Thysanura (bristletails, silverfish; class Insecta, subclass Apterygota) One of the two orders of the Apterygota, whose name is derived from the Greek thysanos, ‘fringe’, and oura, ‘tail’, comprising ectognathous insects which are more or less flattened and adapted for running. The tapering body, usually less than 10 mm long, may be bare or covered with silvery scales; it is sometimes pigmented; and ends in three-segmented, bristle-like appendages. Ocelli are absent in most species, and the compound eyes are reduced or absent, and never contiguous as in the Archaeognatha. The mandibles are dicondylar, and the maxillary palps are five-segmented. The thorax is not arched, and the coxae lack styles, although they are present on most abdominal segments. Most species are free-living and very agile, with sexual and parthenogenetic reproduction. Post-embryonic development may be slow, or take as little as 2–3 months, and the reproductive potential is great. Thysanurans live in damp habitats, e.g. leaf-litter and rocky shores. One family, the Nicolettidae, are cavernicolous (cave-dwelling) and herbivorous, Several species are found in human habitations, where they feed on scraps, carbohydrate and dextrin compounds, and glue and sizes. Distributed throughout the world, and more diverse than the Archaeognatha, some are of economic importance. Lepismodes inquilinus (firebrat) inhabits warm buildings, where Lepisma saccharina (silverfish) also occurs, often inhabiting damp books. There are five families, with 330 species. See also LEPISMATOIDEA; MACHILOIDEA.

Thysanura An order of medium-sized wingless insects traditionally placed in the subclass Apterygota and comprising the bristletails and silverfish. These typically have slender bodies with long threadlike antenna and a segmented tail-like extension to the abdomen bordered on either side by the elongated paired cerci. The 350 or so species of bristletails are mostly nocturnal, feeding on algae, lichens, and other plant material and sheltering in litter or beneath bark during the day. They can spring some distance by arching the thorax and flexing the abdomen. The other major group includes the silverfish and firebrats, which comprise about 370 species. These are mostly detritivores living in litter or under bark, although some species are found in deserts and others are familiar inhabitants of human dwellings. These domestic species feed on food debris, paper, cotton, and similar materials. Some authorities now place the bristletails in a separate order, the Archaeognatha.