Metamorphosis is complete, that is, the insect goes through four stages: egg, larva, pupa, and adult. The eggs, which hatch in 2 to 30 days, are usually laid on a plant that the larva (called a caterpillar) uses for food. Most caterpillars eat leaves. After the last of several molts the larva is transformed into a pupa with a hard, often sculptured outer integument, within which it changes to the adult form. The butterfly pupa is called a chrysalis, or chrysalid. Most chrysalids (unlike the pupae of most moths) are not enclosed in a cocoon; however, they are usually suspended from some object by a silken thread and may have a partial covering. Except in those species that winter in the pupa stage, the adult usually emerges from the integument in two or three weeks. Members of some species winter in the egg stage, others as larvae or adults. The adults of most species, however, live only about a month.