What is a cocoon?

Silk moth cocoons

What is a cocoon? A cocoon is the silk ‘sleeping bag’ some species of moths make before they pupate. A caterpillar creates the silken cocoon with a silk gland/spinneret that is located under its mouth. Butterfly caterpillars do not make cocoons. (Some people consider the nest that a few species of butterflies make before pupating – a cocoon.)

Polyphemus moth cocoon

Not all species of moths make cocoons. Some pupate in leaf litter and some pupate under the soil. Some make a leaf nest, not a ‘cocoon’ as most of us think of a cocoon.

A Tersa Sphinx Moth pupa, dug up from the top layer of soil near a pentas plant

All butterflies and moths go through four stages. Ova (egg), larva (caterpillar), pupa (pupa or chrysalis), and imago (adult. A moth pupa is called a pupa (singular = pupa and plural = pupae). A butterfly pupa is correctly called either a pupa or a chrysalis. A butterfly pupa/chrysalis is not called a cocoon. A moth pupa is not called a chrysalis.

Gulf Fritillary butterfly chrysalis

Cocoons that are used to make silk material contain about four thousand feet of one long silk strand.

It does not harm the pupa to cut the cocoon open and remove it, as long as the pupa is protected from predators and dehydration. If it is removed, it should be placed in a container where it can emerge and climb high to expand its wings.

A freshly pupated silk moth pupa was removed from its cocoon

Inside the cocoon is the moth pupa. Once the cocoon is finished, the caterpillar takes about three days to pupate. Changing from moth caterpillar to pupa is a longer process than changing from a butterfly caterpillar to chrysalis. Butterflies usually pupate within 24 hours.

A Cecropia moth caterpillar makes its cocoon

Butterflies and moths both pupate from caterpillar to pupa. A butterfly pupa is often called a chrysalis.

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