Why do butterflies start as caterpillars?

Butterflies start as caterpillars because the young stage and adult stage do different work. A caterpillar is shaped for eating leaves and growing fast. A butterfly is shaped for moving through the air, drinking nectar, finding mates, and laying eggs in good places.

Inside the chrysalis, the animal rebuilds itself. Some body parts break down while special groups of cells form wings, long legs, and a strawlike proboscis. It is the same living creature, but childhood and adulthood come with almost opposite equipment.