Why is the butterfly born twice?

The butterfly has two distinct stages in its life. It comes out of the egg as a caterpillar which feeds on leaves voraciously and becomes plump. The caterpillar then spins a covering around itself which is called a cocoon. One can see the cocoon hanging from the underside of leaves in some plants. After undergoing some changes — a process called metamorphosis —within the cocoon, the caterpillar comes out as a beautiful butterfly!