Walking by one of the wonderful old New England stone walls or hedgerows, one might find an impressive cast-off skin of a large black racer, Coluber constrictor. These snakes can be longer than a person is tall, and an unexpected meeting gives almost almost everyone an adrenaline rush.
Shed Skins Are Everywhere – Just Look For Them
When insects, spiders, crabs, and snakes grow, they molt their outer coverings after making new ones beneath. The shed coverings (exoskeletons) of crabs and horseshoe crabs, Limulus polyphemus, (more closely related to spiders than to crabs) often decorate our beaches. The shed exoskeletons (exuviae) of dragonflies and damselflies (Odonates) can be found along the banks of ponds and rivers. Exuviae of caterpillars, butterfly chrysalids, and moth pupae (Lepidopterans) are on trees and shrubs. Stone walls and bushes often support shed snake skins.
Looking at the soft bodies of dragonfly larvae, caterpillars, and snakes, one might assume their skin would grow with them. But that is not the case. Their exoskeletons are pliable, but not elastic. They can bend, but cannot stretch to allow growth. Although not exoskeletons, scales in the skins of snakes are also not elastic and cannot stretch.
Functions Of Molting
Molting is under hormonal control. While preparing to molt, animals absorb many of the molecules in their scales and skins while producing the new skin developing below the thinning old ones. When the time comes to molt, the old skin splits and the animal crawls out of it, gulps air (or water in the case of marine animals), and stretches the pliable new skin until it hardens.
Although crustaceans and snakes continue to grow and molt their entire lives, the number of molts is constant for each insect species. The first four or five molts produce larger larvae, but the last one or two involve dramatic changes in form, activity, and function called metamorphosis.
Depending on weather conditions, caterpillars of the black swallowtail, Papilio polyxenes, can double their size in two or three days of eating. These caterpillars can metamorphose to a chrysalis in less than a month. Some of the larger moth caterpillars may take two months to do the same thing, and large dragonflies may take two summers to reach adulthood.
People who study monarch butterfly, Danaius plexippus, migration often find small butterflies with saturated, brown coloration instead of the brilliant orange colors of the normal sized butterflies. These smaller monarchs hatch out of eggs laid too late in the season to pass through all five larval stages. The shortening day length of autumn forces fourth stage caterpillars to metamorphosis prematurely, producing smaller butterflies, but the alternative is possibly freezing to death.
Unlike insects, crustaceans and snakes continue to grow as long as they live, and the frequency of molting is determined by the speed at which they grow. Note: Rattlesnakes, Crotalis spp., produce a new button at the end of their rattles each time they molt. Thus, the number of "buttons" in a rattlesnake's rattle indicates the number of times the snake has shed its skin, but does not indicate the actual age of the rattlesnake. Since the buttons are rather brittle, they sometimes break off and reduce the count.
What is Molted
Every structure derived from the outer surface of the insect embryo is covered with exoskeleton, and every one of these tissues sheds. If you look closely at the shed skin of an insect, you will find it is composed of the surface of the eyes, leg and wing coverings, all hairs, and even many structures found inside the animal's body: the lining of the mouth, lower intestine, and the tiny tubes (called tracheae) through which the animal breathes. The same is true for horseshoe crabs and dragonfly larvae (where the external gill surfaces are also molted).
Snake sheds have a slightly different composition. Snakes do not shed linings of internal structures, but since transparent scales cover their eyes, snakes shed these eye covers. Thus, although found in an insect exuvia, the lining of the mouth, lower intestine, and respiratory tract are not included in a shed snake skin.
The manners in which animals exit their skins also differ. Crab (Carcina spp.) sheds split at the base of the tail, while horseshoe crab sheds are split at the leading edge of the head region. Insect sheds split down the back and head. Snakes simply crawl out of their old skins from head to tail (much like pulling an undershirt over the head), pulling against hard surfaces. Thus, snake skin sheds are inside out while shed insect and crab exoskeletons have normal orientation.
Pet Snakes And Lizards Need Help Shedding
Rocks and branches in the cage of a pet snake or lizard are essential to help it shed. These animals need a source of friction to pull their skins over their heads (snakes) or rub them off (lizards). Snakes reduce their food requirements before shedding and live prey should not be provided for them when their eye scales become bluish (indicating the molt will occur soon).
Be Wary Of Pre-molting Snakes In The Wild
One should always be careful when handling snakes, but more so as they prepare to molt. As the scales over their eyes lift off the surface, their vision is clouded. In addition, the skin appears to become quite itchy and irritating, giving them a peevish temperament. Some snake species, like the nonvenomous northern water snake, Nerodia spideon, bite whenever they have the chance, sometimes before being caught. When about to molt, a corn snake, Elaphe guttata,a normally gentle species, will demonstrate a disposition almost as unpleasant as that of a water snake: lunging and striking at a person - even one attempting to help it across a busy street or about to feed it.
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