usually a fibrous covering that protects the eggs or pupae of some arthropods

Cocos are created by, for example, some spiders, insects, millipedes or worms, usually from secretions of the silk glands that harden in the air. Either the adults deposit eggs and possibly nutrients (ootheca) in them, or the larva (e.g. caterpillar) makes them itself before pupating. In some species, the cocoon is formed by shedding and hardening the outer layer of the skin. Some caterpillars also attach small twigs, pellets or pieces of vegetation to the cocoon to hide it from predators. Others spin the cocoon in a protected or hidden place - under a leaf, in a crevice or at the base of a tree trunk. Natural cocoons are also formed by lemmings and lemmings.

Silkworm cocoons are processed into natural silk used to make fabrics.