All insects have segmented bodies made up of many small sections. Insects have three major body divisions, the head, thorax and abdomen. Mouthparts, eyes and antennae are found on the head, while legs and wings grow from the thorax. In some insects these body divisions are easy to see. In others they are not so separate. The antennae, which are often long and carry sense organs for touch and smell. The head also has the usually large compound eyes and some ocelli or simple eyes. The head carries several pairs of mouthparts, which are very important in distinguishing the insect order. Some are adapted for biting, with two mandibles, and some are modified to form a tube for sucking the liquid food. The thorax has legs and wings. The legs have spines and claws. The thorax carries a pair of wings. The wings are often colored and may have hairs or scales.
The outer covering of the insect is strengthened on all or some parts of the body by a hard cuticle, which protects the body, gives it a shape and as an external skeleton or exoskeleton provides a fixture for the soft body parts. This strengthened skin or cuticle consists of chitin and sclerotin. These two substances together form a very hard and resistant, but very light structure which in the course of evolution has served a variety of functions. Finally the cuticle is covered by a waxy layer, which acts as water repellant.
This very resistant and powerful form of skin has, however, one great disadvantage. Once formed it can not be altered, that is, it can no longer grow. As the rest of the insect’s body grows, a new skin begins to form under the old one. When the insect molts, the old skin splits and the insect crawls out. The soft, new exoskeleton expands at first just like elastic, but once it has dried and hardened, it will not grow any longer. Some newly molted insects eat their old skins, other just leave them behind.