Moulting

molting]] In biology, moulting or molting (both pronounced ), also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body (often but not always an outer layer or covering), either at specific times of year, or at specific points in its life-cycle.

Moulting can involve the epidermis (skin), pelage (hair, fur, wool), or other external layer. In some species, other body parts may be shed, for example, wings in some insects. Examples include old feathers in birds, old hairs in mammals (especially dogs and other canidae), old skin in reptiles, and the entire exoskeleton in arthropods.

Examples

Specific order notes

Birds

.]]

In birds, moulting is the periodic replacement of feathers by shedding old feathers while producing new ones. Feathers are dead structures at maturity, and they become gradually worn down and need to be replaced. Adult birds moult at least once a year, though many moult twice, and a few three times. Because feathers make up 4-12 percent of a bird's body weight, it takes a large amount of energy to replace them. For this reason, moults are frequently timed to occur right after the breeding season, but while food is still abundant. The plumage produced during this time is called postnuptial plumage. The same pet website page from which the following list was obtained clearly states "All dogs shed".

Reptiles

The most familiar example of moulting in reptiles is when snakes "shed their skin". This is usually achieved by the snake rubbing its head against a hard object, such as a rock (or between two rocks) or piece of wood, causing the already stretched skin to split. At this point, the snake continues to rub its skin on objects, causing the end nearest the head to peel back on itself, until the snake is able to crawl out of its skin, effectively turning the moulted skin inside-out. This is similar to how one might remove a sock from one's foot by grabbing the open end and pulling it over itself. The snake's skin is often left in one piece after the moulting process. Conversely, the skin of lizards generally falls off in pieces.

Amphibians

Both frogs and salamanders moult regularly and consume the skin, with some species moulting in pieces and others in one piece.

Arthropods

In arthropods, such as insects, arachnids and crustaceans, moulting is the shedding of the exoskeleton (which is often called its shell), typically to let the organism grow. This process is called ecdysis. Ecdysis is necessary because the exoskeleton is rigid and cannot grow like skin. The new exoskeleton is initially soft but hardens after the moulting of the old exoskeleton. The old exoskeleton is referred to as an "exuvia" (or exuvium).

Humans

While humans do not strictly molt, an important part of the skin's defense against fungi is stratum corneum turnover that removes the microbes by shedding the old skin surface. This is increased by the immune system detection of dermatophytes (skin living fungi) such as Trichophyton rubrum.

References

External links

Crayfish Moulting Video

Category:Developmental biology Category:Skin