Insects
Insecta
Summary 8
Insects or Insecta (from Latin insectum, a calque of Greek ἔντομον , "cut into sections") are by far the largest group of hexapod invertebrates within the arthropod phylum. Definitions and circumscriptions vary; in one approach insects comprise a class within the Phylum Arthropoda. As the term is used here, it is synonymous with Ectognatha.
Phylogeny and evolution 9
Hexapoda (Insecta, Collembola, Diplura, Protura)
Crustacea (crabs, shrimp, isopods, etc.)
PauropodaDiplopoda (millipedes)
Chilopoda (centipedes)
SymphylaArachnida (spiders, scorpions, mites, ticks, etc.)
Eurypterida (sea scorpions: extinct)
Xiphosura (horseshoe crabs)
Pycnogonida (sea spiders)
†Trilobites (extinct)
A phylogenetic tree of the arthropods and related 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 Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled Miracrustacea within Crustaceans, now termed Pancrustacea.
Insects form a single clade, closely related to crustaceans and myriapods.
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.
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 insect fossil was considered to be the DevonianRhyniognatha hirsti, from the 396-million-year-old Rhynie chert. However, other analyses have disputed this placement, finding it to be more likely a myriapod.
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). 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.
Late 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 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.
The remarkably successful Hymenoptera appeared as long as 200 million years ago in the Triassic 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.
Archaeognatha (Hump-backed/jumping bristletails)
Zygentoma (silverfish, firebrats, fishmoths)
†BojophlebiidaeOdonatoptera (Dragonflies)
Panephemeroptera (Mayflies)
Zoraptera (Angel insects)
Dermaptera (earwigs)
Plecoptera (stoneflies)
Orthoptera (grasshoppers, crickets, katydids)
Mantodea (praying mantises)
Blattodea (cockroaches & termites)
Grylloblattodea (ice-crawlers)
Mantophasmatodea (gladiators)
Phasmatodea (Stick insects)
Embioptera (Web spinners)
Psocodea (Book lice, barklice & sucking lice)
Hemiptera (true bugs)
Thysanoptera (Thrips)
Hymenoptera (sawflies, wasps, bees, ants)
StrepsipteraColeoptera (Beetles)
RhaphidiopteraNeuroptera (Lacewings)
MegalopteraLepidoptera (Butterflies & moths)
Trichoptera (Caddisflies)
Diptera (True flies)
NannomecopteraMecoptera (scorpionflies)
Neomecoptera (winter scorpionflies)
Siphonaptera (Fleas)
A cladogram based on the works of Sroka, Staniczek & Bechly 2014, Prokop et al. 2017 & Wipfler et al. 2019.
Cladogram of living insect groups, with numbers of species in each group. The Apterygota, Palaeoptera, and Exopterygota are possibly paraphyletic groups.
Traditional morphology-based or appearance-based systematics have usually given the Hexapoda the rank of superclass, 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 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 consist of the primitively wingless order of the silverfish (Zygentoma). Archaeognatha make up the Monocondylia based on the shape of their mandibles, while Zygentoma and Pterygota are grouped together as Dicondylia. The Zygentoma themselves possibly are not monophyletic, with the family Lepidotrichidae 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 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 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 and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea. Phasmatodea and Embiidina have been suggested to form the Eukinolabia. Mantodea, Blattodea, and Isoptera are thought to form a monophyletic group termed Dictyoptera.
The Exopterygota likely are paraphyletic in regard to the Endopterygota. Matters that have incurred controversy include Strepsiptera and 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 Hymenoptera.
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.
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 organisms. Coevolution has led to the development of very specific mutualisms in such systems.
Taxonomy 8
Cladogram of living insect groups, with numbers of species in each group. The Apterygota, Palaeoptera, and Exopterygota are possibly paraphyletic groups.
Traditional morphology-based or appearance-based systematics have usually given the Hexapoda the rank of superclass, 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 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 consist of the primitively wingless order of the silverfish (Zygentoma). Archaeognatha make up the Monocondylia based on the shape of their mandibles, while Zygentoma and Pterygota are grouped together as Dicondylia. The Zygentoma themselves possibly are not monophyletic, with the family Lepidotrichidae 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 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 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 and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea. Phasmatodea and Embiidina have been suggested to form the Eukinolabia. Mantodea, Blattodea, and Isoptera are thought to form a monophyletic group termed Dictyoptera.
The Exopterygota likely are paraphyletic in regard to the Endopterygota. Matters that have incurred controversy include Strepsiptera and 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 Hymenoptera.
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.
Sources and Credits
- (c) Greg Lasley, some rights reserved (CC BY-NC), uploaded by Greg Lasley
- (c) Thomas Bresson, some rights reserved (CC BY), https://www.flickr.com/photos/computerhotline/3781347123/
- (c) Oleksandr K, some rights reserved (CC BY-SA), https://www.flickr.com/photos/155724623@N08/50139988271/
- (c) xulescu_g, some rights reserved (CC BY-SA), https://www.flickr.com/photos/59161444@N05/23573714718/
- (c) Danny Perez Photography, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/da100fotos/4944607328/
- (c) André Vielma Mansilla, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/100887988@N03/25413066541/
- (c) xulescu_g, some rights reserved (CC BY-SA), https://www.flickr.com/photos/59161444@N05/18492357690/
- Adapted by Greenpigeonsnaturelk from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Insect
- (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Insect
