Molt

Definition

The process of shedding and replacing the exoskeleton (cuticle) or other external body covering during growth or metamorphosis. In arthropods, molting is hormonally regulated and involves the secretion of a new cuticle beneath the old one, followed by ecdysis (the actual shedding), expansion of the new cuticle, and sclerotization. The interval between molts is termed an instar.

Etymology

Middle English mouten, from Latin mutare 'to change'

Example

A fifth-instar caterpillar molts to become a pupa; a tarantula may molt 4–6 times per year during its growth phase, becoming temporarily soft-bodied and vulnerable until the new exoskeleton hardens.

Synonyms

• Ecdysis
• moult
• sloughing

Related Terms

• instar
• Ecdysis
• Ecdysone
• Cuticle
• exuvia
• apolysis
• Sclerotization
• ecdysteroid

Usage Notes

Specialists distinguish 'molt' (the overall process including preparation and recovery) from 'ecdysis' (the act of shedding itself). 'Sloughing' is more common in vertebrate contexts (snakes, amphibians). The British spelling 'moult' is equivalent. The discarded exoskeleton is properly called an exuvia (plural exuviae), not 'a molt'.