The larval stage of butterflies, known as a caterpillar, emerges from the egg fully formed. Caterpillars see by means of groups of tiny eyes on each side of their head. The body of many species is protected by bristly hairs. Caterpillars have as many as eight pairs of appendages. Three pairs are true legs, and become the legs of the adult butterfly. These are located on the thorax behind the head. Another four pairs of appendages occur on the abdomen, and are known as false, or prolegs. There is also a single pair of claspers at the tip of the abdomen, which grip tightly to the food plant. Prolegs and claspers also carry tiny hooks, which catch a silk thread spun by the larva as it moves about its food plant and help keep it from falling. The silk thread is produced as a thick liquid, excreted through glands near the mouth, which is then spun into a thread by a spinneret located behind the jaws.
Caterpillars spend most of their time eating. Their large jaws (the mandibles) move sideways while shredding their plant diet. Caterpillars munch their way through life: first eating their egg shell, from which important nutrients are retrieved, and then continuously consuming its food plants. A very small number of butterfly species have caterpillars that are predators that feed on other insects. Caterpillars typically eat more than twice their own weight each day, pausing only to shed their old skin, in order that they may grow larger. Skin shedding (molting, or ecdysis) occurs at least four times before the caterpillar is fully grown. Growth rate depends on temperature; it is faster in warm weather, and slower when cool. Caterpillars seek a protected place in which to pupate, forming a protective shell and becoming dormant. Some caterpillars travel rather long distances (330 ft or 100 m) when seeking a sheltered place to pupate.