Molting in Birds, Snakes, Krill and More

Some animals’ bodies grow but their skin does not. To continue to develop, the animal must shed the old skin and grow a new one. This process is known as moulting, or molting. Molting and shedding are very similar except that shedding is often done in the interest of climate changes throughout the seasons of the year. Nearly all types of animals molt or shed in some manner.


Dogs don’t molt, they shed. However, it is the same basic concept. Dogs shed twice each year, once in the springtime and again in the fall. Most people understand the spring shedding because the dog is ridding itself of extra hair it doesn’t need to be burdened with through the hot summer. However, a lot of people are confused about why dogs shed in the fall too. Don’t they need the hair to keep warm during the winter? Yes, they do. Dogs shed in the fall to make room for a thicker coat of fur that will grow in. A dog’s shedding can be affected by breed, pregnancy and how much time it spends outside.


Birds do not have fur like dogs. Instead, they molt feathers. Feathers are “dead” just like human fingernails. They do not change in color. Yet birds change color sometimes, especially with different seasons. This is because they lost their old feathers and grew new ones. Some birds including ducks, swans and pelicans, molt all of their feathers at the same time and remain vulnerable during a two week period when they can’t fly. This is known as a complete molt. Other birds undergo a partial molt where the feathers are replaced gradually. Birds also molt because their feathers will wear out no matter how often they take care of them. Young birds also lose their soft, down feathers and molt new adult plumages. In some breeds this takes several years.


Reptiles shed their skin in just one day. The most well-known shedding process for reptiles is that of the snake. Snakes climb out, usually through the mouth hole of their old skin. To assist with the process, they wet their bodies and sometimes rub against twigs or stones to catch the old skin and hold it in place while they wrestle their way out. The cast skin is left over in one piece afterward. Snakes and other reptiles molt two to five times each year.


Like reptiles, amphibians replace their entire skin at once. They do so at least once each season (every three months or so). Frogs stretch out their bodies by hunching and scrunching so that the old skin comes off more easily. Unlike a snake, however, frogs, toads and other amphibians eat the skin cast.


Arthropods (crabs, lobsters, krill and insects) molt very differently from other types of animals. They grow an exoskeleton, which is like having bones on the outside of their body. This exoskeleton is very strong like a shell. These exoskeletons give their boneless bodies shape and protection.

When they are ready to molt, arthropods split through the exoskeleton. Insects, which comprise about 90% of arthropod species, typically molt six times throughout their lives. The time spent between molts is time the insect spends without an exoskeleton. This is when they are at their most vulnerable and also when most of them die. A familiar example is the metamorphosis of a caterpillar to a butterfly. The cocoon is actually a form of molt. Like amphibians and reptiles, the molt stays in one piece. Scientists used to have trouble determining whether a trilobite (ancient sea-dwelling arthropod) fossil was an animal or just the molt.


Human beings do not “molt” like other animals. However, we do shed our skin constantly. Skin cells die often and we shed millions of them every day. Part of this process is skin regeneration. Most of the body’s cells multiply, so skin cells are being produced as quickly as others die. If skin cells begin dying faster for one reason or another, the body produces new skin cells faster to maintain a certain thickness of skin.