Ecdysis

Definition

The process by which arthropods and other ecdysozoans shed their exoskeleton (cuticle) to permit growth, involving enzymatic separation of the old cuticle from the epidermis, emergence through a predetermined split, and expansion and sclerotization of the new cuticle beneath.

Etymology

Greek ecdysis, 'to strip off' or 'get out of'

Example

A fifth-instar caterpillar initiates ecdysis by secreting molting fluid beneath its old cuticle, then contracts to split the head capsule and crawls backward out of the shed skin, remaining motionless while the new, larger cuticle expands and hardens over several hours.

Synonyms

• molting
• moulting

Related Terms

• exuvia
• Exuviae
• instar
• Teneral
• ecdysteroid
• apolysis
• ecdysis-triggering hormone
• Cuticle
• Chitin

Usage Notes

Ecdysis is the specific physiological event of shedding; the broader preparation phase including cuticle loosening is apolysis. The term applies to all Ecdysozoa (arthropods, nematodes, tardigrades, etc.) but is most commonly used in entomology and arachnology. Post-ecdysis individuals are termed teneral until the new cuticle fully hardens. The discarded remains are exuviae (singular exuvium or exuvia).