Cocoons Kept Over the Winter Need Cold Temperatures

Caterpillars are frequently collected by children, parents, teachers or other people interested in observing the change from caterpillar to cocoon to adult butterfly or moth. Most caterpillars are found in late summer or early fall when they are almost fully grown and are easy to see.

The caterpillars should be brought indoors, put in a terrarium or large jar and fed leaves from the tree or other plant on which they were found. Since these are usually almost fully grown caterpillars they finish feeding and pupate within a few days. The pupa is reddish brown and does not feed. Although showing little activity on the outside, large amounts of activity occur inside while the caterpillar structures are changed into butterfly or moth structures. Many pupae have protective cases of silk spun around them called cocoons.

The pupae are frequently the overwintering stages of the life cycle of these insects. Living in an area of the world with cold winters, these insects have a need for a lengthy time period of cold weather before they will continue to develop. Without a cold period, most overwintering pupae do not develop and die.

The pupae should be put into small screen cages or glass jars with holes punched in the lid. Bury these containers in fallen leaves or other debris under a bush or along the house and leave them there until April or May. In these containers, the pupae will be protected from mice, shrews and other small animals that may feed on them, but will be able to experience their needed cold period.

Although pupae placed in the refrigerator for 4 to 5 months will frequently develop into adults, better results are obtained with pupae that spend the winter outdoors. In the spring the pupae should be brought indoors and placed in a large screened cage or terrarium. This cage should contain a branch or other object that the new adult insect will be able to climb in order to dry its new body correctly. Within a few weeks, a butterfly or moth should emerge. Once it has had several hours to dry and rest, it should then be released outdoors.

Winter 1998
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