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Insects make up between half and 90% of all animal biodiversity, with over one million species described and estimates of up to 30 million. The oldest known insect fossil is from 396 million years ago, and the most primitive group is the order Archaeognatha. All other insects have wings, being part of the subclass Pterygota, which contains 32 orders and seven superorders.
Insects are the most diverse group of animals in existence. With over one million species described and estimates of the total species count ranging as high as 30 million, insects make up between half and 90% of all animal biodiversity. This is all the more impressive because insects aren’t even an animal phylum, they’re just a class within the phylum Arthropoda. The oldest known insect fossil is Rhyniognatha hirsti from the Devonian, about 396 million years old. Since then, insects have diversified, particularly since the emergence of flowering plants about 125 million years ago.
The most primitive group of insects is the order Archaeognatha (leaping bristletail), which has only about 300 species. Along with the order Thysanura (silverfish), these two orders are the only two within the class Insecta that have no wings. Other wingless animals formerly classified as insects, such as springtails, proturans, and diplurans are now considered basal lineages apart from Insecta, and are instead placed in their own class, Entognatha. Previously, all these wingless animals were called Apterygota, which means “without wings.”
All other insects have wings, being part of the subclass Pterygota. Previously, Pterygota was divided into the infraclasses Palaeoptera, or “old wing” and Neoptera, or “new wing”, but these categories are now suspected to be paraphyletic. This means that members of infraclasses may not be exclusive descendants of a common ancestor, and thus not a true clade. However, categorizations can be useful as a reference to body type. Paleoptera are insects that do not have the ability to fold their wings over their abdomen, while Neoptera can do so. The fossil record for Paleoptera is extensive, but today the group includes only two surviving orders: mayflies and dragonflies. Most other insects are Neopterans.
The Neoptera are a huge group, containing 32 orders, five of which are extinct. These orders are tentatively placed into seven superorders based on physiological characteristics and presumed common origins. Neoptera members include web spinners, angelic bugs, earwigs, grasshoppers, stick insects, ice crawlers, gladiators, beetles, termites, mantises, lice, thrips, lice, true bugs, ants, bees, wasps, cockroaches, winged parasites , snakeflies, alderflies, reticulated bugs, scorpionfish, fleas, snow fleas, flies, caddisflies, butterflies and moths.
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