Butterflies are insects. Adult butterflies have large, often brightly colored wings, and conspicuous, fluttering flight. Butterfly fossils date to the Paleocene, about 56 million years ago. They have a four-stage life cycle, as like most insects they undergo complete metamorphosis. Winged adults lay eggs on the food plant on which their larvae, known as caterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed, pupate in a chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out, and after its wings have expanded and dried, it flies off.

Source: Wikipedia