Snakes range from 4 inches (10 cm) to more than 30 feet (9 meters) in length. Hundreds of tiny vertebrae and ribs span this distance and connect to each other through an intricate system of muscles, creating unrivaled flexibility (See Getting Around section). An extremely elastic skin attaches to the muscles and is covered with scales made of keratin -- the same substance as human fingernails. The scales are produced by the epidermis, the outer layer of skin. As the snake grows, the number and the pattern of its scales stay the same, although a snake's scales are shed many times over the course of its life.
Unlike people, who shed worn-out skin constantly in tiny pieces, snakes shed all of their scales and outer skin in one piece during a process called molting. When the skin and scales start to wear down from time or injury, the epidermis begins to create new cells to separate the old skin from the developing inner layer. The new cells liquefy, making the outer layer soften. When the outer layer is ready to shed, the snake scrapes the edges of its mouth against a hard surface, such as a rock, until the outer layer begins to fold back around its head. It continues scraping and crawling until it is completely free of the dead skin. The molting process, which takes about 14 days, is repeated after anywhere from a few days to a few months.
Like people, snakes grow quickly until they reach maturity, which can take one to nine years; however, their growth, though much slowed after maturity, never stops. It's a phenomenon known as indeterminate growth. Depending on the species, snakes can live from four to more than 25 years.