Insect | |
---|---|
![]() | |
Clockwise from top left: dance fly (Empis livida), long-nosed weevil (Rhinotia hemistictus), mole cricket (Gryllotalpa brachyptera), German wasp (Vespula germanica), emperor gum moth (Opodiphthera eucalypti), assassin bug (Harpactorinae) | |
A chorus of several Magicicada species | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Clade: | Pancrustacea |
Subphylum: | Hexapoda |
Class: | Insecta Linnaeus, 1758 |
Subgroups | |
Synonyms | |
|
Insects<
See text. | |
---|---|
Synonyms | |
|
Insects or Insecta (from Latin insectum) are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; usually, insects comprise a class within the Arthropoda. As used here, the term Insecta 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. Insects are the most diverse group of animals; they include more than a million described species and represent more than half of all known living organisms.[2][3] The total number of extant species is estimated at between six and ten million;[2][4][5] potentially over 90% of the animal life forms on Earth are insects.[5][6] 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, crustaceans.
Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages often differ from the adults in structure, habit and habitat, and can include a passive pupal 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.[7] The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm (22 to 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, composed of the front and rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, and all flying insects derive from one common ancestor. 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 other males. Lampyrid beetles 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, and may vector diseases. 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 would be devastated.[8] Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey 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.[9][10] Human activities also have effects on insect biodiversity.
Insects or Insecta (from Latin insectum) are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; usually, insects comprise a class within the Arthropoda. As used here, the term Insecta 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. Insects are the most diverse group of animals; they include more than a million described species and represent more than half of all known living organisms.[2][3] The total number of extant species is estimated at between six and ten million;[2][4][5] potentially over 90% of the animal life forms on Earth are insects.[5][6] 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, crustaceans.
Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages often differ from the ad
Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages often differ from the adults in structure, habit and habitat, and can include a passive pupal 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.[7] The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm (22 to 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, composed of the front and rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, and all flying insects derive from one common ancestor. 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 other males. Lampyrid beetles 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, and may vector diseases. 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 would be devastated.[8] Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey 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.[9][10] Human activities also have effects on insect biodiversity.
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";[11] because insects appear "cut into" three sections. A calque of Greek ἔντομον [éntomon], "cut into sections", 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 mil, "animal"), Serbo-Croatian (zareznik, from rezati, "to cut"), Russian (насекомое nasekomoje, from seč'/-sekat', "to cut"), etc.[11][12]
The precise definition of the taxon Insecta and the equivalent English name "insect" varies; three alternative definitions are shown in the table.
Group | Alternative definitions | ||
---|---|---|---|
Collembola (springtails) | Insecta sensu lato =Hexapoda |
Entognatha (paraphyletic) |
Apterygota (wingless hexapods) (paraphyletic) |
Protura (coneheads) | |||
Diplura (two-pronged bristletails) | |||
Archaeognatha (jumping bristletails) | Insecta sensu stricto =Ectognatha | ||
Zygentoma (silverfish) | |||
Pterygota (winged insects) | Insecta sensu strictissimo |
In the broadest circumscription, Insecta sensu lato consists of all hexapods.[13][14] Traditionally, insects defined in this way were divided into "Apterygota" (the first five groups in the table)—the wingless insects—and Pterygota—the winged and secondarily wingless insects.[15] However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic,[16] 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.[13][16] 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.[17] 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 Pterygota.
![]() | This section needs to be updated. Please update this article to reflect recent events or newly available information. (July 2017) |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Diplopoda (millipedes) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Chilopoda (centipedes) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Diplopoda (millipedes) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Chilopoda (centipedes) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Eurypterida (sea scorpions: extinct)
Xiphosura (horseshoe crabs)
Xiphosura (horseshoe crabs)
Pycnogonida (sea spiders)
A A phylogenetic tree of the arthropods and related groups[18]
Although traditionally grouped with millipedes and centipedes—possibly on the basis of convergent adaptations to terrestrialisation[19]—evidence has emerged favoring closer evolutionary ties with crustaceans. In the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled millipedes and centipedes—possibly on the basis of convergent adaptations to terrestrialisation[19]—evidence has emerged favoring closer evolutionary ties with crustaceans. In the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled Miracrustacea.[20]
Insects form a single clade, closely related to crustaceans and myriapods.[21]
Other terrestrial arthropods, such as centipedes, millipedes, scorpions, spiders, woodlice, mites, and ticks 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.[22]
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.[23] The oldest definitive insect fossil is the Devonian 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 Silurian period.[1][24]
Four super radiations of insects have occurred: beetles (from about 300 million years ago), flies (from about 250 million years ago), moths and wasps (both from about 150 million years ago).[25] 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.[26]
Late Carboniferous and Early Permian insect orders include both extant groups, their stem groups,[27] 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 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.[28]
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.[29]
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.
Archaeognatha (Hump-backed/jumping bristletails)
Zygentoma (silverfish, firebrats, fishmoths) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Paranotalia | Zygentoma (silverfish, firebrats, fishmoths) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Paranotalia |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Embioptera (Web spinners)
Hemiptera (true bugs) | |
Thysanoptera (Thrips) | |
Thysanoptera (Thrips) | |
Thysanoptera (Thrips)
Neuropteriforma |
| ||||||||||||||||||||
Neuropterida |
| ||||||||||||||||||||
Lepidoptera (Butterflies & moths) | |||||||||||||||||||||
Trichoptera (Caddisflies) | |||||||||||||||||||||
Diptera (True flies) | |
Trichoptera (Caddisflies) | |
| |||||||||||||
A cladogram based on the works of Sroka, Staniczek & Bechly 2014,[30] Prokop et al. 2017[31] & Wipfler et al. 2019.[32] |