cocoon

A cocoon is a protective casing spun by the larvae of some insects, most notably many moth caterpillars, during metamorphosis from larva to pupa. The outer covering is typically made of silk produced by the larva's salivary glands, though some cocoons incorporate plant material or other substances.

In species that spin cocoons, the larva secretes silk and crafts a chamber around itself as it reorganizes into the adult. The pupa develops inside the cocoon, and the timing, shape, and texture of cocoons vary widely among species. Some cocoons are smooth and compact, while others are fibrous or layered and may be attached to vegetation.

Silk production is the best-known example of cocoon use. Domesticated silkmoths, particularly Bombyx mori, spin cocoons that are harvested for silk fibers. Before silk extraction, cocoons are often treated to soften the sericin that binds the silk filaments. In addition to sericulture, cocoons can serve ecological roles by providing protection from desiccation, predation, and parasitoids during pupation.

Not all Lepidoptera create cocoons. In many butterflies, the pupa is exposed and called a chrysalis rather than a cocoon. Similarly, some moths either abandon cocoon spinning or use alternative protective cases. The cocoon, therefore, is a specific strategy within a broader range of insect developmental adaptations.