Eclosion

A pupa (Latin pupa for doll, plural: pupae or pupas) is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages: embryo, larva, pupa and imago.

The pupae of different groups of insects have different names such as chrysalis for the pupae of butterflies and tumbler for those of the mosquito family. Pupae may further be enclosed in other structures such as cocoons, nests or shells.

In the life of an insect the pupal stage follows the larval stage and precedes adulthood (imago). It is during the time of pupation that the adult structures of the insect are formed while the larval structures are broken down. The adult structures, imaginal discs, then grow to become the adult structures. Pupae are inactive, and usually sessile (not able to move about). However, the pupae may be exarate (have movable legs, wings, antennae, etc.) or obtect (covered in a hard case with the legs and wings attached immovably against the body). They have a hard protective coating and often use camouflage to evade potential predators.

Pupation may last weeks, months or even years. For example, it is two weeks in monarch butterflies. The pupa may enter dormancy or diapause until the appropriate season for the adult insect. In temperate climates pupae usually stay dormant during winter, while in the tropics pupae usually do so during the dry season. Anise swallowtails sometimes emerge after years as a chrysalis.

...
Wikipedia