All reptiles shed their skin, a biological necessity known as ecdysis, but the method varies significantly across major groups. While the underlying purpose is shared among all snakes, lizards, turtles, and crocodiles, the physical act of shedding is highly specialized for each animal’s unique body structure and environment. This variation means that a snake’s complete skin shed is a different process entirely from the continuous, gradual scale replacement seen in a crocodilian.
The Biological Necessity of Skin Shedding
Skin shedding is necessary for a reptile because its outer layer, the epidermis, is inflexible and cannot stretch to accommodate growth. As a reptile increases in size, the old layer must be replaced by a larger, newer one beneath it, a requirement that makes shedding much more frequent in young, rapidly growing individuals. This replacement process is also the primary mechanism for repairing accumulated damage, such as minor wounds or scrapes, and maintaining the skin’s protective integrity.
Before the actual shed, a specialized layer called the stratum intermedium forms between the old outer skin and the new skin underneath. This new layer secretes a lymphatic fluid rich in enzymes, which acts to dissolve the connections between the old and new skin layers. The infiltration of this fluid allows the dead outer layer, known as the stratum corneum, to separate and loosen from the body.
The periodic removal of the entire outer epidermis also serves a hygienic function. Shedding effectively removes external parasites, such as mites, which may have attached to the skin’s surface. It also helps to eliminate waste products, dirt, or accumulated bacteria that have bonded with the keratinized outer layer.
Diverse Methods of Ecdysis Across Reptile Groups
The physical mechanics of ecdysis differ substantially depending on whether the reptile belongs to the Squamata (lizards and snakes) or a different clade like the Chelonians (turtles) or Crocodylia (crocodiles and alligators).
Snakes
Snakes are the most widely recognized shedders because they typically perform a complete, single-piece ecdysis. Before shedding, a snake enters a preparatory stage often called “in the blue,” where the fluid separating the skin layers causes the clear scale covering its eye, the spectacle, to turn opaque. Once the separation is complete, the snake uses rough surfaces in its environment, such as rocks or bark, to rub the old skin loose, typically starting at the snout. The skin then peels back over the body, resulting in a single, perfectly preserved skin casing. The inclusion of the spectacle in this single piece is a sign of a successful shed.
Lizards
Lizards, in contrast to snakes, perform a fragmented or patchy shed, with the old skin coming off in multiple pieces or strips. They commonly use their mouths to pull and peel the dead skin from their bodies, often consuming the shed skin in a behavior known as dermatophagy. This behavior is thought to recover valuable nutrients and proteins. The patchy nature of a lizard’s shed means that retained skin is a common concern, especially around the extremities, such as the tail tip and toes.
Turtles and Crocodilians
Chelonians and crocodilians utilize a continuous process of scale replacement called desquamation rather than a dramatic, full-body shed. They gradually replace individual scales or scutes over time. Turtles and tortoises shed the thin skin on their necks and limbs in small flakes, while the scutes covering their bony shell are also shed individually. Crocodilians also replace their scales continuously, which is necessary because their skin is reinforced with bony plates called osteoderms beneath the surface.
Understanding Dysecdysis
Dysecdysis is the term for any abnormal or incomplete shedding process, and it is a common indicator of underlying health or husbandry issues in captive reptiles. The most frequent environmental cause is low humidity, which prevents the proper hydration of the old skin layer, inhibiting the action of the separating enzymes and causing the skin to stick. Suboptimal temperatures and a lack of abrasive surfaces can also contribute to a failed shed, as the reptile cannot physically rub the loosened skin off.
Nutritional deficiencies, particularly an insufficient intake of Vitamin A, can severely impair the production of healthy new skin cells, leading to dysecdysis. Internal factors like chronic illness, internal parasites, or hormonal imbalances also negatively affect the shedding cycle. Dysecdysis is not a disease itself but a symptom that requires correction of the primary cause.
The consequences of a failed shed can be severe. In snakes, retained spectacles can lead to blindness or corneal damage if they accumulate over multiple sheds. Retained skin on the limbs or tail of lizards can dry, harden, and constrict blood flow, acting like a tight band that can cause tissue necrosis or the loss of digits. If the retained skin is not removed, the resulting irritation and compromised barrier function can quickly lead to secondary bacterial or fungal infections.