What are a Cocoon and a Chrysalis?
  
Don Herbison-Evans,
( donherbisonevans@outlook.com)
and
Stella Crossley


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):


pupa of Danaus plexippus

Some species attach the pupa to a twig by the tail and a central girdle of silk:


pupa of Papilio aegeus

Other species just have a naked pupa which lays loosely on the ground :


pupae of Heteronympa merope

Some species of moth surround the pupa with a cocoon. Only certain moth species do this:


opened cocoon of Chelepteryx collesi showing the pupa inside

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 :


cocoon of Anthela acuta

Some species decorate the outside of the cocoon with debris to camouflage it :


two cocoons of Uraba lugens, one partly opened showing the brown pupa inside

This is especially true of the Caterpillars in the family PSYCHIDAE :


opened case of pupated Metura elongatus

Some Caterpillars attach irritating hairs from their own skin to the outside of the cocoon making it hazardous to handle :


cocoon of Chelepteryx collesi

Some species burrow into the soil and pupate there.


empty pupal skin of Trictena atripalpis left sticking out of the ground after the moth has emerged and flown away.

Link to
Frequently Asked Questions about Caterpillars

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(updated 21 February 2008)