[3][4] The insects and springtails are very abundant and are some of the most important pollinators, basal consumers, scavengers/detritivores and micropredators in terrestrial environments.

Hexapods are named for their most distinctive feature: a three-part body plan with a consolidated thorax and three pairs of legs.

[7][8] The head is composed of a presegmental acron that usually bears eyes (absent in Protura and Diplura),[9] followed by six segments, all closely fused together, with the following appendages: The mouth lies between the fourth and fifth segments and is covered by a projection from the sixth, called the labrum (upper lip).

[14] As is typical of arthropods adapted to life on land, each leg has a single walking branch composed of five segments.

[18][19] The appendages on the abdomen are extremely reduced, restricted to the external genitalia and sometimes a pair of sensory cerci on the last segment.

[30] A 2002 molecular analysis suggests that the hexapods diverged from their sister group, the Anostraca (fairy shrimps), at around the start of the Silurian period 440 million years ago, coinciding with the appearance of vascular plants on land.

Several hypotheses about their internal relationships have been suggested over the years, with proturans as the sister group to the other hexapods and collembolans and diplurans belonging together in Antennomusculata as the latest suggestion:[32] The following cladogram is given by Kjer et al. (2016):[33] Collembola (springtails) Protura (coneheads) Diplura (two-pronged bristletails) Archaeognatha (jumping bristletails) Zygentoma (silverfish) Pterygota (winged insects) An incomplete possible insect fossil, Strudiella devonica, has been recovered from the Devonian period.