spontaneous interruption of the development of certain animals, marked by reduction of metabolic activity. It is typical of many insects and mites, a few crustaceans and snails, and perhaps certain other animal groups. This period of suspended development is an apparent response to the approach of adverse environmental conditions. It may occur during any life stage but is most common among pupae (e.g., the cocoons of moths).

Diapause sets in when the bodily concentrations of growth and molting hormones decrease, which usually coincides with changes in day length, temperature, or abundance of food. Diapause is genetically determined but may be eliminated experimentally if the animals are raised under constant and favourable environmental conditions.