Parts of a Caterpillar
Caterpillars are the larvae of insects of the order Lepidoptera--butterflies and moths. These insects are holometabolous, meaning they undergo complete metamorphosis. Because the larvae of these insects is so different form the adult, both in anatomy and lifestyle, they are given different names. Other insects in which the larvae have their own names include flies (maggots) and beetles (grubs).
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Bodies
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Although immature, caterpillars follow the basic insect structure of having three parts: head, thorax and abdomen. But the caterpillar body as a whole is quite different from that of an adult moth or butterfly. It doen't have wings and its parts are much less defined. Instead of three clearly distinguishable sections, the caterpillar's body resembles a series of beads strung together.
Head
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Located at the anterior end, the head bears the sense organs, as well as the mouth and the mouth parts, which are appendages that specialize in handling food and can vary widely in form and function depending on the insect's lifestyle. Among the sense organs are the ocelli, which are light-sensitive spots and not true eyes like those found in adults, and the antennae, which are the organs of smell.
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Thorax
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As in the adult, the thorax consists of three segments, but in caterpillars it does not bear wings. Each thoracic segment has a pair of true legs, meaning that, like in an adult, they are divided into segments and have joints. The legs end in hook-like structures that enable the caterpillars to hold on firmly to the leaves where they live and which are their main food source.
Abdomen
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The abdomen comprises 10 segments. Some of these segments bear short prolegs, generally hooked on the end. They are called prolegs because they are not considered true legs like the segmented, jointed kind found in adults. Basically, they are stumps that aid the animal in locomotion and adhesion. It is believed that insect ancestors did possess legs in these segments but that they have been lost through evolution.
Mouth Parts
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Adult moths and butterflies have what are called "sucking" mouth parts that they use to feed on nectar. They are delicate and long and can reach deep into flowers. In contrast, caterpillars possess chewing mouth parts ideal for their diet of green leaves. These mouth parts are stubby and very tough. The fact that adults and larvae do not use the same food source is important because it allows them to avoid competition between generations.
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