cocoon of the silkworm: Bombyx mori
A cocoon is a protective coil of silk produced from spinerets under the mouth of a caterpillar. It is wound round and around itself by the pupating caterpillar in a many species of moth. The caterpillars of butterflies do not make a cocoon.
When a Caterpillar is ready to change into a butterfly or moth, the animal forms a pupa, also commonly known as a chrysalis (plurals : pupae, chrysalids). The last instar of the caterpillar moults as usual but the next skin hardens rather than staying soft, so protecting the changing insect inside. For some species the pupa is attached to a little pad of silk by tiny hooks in the tail (cremaster):
Some species attach the pupa to a twig by the tail and a central girdle of silk:
Other species just have a naked pupa which lays loosely on the ground :
Some species of moth surround the pupa with a cocoon. Only certain moth species do this:
The silk thread of some species is very fine and is harvested to make silk cloth. Other species spin a cocoon around the pupa but it is tough and leathery and no use for making silk cloth :
Some species decorate the outside of the cocoon with debris to camouflage it :
This is especially true of the Caterpillars in the family PSYCHIDAE :
Some Caterpillars attach irritating hairs from their own skin to the outside of the cocoon making it hazardous to handle :
Some species burrow into the soil and pupate there.
Frequently Asked Questions about Caterpillars
(updated 21 February 2008)