Snakes shed periodically, and if the conditions are right the entire skin normally comes off in one piece, a procedure that can be likened to removing a sock. Snakes replace their skins to allow for growth, as well as to remove parasites along with the old skin.
Here a snake shed from a juvenile red-necked keelback, with some fancy lighting.
I have also noticed that the shed allows for the snakes to repair damaged skin, and heal wounds.
When the old skin is shed, it doesn’t look exactly the same as its replacement. The skin takes on a nearly transparent appearance, and, due to stretching, is larger than the snake. You can, or at least experts can, sometimes use the skin to identify what the snake was.
Ecdysis is the scientific term for shedding the skin, and other animals that shed their skin include a variety of insects, arthropods and lizards. This process is also commonly referred to sloughing or molting the skin. With snakes, however, the word "shedding" is used most often.
Here some more shots of the shed, greatly enlarged, showing the individual scales.
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