Handbook of Insect Biology

Insects are numerous usually small arthropod animals of the class Insectahaving an adult stage characterized by three pairs of legs and a body segmentedinto head thorax and abdomen and usually having two pairs of wings. Insectsinclude the flies crickets mosquitoes beetles butterflies and bees. Like otherarthropods an insect has a hard outer covering or exoskeleton a segmentedbody and jointed legs. Adult insects typically have wings and are the onlyflying invertebrates. The body of the typical adult insect is divided into threedistinct parts the head thorax and abdomen. The exoskeleton is composedof a horny substance called chitin.