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Molting in Reptiles and Amphibians
Nature Bulletin No. 642-A   May 21, 1977
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

MOLTING IN REPTILES AND AMPHIBIANS
A snake or a frog sheds its whole skin in one piece in just one day. On the contrary we lose a little of ours every day. Some is worn away and some is soaked loose every time we bathe. We do not realize how fast our skin grows until we have a broken arm or leg and see the crust of dead skin that forms under the case where it cannot be washed or scratched.

Hair and feathers are really parts of the skin of mammals and birds. Dogs -- at least house dogs -- shed hair the year round. In contrast, a fur-bearing animal such as a mink loses its thick underfur in spring and grows a new coat before the next winter. Wild birds, as a rule, molt their feathers and replace them a few at a time so that they are always able to fly. Wild ducks and geese, on the other hand, lose all of their night feathers soon after nesting. Then, for a few weeks, while a new set of feathers is growing, they cannot fly. In order to grow, young insects, spiders and crayfish must exchange their tough outer coverings for new and larger ones.

For several days before a snake molts the eyes appear bluish or cloudy, the pupil cannot be seen, and they are said to be blind. This is because of air under the outer coverings of the eyes which are shed as part of the skin. Luring this period snakes do not eat but hide away as if they felt insecure. Molting is hastened by wetting. The skin around the lips loosens first and is slowly forced back over the head, neck and body, inside out, as the snake crawls over rough surfaces and through narrow crevices. The snake now is shiny, the colors bright, and the eyes clear. The adults of our common kinds molt two to five times a year -- the young ones oftener because they are growing faster.

The cast skin is a horny substance much like our fingernails and almost transparent. Because of the folds or "tucks" under the edges of the overlapping scales, the straightened skin is about a third longer than the snake it came from.

Rattlesnakes shed like other snakes except that a part of the skin on the tail is not cast off but is elaborately modified and added to the horn-like string of rattles. Thus, the number of rattles represents the number of molts and not years of age as is popularly supposed. Furthermore, rattles break off so commonly that they do not show the number of molts unless the "button" representing the first molt is still on the tip.

Lizards usually shed their skins in scraps, often starting by a split down the back. The glass snake, actually a legless lizard rarely found in this region, molts in one piece as snakes do, except that the skin is not turned inside out.

All turtles, with the exception of the soft-shelled species, are enclosed in a bony shell which is covered with horny shields. In the common painted turtle the outer layer of these shields is shed, leaving the vivid colors of the shell fresh and bright. In the snapper, and perhaps most turtles, new and larger layers seem to be added to the underside of these shields each year as the shell grows. Thus rings are formed which can be counted to determine age, at least during early life.

The amphibians -- frogs, toads, salamanders and their kin -- have thin skins which they regularly shed in one piece and then eat them. This happens between once a week and once a month. The molting of a toad is a laughable sight not often seen because it happens so quickly. With the head down and the back humped, the skin splits down the back and belly, then crosswise. By puffing up the body the skin works forward and the legs are freed by rubbing against the body. Then the eyeballs pump in and out as the skin is swallowed in a black lump.

The molting snake got too big for his britches.


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