How does moulting occur in reptiles?

The reptile’s integument plays particularly important roles: it protects it from external aggression, abrasion, dehydration and UV rays, plays a role in social behaviour, allows the synthesis of vitamin D…. Moulting is part of the regeneration process of this integument. During moulting, the reptile renews its superficial part: the epidermis.

The different types of moulting

Moulting takes place in different ways depending on the reptile species. Lizards shed their old skin in large patches that they can eventually eat to benefit from the amino acids they contain. Ophidians (snakes) shed their skin all at once, while chelonians (turtles) shed their skin very discreetly, losing small flaps intermittently.

The moulting process

The epidermis of reptiles consists of three layers of keratin (a highly resistant protein) secreted by the germinative layer. The outermost keratin layer (α-keratin) is also the thinnest and most resistant, while the innermost (α-keratin) is very elastic, allowing movement. Before moulting, the reptile synthesizes new layers of keratin underneath the old ones. Then, enzymes are secreted which will come to take off the old “skin” (also called “exuviate”) from the new one. This entire preparation process takes about two weeks in snakes and lizards.

During this time, the snakes are calmer, their color becomes dull and their skin opaque. This opacity also affects the transparent scales that cover their eyes, which impede their vision. It is then easily understood that the snake, almost blind, has a slightly modified behavior (aggressiveness, apathy …). During this period, it is advisable to avoid handling your snake, because it could cause small tears in the exuvia, fragment it, and prevent the snake from moulting normally, that is to say in one go. Then comes the moment when the snake actually gets rid of the old layers of its epidermis, which only takes a few minutes to a few hours maximum. Immediately afterwards, the skin is shiny and the colors are vivid.

Caution: During the moult, the permeability of the skin is increased. Therefore, any pest control treatment should be avoided during this period.

How often does the skin moult?

Moulting disorders are easily noticeable in snakes (e.g. when snakes do not moult all at once). On the other hand, they are sometimes difficult to detect in lizards, which moult in fragments. There are different moulting disorders.

1) Dysecdysis

In most cases the moult is blocked. This is called “dysecdysia”. This problem is quite common in lizards and snakes, rarer in turtles.

Dysecdysis manifests itself by a persistence of exuvia on the reptile (dry, opaque, wrinkled skin) or by a persistence of the “pre-corneal glasses”, i.e. the transparent membrane that covers the cornea, which is supposed to leave with the rest of the exuvia. This can cause dermatitis, itching and conjunctivitis. But it can also be more serious, especially if the exuvia flaps persist on extremities such as the fingers or the base of the tail; they can then impede blood circulation, cause dry gangrene and lead to amputation. Prompt intervention is therefore necessary.

Abundant sprays of warm water or a bath at 30°C under supervision for one or two hours, followed by gentle removal of the flaps with forceps, can then help the reptile get rid of the persistent exuvia. Regularly check the temperature of the bath water, which can drop rapidly, especially if the container is shallow. You can also wrap it in a warm damp towel. 1] In lizards, remember to check that there are no pieces of exuviate left on the fingers. If not, you can remove them after a bath, by rubbing them with a wet cotton bud for example.

It is preferable not to touch the pre-corneal glasses, because of the risk of corneal damage if you pull on the scales when they are not quite ready to come off. Just irrigate them, and ask your veterinarian for advice if they still persist.

The causes of dysecdysia vary widely. Most often, it is related to a poor general condition, or to unsuitable maintenance conditions.

-environmental causes

The first is insufficient hygrometry in the terrarium, which leads to dehydration of the exuvia and then of the reptile itself. Insufficient temperature can also lead to such disorders. It is imperative to equip your terrarium with a hygrometer and a thermometer and to check these parameters daily. If the hygrometry is too low, place a bowl of water in the terrarium under the heating lamp. It is possible to slightly increase the hygrometry of your terrarium before moulting, as a preventive measure. Finally, the exuviate can persist if the reptile does not have rough surfaces in the terrarium to rub (rocks, stones), because snakes begin their moult by rubbing against a rough object to remove an edge of the exuviate at the lips, then they turn it over like a glove finger.

Once the environmental parameters have been reviewed, if the problem persists, a medical cause must be considered.

-medical causes

Skin problems (dermatitis) caused by bacteria or fungi can hinder moulting just like dust mites. These are very common in reptiles, both in the wild and in captivity. In ophidians they are mainly Ophyonyssus natricis, a very mobile red and black parasite, about 1 mm long [2]. 2] It can be eliminated by applying antiparasitic products between moults. Ask your veterinarian for advice.

Burns or scars can also form areas of adhesion and retain the exuviate.

Finally, a lack of protein or vitamins (especially vitamin A) due to malnutrition or an unsuitable diet promotes dysecdysia, because the reptile does not have the energy to moult properly.

2) Excessive moulting

More rarely, the problem concerns excessive moulting. In this case the molts are extremely close together, every 15 days for example for a snake. It happens then that the snake stops feeding. The moult is controlled by thyroid hormones. The absence of a nycthemeral rhythm (variations in light and temperature simulating day/night alternation) can favour the appearance of hyperthyroidism. Excessive moulting is then observed in snakes, with persistence of the corneal bezel.

The prognosis is then rather gloomy. There is no really effective treatment, the only thing to do is to restore a cyclic variation of brightness and temperature.

The other causes of excessive moulting are environmental: excessive temperature and humidity.