Butterflies go through a life cycle that involves several stages: egg, larva, pupa, and adult. The from a caterpillar into a butterfly occurs during the pupa stage. During this stage, the caterpillar's old body dies and a new body forms inside a protective shell known as a chrysalis.
Moth caterpillars and many other insect larvae spin silk coverings for the chrysalis. These silk casings are called cocoons. Cocoons can be soft or hard, solid or web-like and any of several different colors or even see-through.
Cocoons provide camouflage and additional protection for the chrysalis. Many moth caterpillars will spin their cocoons in concealed locations, such as the underside of leaves, at the base of a tree, or hanging from a small branch.
While some people think of cocoons as a resting place, there's no resting going on inside the cocoon! To the contrary, there's a lot of activity. Inside the cocoon and the chrysalis, the caterpillar is transforming into a new creature. This requires that the old caterpillar body be broken down and turned into something new. Think of it as insect recycling!
The fluid breaks down the old caterpillar body into cells called imaginal cells. Imaginal cells are undifferentiated cells, which means they can become any type of cell. Many of these imaginal cells are used to form the new body.
The process of transformation within the chrysalis is known as . Although it varies by species, the whole process usually takes about two weeks. In some species, though, the process can take months if they stay inside the chrysalis to survive cold winter weather.
Insects that spin cocoons must eventually escape from them to complete their transformation. Some escape by cutting their way out from the inside. Others may secrete fluids that soften the cocoon and make it easier to escape.