Caterpillars have short antennae and several simple eyes. The mouthparts are adapted for chewing with powerful mandibles and a pair maxillae, each with a segmented palp. Adjoining these is the labium-hypopharynx which houses a tubular spinneret which is able to extrude silk. Caterpillars such as those in the genus Calpodes (family Hesperiidae) have a specialized tracheal system on the 8th segment that function as a primitive lung. Butterfly caterpillars have three pairs of true legs on the thoracic segments and up to six pairs of prolegs arising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that are engaged hydrostatically and help the caterpillar grip the substrate. The epidermis bears tufts of setae, the position and number of which help in identifying the species. There is also decoration in the form of hairs, wart-like protuberances, horn-like protuberances and spines. Internally, most of the body cavity is taken up by the gut, but there may also be large silk glands, and special glands which secrete distasteful or toxic substances. The developing wings are present in later stage instars and the gonads start development in the egg stage.
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