ecdysises

Ecdysis is the process by which ecdysozoan animals, most notably arthropods such as insects, arachnids, and crustaceans, shed their outer exoskeleton or cuticle. This shedding, or molting, enables growth beyond the size that the current cuticle allows and is a central feature of their development and metamorphosis. The shed skin is called an exuvia.

The word ecdysis derives from the Greek ekdysis, meaning shedding or unfolding. Ecdysis is a recurring developmental event, repeated several times during the life cycle of most arthropods. It is tightly integrated with hormonal control and timing, ensuring that growth occurs in discrete steps rather than continuously.

In insects, molting is governed by an endocrine cascade. The brain secretes prothoracicotropic hormone (PTTH), which stimulates the prothoracic glands to produce ecdysone. The active form, 20-hydroxyecdysone (20E), triggers the molting program. The level of juvenile hormone (JH) determines the outcome of a molt: when JH is high, molts typically produce another larval instar; when JH falls, the molt can yield pupation or adult development. The physical sequence of ecdysis involves ecdysis-triggering hormone (ETH) and eclosion hormone coordinating the behavioral steps, while the old cuticle is shed and a new, expanded cuticle expands and hardens.

The molting process consists of premolt (apolysis, separation of epidermis from the old cuticle), ecdysis (successful shedding), and postecdysis (expansion and hardening of the new cuticle). Ecdysis is essential for growth and development, and its timing is influenced by environmental factors such as temperature and nutrition.

Exuviae (shed skins) are often used in scientific study and paleontological reconstruction. In applied contexts, molting disruption is a target in some pest-management strategies.