Molting is a biological process where an animal sheds an outer layer of its body, such as skin, fur, feathers, or an exoskeleton. This natural, recurring event allows many species to renew and adapt their external coverings, supporting their growth and survival.
Why Animals Molt
Animals molt for a variety of important biological reasons. One primary reason is growth; many animals possess rigid outer coverings that do not expand as their bodies increase in size. By shedding this restrictive layer, they can grow larger and form a new, more accommodating external structure.
Molting also serves to repair and replace worn or damaged body parts. Feathers, fur, or skin can become frayed, broken, or infected, and shedding these old layers allows for new, healthy replacements. This renewal maintains the integrity and function of these crucial coverings. Molting also enables seasonal adaptation, such such as changing fur color for camouflage or growing denser coats for insulation. It can also help remove external parasites.
Who Molts and What They Shed
Molting occurs across a wide range of animal groups, each shedding different external structures. Invertebrates like insects, spiders, and crustaceans undergo ecdysis, shedding their rigid exoskeletons. Since this hard outer shell does not grow, shedding it is essential for the animal to increase in size. For example, a lobster sheds its exoskeleton to grow, and a new, larger one hardens over time.
Reptiles and amphibians regularly shed their skin. Snakes often shed their entire skin in one piece, while lizards might shed in patches. Amphibians like frogs also periodically shed their skin, with some even consuming the shed layer.
Birds molt their feathers to replace old, worn plumage important for flight, insulation, and display. This can be a partial or complete molt.
Mammals undergo seasonal shedding of fur or hair, typically to adapt to temperature changes or remove old hair. This process is continuous in some mammals, while others experience more pronounced seasonal events.
How Molting Happens
Molting is controlled by internal physiological mechanisms, primarily hormones. In insects, hormones like ecdysone trigger the shedding process. Before the old outer layer is shed, a new one begins to form underneath it. This new layer develops beneath the existing one, providing a protective covering once the old one is cast off.
As the new layer forms, the old outer covering loosens and separates from the animal’s body. The animal then removes the old layer, which can involve muscular contractions, rubbing against objects, or inflating its body with air or water to split the old covering. After shedding, the newly exposed layer is often soft and vulnerable, requiring time to harden or mature. This hardening ensures the new outer layer provides proper protection and function.
The Vulnerability and Resilience of Molting Animals
Molting is an energetically demanding process that leaves animals vulnerable. During and immediately after shedding, an animal’s new outer layer may be soft, thin, or incomplete, offering reduced protection from predators and environmental hazards. For example, crustaceans are soft-bodied after shedding their exoskeleton, and birds may temporarily lose flight capabilities during a complete molt. The energy expended during molting can also make animals more susceptible to temperature fluctuations and require additional food resources.
Despite these risks, animals have developed coping mechanisms and adaptations to ensure their survival during this period. Many seek secluded or sheltered locations to hide from predators, such as burrows or dense vegetation. Some species reduce their activity levels to conserve energy and minimize exposure. Certain animals, like some crustaceans and amphibians, may even consume their shed outer layer to reabsorb valuable nutrients and calcium. The new layer typically hardens or matures quickly, allowing the animal to regain full protective capabilities and resume normal activities.