WHAT HAPPENS INSIDE A COCOON?

How certain species of insects transform from crawling caterpillars to flying moths and butterflies

- SCOTT DUTFIELD

When a caterpillar is ready to finish crawling around and take flight with a new pair of wings, it embarks on a journey of transformation called metamorphosis. The process sees the once squishy, undulating body of a caterpillar (the larval stage of the order Lepidoptera, which includes the world's butterflies, moths and skippers) swapped out for the winged body of its adult form. It takes several weeks, and in some cases months, for some species of butterflies and moths to complete the transformation, known as holometabolous metamorphosis. This form of metamorphosis has four distinct stages in the insect's life cycle, including the egg, larva, pupa and adult stage. Hemimetabolous metamorphosis, on the other hand, is an incomplete or partial metamorphosis, whereby an insect, such as a dragonfly, will undergo a series of exoskeleton sheddings, called moults, to transform from juvenile nymph to winged adult.

The all-important pupa stage in a butterfly or moth's life cycle is where they undergo the greatest physical transformation. For moths, caterpillars secrete a liquid silk to wrap around their bodies to undergo the process of pupation. Butterfly caterpillars, however, do things slightly differently. They only spin a small silk pad, which they hang themselves from. While they hang, these caterpillars will shed their skin and grow a hardened shell called a chrysalis, inside which their bodies undergo pupation.