Molting, or sloughing, is a natural process where animals shed their outer layers. This biological event involves casting off old skin, exoskeletons, or feathers to facilitate growth, repair, or adaptation. While mechanisms differ, shedding is a common part of the life cycle for many creatures, from tiny insects to larger reptiles. It allows organisms to renew and maintain their external coverings.
Why Animals Shed Their Skin
Animals shed their outer coverings for biological reasons, primarily linked to growth and maintaining protective layers. For many invertebrates, especially arthropods like insects, spiders, and crustaceans, their rigid external skeleton (exoskeleton) does not grow with them. This inflexible outer shell provides protection and support, but restricts continuous growth. Periodically, they must shed their old exoskeleton and grow a new, larger one to expand their bodies and progress through life stages. Beyond growth, shedding also replaces damaged or worn-out layers, ensuring continued protection and functionality.
The Process of Shedding
The process of shedding, particularly in arthropods, is called ecdysis. Hormonal signals, such as ecdysone, initiate this process. First, the old exoskeleton separates from underlying epidermal cells, a stage known as apolysis. A molting fluid containing inactive enzymes is then secreted between the old and new layers.
As the new cuticle forms, these enzymes become active, digesting the inner layers of the old exoskeleton. This allows the animal to reabsorb materials from the old cuticle, conserving resources. Once the new outer layer is developed and the old one is weakened, the animal typically swells its body by taking in air or water. This causes the old exoskeleton to split along predetermined lines of weakness. The animal then wriggles out of its old skin, leaving behind the shed remnant, often called an exuvia.
Animals Known for Shedding Their Skin
Many creatures shed their outer layers, especially invertebrates with exoskeletons. Insects like cicadas, grasshoppers, and caterpillars molt multiple times throughout their larval and nymph stages to grow. Spiders and scorpions, which are arachnids, also shed their rigid exoskeletons to increase in size, often retreating to a safe place during this vulnerable period. Crustaceans like crabs and lobsters similarly undergo ecdysis, shedding their hard shells to accommodate growth.
Many reptiles also shed their skin. Snakes typically shed their entire outer layer in one piece, often by rubbing against rough surfaces. Lizards, including geckos and iguanas, usually shed their skin in patches, though some species may shed in a single piece. Amphibians like frogs also shed their skin regularly, sometimes consuming it afterward.
Life After Shedding
Immediately after shedding, many animals enter a period of heightened vulnerability. The new outer layer, whether exoskeleton or skin, is typically soft and pliable, offering less protection against predators and environmental hazards. For arthropods, the newly emerged animal is often described as “teneral,” appearing pale and soft-bodied.
Over hours to days, the new covering hardens and darkens through sclerotization or tanning. Many animals expand their bodies before this hardening occurs, allowing for subsequent growth. Some animals, like certain lizards, geckos, and amphibians, consume their shed skin. This behavior helps them reclaim valuable nutrients and minerals and eliminates evidence that could alert predators.