Preecdysis

Preecdysis, also written as pre-ecdysis, is a preparatory phase in the molting cycle of many arthropods, particularly insects, that occurs after apolysis and before the actual shedding of the old exoskeleton (ecdysis). During this stage the old cuticle is loosened from the underlying epidermis and the organism begins physiological and behavioral preparations for molt.

In preecdysis, the epidermal layer remains separated from the old cuticle (apolysis continues) and processes such as molting fluid activity and cuticle softening begin or intensify. The phase is coordinated by neurohormonal signals, and it often includes early, less forceful motor patterns that gradually prepare the body for the next, more vigorous shedding movements. These preparatory contractions help loosen the old exoskeleton and can influence body shape and internal pressure in anticipation of ecdysis.

The duration and characteristics of preecdysis vary among species and molts. In many insects, this phase is followed by the ecdysis itself, during which the insect actively sheds the old cuticle. While preecdysis is widely recognized in insect physiology, its exact mechanisms and timing can differ, and some literature emphasizes its role as a distinct preparatory window within the broader molt sequence.