molt

Molt, also spelled moulting, is the process by which an animal sheds its outer covering and, in many cases, renews it. It is common in a wide range of taxa, including arthropods, reptiles, amphibians, birds, and some mammals, and occurs in different forms depending on the group.

In arthropods, molting is called ecdysis and is a key part of growth. The old exoskeleton is shed to permit a larger one to form. Hormonal controls involve ecdysone and juvenile hormone, coordinating stages that include loosening of the cuticle, shedding, and the hardening of a new exoskeleton.

In vertebrates, molts refer to the replacement of surfaces such as skin, hair, or feathers. Birds undergo seasonal or occasional feather molt, replacing old feathers with new ones to maintain flight and insulation. Mammals molt fur or hair regularly or seasonally. Amphibians and some reptiles shed skin in layers or during growth spurts, often in patches rather than as a single event.

Typical molt cycles include three phases: pre-molt (preparation, shedding of old tissues, color changes), molt (the shedding or replacement event), and post-molt (stretching or hardening of new tissue and pigment adjustments). Triggers include hormonal signals, photoperiod, temperature, nutrition, and environmental conditions.

Functions of molting include growth, renewal of protective coverings, repair from wear or parasite load, and adjustments in camouflage or insulation. Abnormal molting can indicate health problems, such as nutritional deficiency, injury, or disease, and some species exhibit incomplete molts or retained shed.

See also: ecdysis, feather molt, hair molt.