GROWTH AND SHEDDING. A snake’s skin is...
... periodically shed, often in a single piece (or nearly so). The process is called ecdysis. Actually, they shed only the outer layer of the epidermis; see various publications by Brian Gray for fabulous explanations of the process (see here and there).
Exposed to the weather, shed skins can become brittle, be shredded by birds or other animals, or simply decay by the activities of fungi, bacteria, and insects. Interestingly, it is well known that Crested Flycatchers use shed skins in their cavity nests. I wonder if the light colored shed is still visible enough to potentially deter nest predators?
Snake scales come in two versions—one with a ridge down the center (Keeled scales) and those without a ridge (Smooth scales). Many researchers have investigated the function of these ridges. They may help snakes climb, swim, or collect water (for drinking off their coils). Most fossorial snakes have smooth scales. Eight of our Western Mass species have keeled scales, while five are smooth. Ratsnakes are a bit unusual: some of their side body scales are smooth, but a varying number of rows on either side of the midline have ridges. Go figure.
Most shed skins show the patterns, or lack thereof, that the snake’s body had in life. You can see this best by holding the skin up to the light. Also you will note that there is a scale where the eye was. This is a specialized scale (called a brille or spectacle) that protects the eye in lieu of eyelids.
There are many studies on the microscopic structure of snake scales that illuminate a complex picture of snake morphology; the results may lead to a better understanding of how snakes perceive the world (tactile interactions, pheromone production) and more about snake lives. For instance, are there differences between ages and sexes?
How often does a snake shed its skin? The short answer is, “it depends.” Some of the confounding factors include age, sex, reproductive condition, food (nutrition), disease, injury, seasonal weather, and a bunch of other things we don’t understand. With more researchers following wild snakes with radio-telemetry, this question can be studied in much more detail. Snakes, and a few other animals, grow continually throughout their lives (called indeterminate growth) though growth after maturity is relatively small. It is possible that some small snake species have determinate growth where they no longer grow after becoming sexually mature.
Another Reference: Andrew Durso has a great web site on shed snake skins of the Northwestern US and a lot of other interesting stuff you might enjoy.
Right: If you want to pick up a shed skin, do look carefully to make sure the snake is not still there!