eclosion

Eclosion is the emergence of an insect from a previously enclosed life stage, most commonly the process by which an adult insect emerges from a pupal case or chrysalis at the end of metamorphosis. The term is also sometimes used to describe the hatching of an insect from an egg, depending on the group and the source. In moths, butterflies, beetles, and other holometabolous insects, eclosion begins when enzymes soften and rupture the outer pupal wall or exuvia and the adult pushes free of the casing. After emergence, the insect typically pumps hemolymph into wings and other structures to inflate and dry them, and it undergoes cuticle hardening (sclerotization). The empty pupal case, or exuvia, may remain attached to substrate or be shed as the insect frees itself.

Timing and synchrony of eclosion are influenced by environmental conditions such as temperature, humidity, photoperiod, and nutrition during larval and pupal development. In many species, eclosion is tightly timed to seasonal cues or food availability, sometimes producing mass emergences. Because eclosion marks the transition to reproductive maturity in many species, it is often used as a developmental marker in research and insect-rearing programs.

Eclosion differs from basic ecdysis, which is the shedding of the old cuticle during molts within larval or nymphal stages; eclosion specifically refers to the final emergence of an adult from a pupal case or egg capsule.