Complete metamorphosis is the total change of an insect that goes through four distinct stages. Those stages are egg, larva, pupa and adult.
The time an insect spends in each stage varies depending on the insect. In the egg stage, the insect is an embryo waiting to hatch. During the larva stage, it hatches and usually begins to eat and grow. In most cases, insects look distinctly different now than they will in the final stage of metamorphosis. Caterpillars are the larva stage of butterflies.
After the larva finishes growing, it enters the pupa stage and forms a cocoon. There, it waits for its body to redevelop for the final stage when it becomes an adult.