Animals across the globe regularly renew their outer layers through a natural process called molting. This allows them to adapt, thrive, and maintain health in their environments.
Defining Molting
Molting is a widespread biological process where an animal sheds an outer layer of its body. This shedding can involve skin, feathers, fur, or an exoskeleton, and it is followed by the growth of new replacement material. It often occurs at specific times of the year or at various points in an animal’s development, ensuring its outer covering remains in optimal condition.
Reasons Animals Molt
Molting serves several purposes. Since many outer coverings, like an exoskeleton, cannot stretch, shedding allows the animal to increase in size. It also enables the repair of damaged or worn-out external parts, replacing them with fresh ones. Seasonal molting helps animals adapt to changing environmental conditions, such as growing a thicker coat for winter or a lighter one for summer. Shedding can also help animals eliminate parasites clinging to their outer layers.
How Different Animals Molt
Molting mechanisms vary across different animal groups.
Arthropods (Insects, Crustaceans, Spiders)
Arthropods, including insects, crustaceans, and spiders, undergo ecdysis to shed their rigid exoskeleton. Before shedding, a new, soft exoskeleton forms underneath the old one. The old exoskeleton then splits, often along the back, and the animal wriggles out, leaving behind the shed skin, known as an exuviae. The newly emerged arthropod is soft and vulnerable until its new exoskeleton expands and hardens over hours or days. This process also allows for the regeneration of lost limbs over a series of molts.
Reptiles (Snakes, Lizards)
Reptiles shed their skin periodically. Snakes typically shed their skin in one continuous piece, often turning it inside out as they crawl out. Lizards and turtles, however, usually shed their skin in multiple pieces or flakes. Before shedding, a reptile’s skin may appear dull, and the eyes of some species, like snakes, may become cloudy. They often rub against rough surfaces to help loosen and remove the old skin.
Birds
Birds replace their feathers through molting, ensuring their plumage remains functional for flight, insulation, and water repellency. This process is typically gradual, with feathers shed and replaced in a symmetrical pattern to avoid significant loss of flight ability. However, some birds, like penguins and ducks, undergo a “catastrophic molt” where they lose all their flight feathers at once, rendering them temporarily flightless. New feathers, initially appearing as “pin feathers,” emerge and push out the old ones.
Mammals
Mammals shed their fur or hair, which can be continuous or seasonal. Seasonal shedding allows mammals to exchange thick winter coats for lighter summer ones, or vice versa, to regulate body temperature and for camouflage. This process is influenced by changes in daylight and temperature, which affect hormone levels. While most mammals shed gradually, some, like elephant seals, undergo a more intense “catastrophic molt” where they shed large clumps of fur and skin simultaneously.
Life During Molting
Molting is an energetically demanding period for animals, requiring significant resources to produce new tissues. Animals may experience temporary physiological changes, such as hormonal fluctuations, which regulate the timing and progression of the molt. This process can also lead to increased metabolic rates as the body works to grow new outer layers.
During molting, animals often become more vulnerable to predators and environmental stresses. Arthropods, for example, have soft, pliable new exoskeletons immediately after shedding, making them susceptible to injury or predation until the new shell hardens. Birds undergoing a complete molt may lose the ability to fly, forcing them to seek secluded habitats. Reptiles may become irritable and less active during their shedding period.
Behavioral changes are common as animals adapt to their vulnerable state. Many species seek sheltered or hidden locations, reducing their activity levels. Some animals, such as penguins, may significantly increase their food intake before a catastrophic molt to build up fat reserves, as they cannot forage during shedding. Conversely, some birds, like chickens, may experience a temporary reduction in appetite during molting.