5 Morphology and physiology
5.3.1 Nervous system
5.3.2 Digestive system
5.3.3 Reproductive system
5.3.4 Respiratory system
5.3.5 Circulatory system
6 Reproduction and development
6.1.1 Incomplete metamorphosis
6.1.2 Complete metamorphosis
7 Senses and communication
7.1 Light production and vision
7.2 Sound production and hearing
7.3 Chemical communication
8 Social behavior
8.1 Care of young
9.2.1 Use in robotics
10.1 Defense and predation
11 Relationship to humans
11.1 As pests
11.2 In beneficial roles
11.3 In research
11.4 As food
11.5 In culture
12 See also
15 Further reading
16 External links
The word "insect" comes from the
Latin word insectum, meaning "with a
notched or divided body", or literally "cut into", from the neuter
singular perfect passive participle of insectare, "to cut into, to cut
up", from in- "into" and secare "to cut"; because insects appear
"cut into" three sections. A calque of Greek ἔντομον
[éntomon], "cut into sections",
Pliny the Elder
Pliny the Elder introduced the Latin
designation as a loan-translation of the Greek word ἔντομος
(éntomos) or "insect" (as in entomology), which was Aristotle's term
for this class of life, also in reference to their "notched" bodies.
"Insect" first appears documented in English in 1601 in Holland's
translation of Pliny. Translations of Aristotle's term also form the
usual word for "insect" in Welsh (trychfil, from trychu "to cut" and
Serbo-Croatian (zareznik, from rezati, "to cut"),
Russian (насекомое nasekomoje, from seč'/-sekat', "to cut"),
The precise definition of the taxon Insecta and the equivalent English
name "insect" varies; three alternative definitions are shown in the
Definition of Insecta
Insecta sensu lato
Diplura (two-pronged bristletails)
Archaeognatha (jumping bristletails)
Insecta sensu stricto
Pterygota (winged insects)
Insecta sensu strictissimo
In the broadest circumscription, Insecta sensu lato 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 winged 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. For the
purposes of this article, the middle definition is used; insects
consist of two wingless taxa,
Archaeognatha (jumping bristletails) and
Zygentoma (silverfish), plus the winged or secondarily wingless
Phylogeny and evolution
Evolution of insects
This section needs to be updated. Please update this article to
reflect recent events or newly available information. (July 2017)
Hexapoda (Insecta, Collembola, Diplura, Protura)
Crustacea (crabs, shrimp, isopods, etc.)
Arachnida (spiders, scorpions, mites, ticks, etc.)
Eurypterida (sea scorpions: extinct)
Xiphosura (horseshoe crabs)
Pycnogonida (sea spiders)
A phylogenetic tree of the arthropods and related groups
Evolution has produced enormous variety in insects. Pictured are some
possible shapes of antennae.
The evolutionary relationship of insects to other animal groups
Although traditionally grouped with millipedes and
centipedes—possibly on the basis of convergent adaptations to
terrestrialisation—evidence has emerged favoring closer
evolutionary ties with crustaceans. In the
insects, together with Entognatha, Remipedia, and Cephalocarida, make
up a natural clade labeled Miracrustacea.
Insects form a single clade, closely related to crustaceans and
Other terrestrial arthropods, such as centipedes, millipedes,
scorpions, and spiders, 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.
The higher-level phylogeny of the arthropods continues to be a matter
of debate and research. In 2008, researchers at Tufts University
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 oldest definitive
insect fossil is the
Rhyniognatha hirsti, from the
396-million-year-old Rhynie chert. It may have superficially resembled
a modern-day silverfish insect. This species already possessed
dicondylic mandibles (two articulations in the mandible), a feature
associated with winged insects, suggesting that wings may already have
evolved at this time. Thus, the first insects probably appeared
earlier, in the
Four super radiations of insects have occurred: beetles (evolved about
300 million years ago), flies (evolved about 250 million years ago),
and moths and wasps (evolved about 150 million years ago). These
four groups account for the majority of described species. The flies
and moths along with the fleas evolved from the Mecoptera.
The origins of insect flight 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.
Carboniferous and Early
Permian insect orders include both extant
groups, their stem groups, and a number of
Paleozoic groups, now
extinct. During this era, some giant dragonfly-like forms reached
wingspans of 55 to 70 cm (22 to 28 in), making them far
larger than any living insect. This gigantism may have been due to
higher atmospheric oxygen 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
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.
The remarkably successful
Hymenoptera appeared as long as 146 million
years ago in the
Cretaceous period, but achieved their wide diversity
more recently in the
Cenozoic era, which began 66 million years ago. A
number of highly successful insect groups evolved in conjunction with
flowering plants, a powerful illustration of coevolution.
Many modern insect genera developed during the Cenozoic. Insects from
this period on are often found preserved in amber, often in perfect
condition. The body plan, or morphology, of such specimens is thus
easily compared with modern species. The study of fossilized insects
is called paleoentomology.
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 piscivores. Through gradual
evolutionary change, insectivory 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 mimics. Over time, this has led to
complex groups of coevolved species. Conversely, some interactions
between plants and insects, like pollination, are beneficial to both
Coevolution has led to the development of very specific
mutualisms in such systems.
See also: Category:
Insect orders and Category:
Archaeognatha - 470
Blattodea – 3,684–4,000
Coleoptera – 360,000–400,000
Dermaptera – 1,816
Diptera – 152,956
Embioptera – 200–300
Hemiptera – 50,000–80,000
Hymenoptera – 115,000
Lepidoptera – 174,250
Mantodea – 2,200
Mecoptera – 481
Megaloptera – 250–300
Neuroptera – 5,000
Notoptera – 30
Orthoptera – 24,380
Phasmatodea – 2,500–3,300
Phthiraptera – 3,000–3,200
Plecoptera – 2,274
Psocoptera – 5,500
Raphidioptera – 210
Siphonaptera – 2,525
Strepsiptera – 596
Thysanoptera – 5,000
Trichoptera – 12,627
Zoraptera – 28
Cladogram of living insect groups, with numbers of species in each
group. The Apterygota, Palaeoptera, and
Exopterygota are possibly
Traditional morphology-based or appearance-based systematics have
usually given the
Hexapoda the rank of superclass,:180 and
identified four groups within it: insects (Ectognatha), springtails
(Collembola), Protura, and Diplura, the latter three being grouped
together as the
Entognatha 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 (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 have been shown to be
paraphyletic, so rather than using ranks like subclass, superorder,
and infraorder, 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
Insects can be divided into two groups historically treated as
subclasses: wingless insects, known as Apterygota, and winged insects,
known as Pterygota. The
Apterygota consist of the primitively wingless
order of the silverfish (Zygentoma).
Archaeognatha make up the
Monocondylia based on the shape of their mandibles, while Zygentoma
Pterygota are grouped together as Dicondylia. The Zygentoma
themselves possibly are not monophyletic, with the family
Lepidotrichidae being a sister group to the
the remaining Zygentoma).
Neoptera are the winged orders of insects
differentiated by the presence of hardened body parts called
sclerites, 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 and Paraneoptera) and
complete metamorphosis-based groups. It has proved difficult to
clarify the relationships between the orders in
of constant new findings calling for revision of the taxa. For
Paraneoptera have turned out to be more closely related
Endopterygota than to the rest of the Exopterygota. The recent
molecular finding that the traditional louse orders
Anoplura are derived from within
Psocoptera has led to the new taxon
Embiidina have been suggested to form
the Eukinolabia. Mantodea, Blattodea, and
Isoptera are thought to
form a monophyletic group termed Dictyoptera.
Exopterygota likely are paraphyletic in regard to the
Endopterygota. Matters that have incurred controversy include
Diptera grouped together as Halteria based on a
reduction of one of the wing pairs – a position not well-supported
in the entomological community. 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
The study of the classification or taxonomy of any insect is called
systematic entomology. If one works with a more specific order or even
a family, the term may also be made specific to that order or family,
for example systematic dipterology.
Though the true dimensions of species diversity remain uncertain,
estimates range from 2.6–7.8 million species with a mean of 5.5
A pie chart of described eukaryote species, showing just over half of
these to be insects
Between 950,000–1,000,000 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, and with only about 20,000 new species of all organisms being
described each year, most insect species likely will remain
undescribed, unless species descriptions greatly increase in rate. Of
the 24 orders of insects, four dominate in terms of numbers of
described species, with at least 670,000 species included in
Hymenoptera and Lepidoptera.
Comparison of the estimated number of species in the four most
speciose insect orders
Average description rate
(species per year)
A 2015 study estimated the number of beetle species at 0.9–2.1
million with a mean of 1.5 million.
Morphology and physiology
Insect morphology and
Thorax C- Abdomen
2. ocelli (lower)
3. ocelli (upper)
4. compound eye
5. brain (cerebral ganglia)
7. dorsal blood vessel
8. tracheal tubes (trunk with spiracle)
13. mid-gut (stomach)
14. dorsal tube (Heart)
16. hind-gut (intestine, rectum & anus)
19. nerve chord (abdominal ganglia)
20. Malpighian tubes
21. tarsal pads
27. fore-gut (crop, gizzard)
28. thoracic ganglion
30. salivary gland
31. subesophageal ganglion
Insects have segmented bodies supported by exoskeletons, 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 thorax and an abdomen. The head supports a pair of
sensory antennae, a pair of compound eyes, and, if present, one to
three simple eyes (or ocelli) and three sets of variously modified
appendages that form the mouthparts. The thorax has six segmented
legs—one pair each for the prothorax, mesothorax and the metathorax
segments making up the thorax—and, none, two or four wings. 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, excretory
and reproductive internal structures.:22–48 Considerable
variation and many adaptations in the body parts of insects occur,
especially wings, legs, antenna and mouthparts.
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
sclerites. Here, the vertex, or the apex (dorsal region), is
situated between the compound eyes for insects with a hypognathous and
opisthognathous head. In prognathous insects, the vertex is not found
between the compound eyes, but rather, where the ocelli 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.:13
The thorax is a tagma composed of three sections, the prothorax,
mesothorax and the metathorax. 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 dilineated 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 abdomen 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
The insect outer skeleton, the cuticle, is made up of two layers: the
epicuticle, which is a thin and waxy water resistant outer layer and
contains no chitin, and a lower layer called the procuticle. 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.:22–24 The exocuticle is greatly reduced in many
soft-bodied insects (e.g., caterpillars), especially during their
Insects are the only invertebrates to have developed active flight
capability, and this has played an important role in their
success.:186 Their 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 more efficient and allows more muscle connections;
crustaceans also use the same method, though all spiders use hydraulic
pressure to extend their legs, a system inherited from their
pre-arthropod ancestors. Unlike insects, though, most aquatic
crustaceans are biomineralized with calcium carbonate extracted from
The nervous system of an insect can be divided into a brain and a
ventral nerve cord. 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, called the
The thoracic 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 has only two in the thorax and three in
the abdomen. Some insects, like the house fly Musca domestica, have
all the body ganglia fused into a single large thoracic ganglion.
At least a few insects have nociceptors, cells that detect and
transmit signals responsible for the sensation of pain.[not in
citation given] This was discovered in 2003 by studying the variation
in reactions of larvae of the common fruitfly
Drosophila 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.
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 proteins, polysaccharides, fats and nucleic acids. These
macromolecules must be broken down by catabolic reactions into smaller
molecules like amino acids and simple sugars before being used by
cells of the body for energy, growth, or reproduction. This break-down
process is known as digestion.
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
The salivary glands (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 flies, 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.:31 The
gut is where almost all of insects' digestion takes place. It can be
divided into the foregut, midgut and hindgut.
Stylized diagram of insect digestive tract showing malpighian tubule,
from an insect of the order Orthoptera
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 proteins as protection from tough
food. The foregut includes the buccal cavity (mouth), pharynx,
esophagus and crop and proventriculus (any part may be highly
modified), which both store food and signify when to continue passing
onward to the midgut.:70
Digestion starts in buccal cavity (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 amylases),
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
Bumblebee defecating. Note the contraction of the abdomen to provide
Once food leaves the crop, it passes to the midgut (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.:32
In the hindgut (element 16 in numbered diagram), or proctodaeum,
undigested food particles are joined by uric acid 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. The uric acid is formed using
hemolymph waste products diffused from the Malpighian tubules (element
20). It is then emptied directly into the alimentary canal, at the
junction between the midgut and hindgut. The number of Malpighian
tubules possessed by a given insect varies between species, ranging
from only two tubules in some insects to over 100 tubules in
Insect reproductive system
The reproductive system of female insects consist of a pair of
ovaries, accessory glands, one or more spermathecae, and ducts
connecting these parts. The ovaries are made up of a number of egg
tubes, called ovarioles, 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 oothecae. Spermathecae are tubes or sacs in which sperm can be
stored between the time of mating and the time an egg is
For males, the reproductive system is the testis, suspended in the
body cavity by tracheae and the fat body. 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, which descend from the primordial pole
cells very early during embryogenesis.:885
The tube-like heart (green) of the mosquito
Anopheles gambiae extends
horizontally across the body, interlinked with the diamond-shaped wing
muscles (also green) and surrounded by pericardial cells (red). Blue
depicts cell nuclei.
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 (element 8 in
numbered diagram). Since oxygen is delivered directly, the circulatory
system is not used to carry oxygen, and is therefore greatly reduced.
The insect circulatory system has no veins or arteries, and instead
consists of little more than a single, perforated dorsal tube that
pulses peristaltically. Toward the thorax, the dorsal tube (element
14) divides into chambers and acts like the insect's heart. The
opposite end of the dorsal tube is like the aorta of the insect
circulating the hemolymph, arthropods' fluid analog of blood, inside
the body cavity.:61–65 Air is taken in through openings on
the sides of the abdomen called spiracles.
The respiratory system is an important factor that limits the size of
insects. As insects get bigger, this type of oxygen transport gets
less efficient and thus the heaviest insect currently weighs less than
100 g. However, with increased atmospheric oxygen levels, as
happened in the late Paleozoic, larger insects were possible, such as
dragonflies with wingspans of more than two feet.
There are many different patterns of gas exchange demonstrated by
different groups of insects.
Gas exchange patterns in insects can
range from continuous and diffusive ventilation, to discontinuous gas
exchange.:65–68 During continuous gas exchange, oxygen is taken
in and carbon dioxide 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 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.
The insect circulatory system utilizes hemolymph, a tissue analogous
to blood that circulates in the interior of the insect body, while
remaining in direct contact with the animal's tissues. It is composed
of plasma in which hemocytes are suspended. In addition to hemocytes,
the plasma also contains many chemicals. It is also the major tissue
type of the open circulatory system of arthropods, characteristic of
spiders, crustaceans and insects.
Reproduction and development
A pair of
Simosyrphus grandicornis hoverflies mating in flight.
A pair of grasshoppers mating.
The majority of insects hatch from eggs. The fertilization and
development takes place inside the egg, enclosed by a shell (chorion)
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. 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. 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, and thus gestate inside the
mother and are born alive.:129, 131, 134–135 Some insects, like
parasitic wasps, show polyembryony, where a single fertilized egg
divides into many and in some cases thousands of separate
embryos.:136–137 Insects may be univoltine, bivoltine or
multivoltine, i.e. they may have one, two or many broods (generations)
in a year.
The different forms of the male (top) and female (bottom) tussock moth
Orgyia recens is an example of sexual dimorphism in insects.
Other developmental and reproductive variations include haplodiploidy,
polymorphism, paedomorphosis or peramorphosis, sexual dimorphism,
parthenogenesis and more rarely hermaphroditism.:143 In
haplodiploidy, which is a type of sex-determination system, the
offspring's sex is determined by the number of sets of chromosomes 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 phenotypes 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 as an
exemplar of sexual dimorphism in insects.
Some insects use parthenogenesis, a process in which the female can
reproduce and give birth without having the eggs fertilized by a male.
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.
More rarely, some insects display hermaphroditism, in which a given
individual has both male and female reproductive organs.
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. Still other insects have evolved
mechanisms of diapause that allow eggs or pupae to survive these
Metamorphosis in insects is the biological process of development all
insects must undergo. There are two forms of metamorphosis: incomplete
metamorphosis and complete metamorphosis.
Main article: Hemimetabolism
Hemimetabolous 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 epicuticle 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
Immature insects that go through incomplete metamorphosis are called
nymphs or in the case of dragonflies and damselflies, also naiads.
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.
This southern hawker dragonfly molts its exoskeleton several times
during its life as a nymph; shown is the final molt to become a winged
Main article: Holometabolism
Gulf fritillary life cycle, an example of holometabolism.
Holometabolism, or complete metamorphosis, is where the insect changes
in four stages, an egg or embryo, a larva, a pupa and the adult or
imago. In these species, an egg hatches to produce a larva, 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 pupa, 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.:151 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.
Some of the oldest and most successful insect groups, such
Endopterygota, use a system of complete metamorphosis.:143
Complete metamorphosis is unique to a group of certain insect orders
Lepidoptera and Hymenoptera. This form of
development is exclusive and not seen in any other arthropods.
Senses and communication
Many insects possess very sensitive and, or specialized organs of
perception. Some insects such as bees can perceive ultraviolet
wavelengths, or detect polarized light, while the antennae of male
moths can detect the pheromones of female moths over distances of many
kilometers. The yellow paper wasp (Polistes versicolor) 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, 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 emissions of bats, which helps them avoid
predation.:87–94 Insects that feed on blood have special sensory
structures that can detect infrared 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 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
Most insects have compound eyes and two antennae.
A few insects, such as members of the families Poduridae and
Mycetophilidae (Diptera) and the beetle
families Lampyridae, Phengodidae,
bioluminescent. The most familiar group are the fireflies, 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 (Mycetophilidae, fungus gnats) glow to
lure small flying insects into sticky strands of silk. Some
fireflies of the genus Photuris mimic the flashing of female Photinus
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, are able to
perceive light and dark. Many species have acute vision capable of
detecting minute movements. The eyes may include simple eyes or ocelli
as well as compound eyes of varying sizes. Many species are able to
detect light in the infrared, ultraviolet and the visible light
wavelengths. Color vision has been demonstrated in many species and
phylogenetic analysis suggests that UV-green-blue trichromacy existed
from at least the
Devonian period between 416 and 359 million years
Sound production and hearing
Insects were the earliest organisms to produce and sense sounds.
Insects make sounds mostly by mechanical action of appendages. In
grasshoppers and crickets, this is achieved by stridulation. Cicadas
make the loudest sounds among the insects by producing and amplifying
sounds with special modifications to their body to form tymbals and
associated musculature. The African cicada
Brevisana brevis has been
measured at 106.7 decibels at a distance of 50 cm
(20 in). Some insects, such as the
Helicoverpa zea moths,
hawk moths and Hedylid butterflies, can hear ultrasound 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 mimic 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.
Several unidentified grasshoppers stridulating
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Very low sounds are also produced in various species of Coleoptera,
Mantodea 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 organs 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 vibrations transmitted through
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), 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 Nezara viridula. Vibrations can also be used to communicate
between entirely different species; lycaenid (gossamer-winged
butterfly) caterpillars, which are myrmecophilous (living in a
mutualistic association with ants) communicate with ants in this
Madagascar hissing cockroach
Madagascar hissing cockroach has the ability to press air
through its spiracles to make a hissing noise as a sign of
aggression; the death's-head hawkmoth 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 in close
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
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
chemicals, termed semiochemicals, are often derived from plant
metabolites include those meant to attract, repel and provide other
kinds of information. Pheromones, a type of semiochemical, are used
for attracting mates of the opposite sex, for aggregating conspecific
individuals of both sexes, for deterring other individuals from
approaching, to mark a trail, and to trigger aggression in nearby
individuals. Allomones benefit their producer by the effect they have
upon the receiver. Kairomones 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 known to have developed in social insects.:96–105
A cathedral mound created by termites (Isoptera).
Social insects, such as termites, ants and many bees and wasps, are
the most familiar species of eusocial animal. 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 superorganisms. It is sometimes argued that the various
species of honey bee 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.:309–311 Though
perhaps not as advanced as honey bees, bumblebees also potentially
have some social communication behaviors. Bombus terrestris, for
example, exhibit a faster learning curve for visiting unfamiliar, yet
rewarding flowers, when they can see a conspecific foraging on the
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, 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).:14
Care of young
The eusocial insects build nest, guard eggs, and provide food for
offspring full-time (see Eusociality). 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, 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.
Insect flight and
White-lined sphinx moth feeding in flight
Basic motion of the insect wing in insect with an indirect flight
mechanism scheme of dorsoventral cut through a thorax segment with
c dorsoventral muscles
d longitudinal muscles.
Insects are the only group of invertebrates to have developed flight.
The evolution of insect wings has been a subject of debate. Some
entomologists suggest that the wings are from paranotal lobes, or
extensions from the insect's exoskeleton called the nota, 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
Carboniferous age, some of the
Meganeura dragonflies had as much
as a 50 cm (20 in) 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 and include several moth species
such as the
Atlas moth and the white witch (Thysania agrippina).
Insect flight has been a topic of great interest in aerodynamics 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, and the misconception that physics says "bumblebees can't fly"
persisted throughout most of the twentieth century.
Unlike birds, many small insects are swept along by the prevailing
winds although many of the larger insects are known to make
migrations. Aphids are known to be transported long distances by
low-level jet streams. As such, fine line patterns associated
with converging winds within weather radar imagery, like the WSR-88D
radar network, often represent large groups of insects.
Spatial and temporal stepping pattern of walking desert ants
performing an alternating tripod gait. Recording rate: 500 fps,
Playback rate: 10 fps.
Many adult insects use six legs for walking and have adopted a
tripedal gait. The tripedal gait allows for rapid walking while always
having a stable stance and has been studied extensively in cockroaches
and ants. The legs are used in alternate triangles touching the
ground. 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 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.
Use in robotics
Robot locomotion and Hexapod (robotics)
Insect walking is of particular interest as an alternative form of
locomotion in robots. The study of insects and bipeds has a
significant impact on possible robotic methods of transport. This may
allow new robots to be designed that can traverse terrain that robots
with wheels may be unable to handle.
Main article: Aquatic insects
Notonecta glauca underwater, showing its paddle-like
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 beetles, 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
Dragonfly naiads use jet propulsion, forcibly
expelling water out of their rectal chamber. Some species like
the water striders 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
Stenus 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 term
Insect ecology is the scientific study of how insects, individually or
as a community, interact with the surrounding environment or
ecosystem.:3 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 beetles, which are scavengers that feed
on dead animals and fallen trees and thereby recycle biological
materials into forms found useful by other organisms. These
insects, and others, are responsible for much of the process by which
topsoil is created.:3, 218–228
Defense and predation
See also: Defense in insects
Perhaps one of the most well-known examples of mimicry, the viceroy
butterfly (top) appears very similar to the noxious-tasting monarch
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 and parasitism. Insects then have a variety of defense
strategies to avoid being attacked by predators or parasitoids. These
include camouflage, mimicry, toxicity and active defense.
Camouflage 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 beetles (family Chrysomelidae) or weevils. 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. Some
species have the ability to change color as their surroundings shift
(B. scabrinota, T. californica). 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), where the insect
enters a motionless state that can be maintained for a long period.
The nocturnal feeding habits of adults also aids
remaining concealed from predators.
Another defense that often uses color or shape to deceive potential
enemies is mimicry. A number of longhorn beetles (family Cerambycidae)
bear a striking resemblance to wasps, 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 and is most commonly known by the mimicry by the limenitidine
viceroy butterfly of the inedible danaine monarch. Later research has
discovered that the viceroy is, in fact more toxic than the monarch
and this resemblance should be considered as 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
Taxa from the toxic genus
Heliconius 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
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 beetles of the family Carabidae can spray
chemicals from their abdomen with great accuracy, to repel
See also: Pollination
European honey bee
European honey bee carrying pollen in a pollen basket back to the hive
Pollination is the process by which pollen is transferred in the
reproduction of plants, thereby enabling fertilisation and sexual
reproduction. 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 syndromes. These arose
through complex plant-animal adaptations. Pollinators find flowers
through bright colorations, including ultraviolet, and attractant
pheromones. The study of pollination by insects is known as
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 and yellow fever and because of such,
mosquitoes indirectly cause more deaths of humans than any other
Relationship to humans
See also: Pest insect
Aedes aegypti, a parasite, is the vector of dengue fever and yellow
Many insects are considered pests by humans. Insects commonly regarded
as pests include those that are parasitic (e.g. lice, bed bugs),
transmit diseases (mosquitoes, flies), damage structures (termites),
or destroy agricultural goods (locusts, weevils). 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
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's use exemplifies how some
insecticides can threaten wildlife beyond intended populations of pest
In beneficial roles
Economic entomology § Beneficial insects
Because they help flowering plants to cross-pollinate, some insects
are critical to agriculture. This
European honey bee
European honey bee is gathering
nectar while pollen collects on its body.
A robberfly with its prey, a hoverfly.
such as these help control insect populations.
Although pest insects attract the most attention, many insects are
beneficial to the environment and to humans. Some insects, like wasps,
bees, butterflies and ants, pollinate flowering plants.
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. 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 in order to have sufficient pollinators in
the field, orchard or greenhouse at bloom time.:240–243 Another
solution, as shown in Delaware, has been to raise native plants to
help support native pollinators like L. vierecki. Insects also
produce useful substances such as honey, wax, lacquer and silk. Honey
bees have been cultured by humans for thousands of years for honey,
although contracting for crop pollination is becoming more significant
for beekeepers. The silkworm has greatly affected human history, as
silk-driven trade established relationships between
China and the rest
of the world.
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, aphids feed on crops
and cause problems for farmers, but ladybugs feed on aphids, and can
be used as a means to get significantly reduce pest aphid populations.
While birds 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
Insects are also used in medicine, for example fly larvae (maggots)
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.
The common fruitfly
Drosophila melanogaster is one of the most widely
used organisms in biological research.
Insects play important roles in biological research. For example,
because of its small size, short generation time and high fecundity,
the common fruit fly
Drosophila melanogaster is a model organism for
studies in the genetics of higher eukaryotes. D. melanogaster has been
an essential part of studies into principles like genetic linkage,
interactions between genes, chromosomal genetics, development,
behavior and evolution. Because genetic systems are well conserved
among eukaryotes, understanding basic cellular processes like DNA
replication or transcription in fruit flies can help to understand
those processes in other eukaryotes, including humans. The genome
of D. melanogaster was sequenced 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
Main article: Entomophagy
In some cultures, insects, especially deep-fried cicadas, are
considered to be delicacies, whereas in other places they form part of
the normal diet. Insects have a high protein content for their mass,
and some authors suggest their potential as a major source of protein
in human nutrition.:10–13 In most first-world countries,
however, entomophagy (the eating of insects), is taboo. Since it
is impossible to entirely eliminate pest insects from the human food
chain, insects are inadvertently present in many foods, especially
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, the eating of insects is
taboo in cultures that have other protein sources such as fish or
Due to the abundance of insects and a worldwide concern of food
shortages, the Food and
Agriculture Organisation of the United Nations
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.
Main article: Insects in culture
Scarab beetles held religious and cultural symbolism in Old Egypt,
Greece and some shamanistic Old World cultures. The ancient Chinese
regarded cicadas as symbols of rebirth or immortality. In Mesopotamian
literature, the epic poem of
Gilgamesh has allusions to
signify the impossibility of immortality. Among the Aborigines of
Australia of the
Arrernte language groups, honey ants and witchety
grubs served as personal clan totems. In the case of the 'San'
bush-men of the Kalahari, it is the praying mantis that holds much
cultural significance including creation and zen-like patience in
Book: Introduction to Insects
Defense in insects
Flying and gliding animals
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Extant Arthropoda classes by subphylum
Pycnogonida (sea spiders)
Merostomata (horseshoe crabs)¹
Arachnida (spiders, scorpions, ticks, mites)
Symphyla (symphylans or garden centipedes)
Ostracoda (seed shrimps)
Pentastomida (tongue worms)
Branchiura (fish lice)
Malacostraca (woodlice, shrimps, crayfish, lobsters, crabs)
Thecostraca (barnacles and relatives) + Tantulocarida
Cephalocarida (horseshoe shrimps)
Branchiopoda (fairy, tadpole, clam shrimps, water fleas)
Diplura (two-pronged bristletails)³
¹contains the only extant order Xiphosura
italic are paraphyletic groups
Sources: Edgecombe et al. (2014), Petrunina (2012) for pancrustaceans.
Archaeognatha (jumping bristletails)
Thysanura (Zygentoma) (silverfish, firebrats)
Odonata (dragonflies, damselflies)
Phasmatodea (stick and leaf insects)
Notoptera (ice-crawlers, gladiators)
Orthoptera (crickets, wetas, grasshoppers, locusts)
Zoraptera (angel insects)
Blattodea (cockroaches, termites)
Psocodea (barklice, lice)
Hemiptera (cicadas, aphids, true bugs)
Hymenoptera (sawflies, wasps, ants, bees)
Strepsiptera (twisted-winged parasites)
Megaloptera (alderflies, dobsonflies, fishflies)
Neuroptera (net-winged insects: lacewings, mantidflies, antlions)
Mecoptera (scorpionflies) +
Diptera (gnats, mosquitoes, flies)
Lepidoptera (moths, butterflies)
Four most speciose orders are marked in bold
Italic are paraphyletic groups
Based on Sasaki et al. (2013)
Extinct incertae sedis families and genera are marked in italic
Insects in culture
In the arts
Insects in art
Insects in film
Insects in literature
Insects in music
List of insect-inspired songs
Insects on stamps
Insects in religion
Colorado potato beetle
Cottony cushion scale
Western corn rootworm
Insect bites and stings
Insect sting allergy
House longhorn beetle
Home-stored product entomology
Alfred Russel Wallace
Hans Zinsser (Rats,
Lice and History)
Lafcadio Hearn (
Living things in culture
Fauna Europaea: 4
BNF: cb11932119n (d