the head carries

• one pair of antennae (crustaceans have two) which commonly support the sense of touch and something like 'smell'
• two compound eyes and, in most cases, one or more simple eyes
• three pairs of mouth parts, usually including mandibles and/or a siphon formed from one pair of the appendages
• a rudimentary brain

the thorax bears

• all three pairs of legs, which often include sensory organs for taste and/or touch
• zero, one, or two pairs of wings. Most insects have two pairs of wings (in the beetles the second pair is hardened to form a protective cover for the flying wings), but the Order Diptera has only one. Most orders include some wingless species or species with some members which are wingless (eg. the males of many ants in the order Hymenoptera. The larvae (grubs, maggots, caterpillars, etc.) of the completely metamorphosing insects do not have wings and the nymphs (terrestrial) and naiads (aquatic) of the incompletely metamorphosing insects have wing buds. Wings only appear in the final molt of the nymph or naiad to the adult form of the species.

the abdomen holds

• the breathing apparatus
• digestive system
• reproductive organs and, in the females of many species, an ovipositor for depositing eggs (eg. a wasp's sting)
• heart
• miscellaneous items (eg. poison glands and sacs in bees, noise-making air sacs in cicadas)

In addition to these features, most insects have hairs which are sensitive to such things as the movement of air, humidity, and temperature, as well as to direct contact.