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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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Update: June 2012
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