Why do caterpillars grow so fast before becoming butterflies or moths?

Caterpillars grow fast because their main job is to eat, molt, and accumulate the resources needed for metamorphosis. Unlike adults, which often focus on reproduction, larvae are specialized for feeding and growth. As they shed their exoskeleton, they can increase in size dramatically over a short time. Hormones such as ecdysone and juvenile hormone control when they molt and eventually transform. This strategy is why many moth and butterfly species spend most of their life cycle as caterpillars rather than adults.