Because they outgrow it. A snake's body continues to grow most of its life, but its skin, which consists of thousands of scales, never grows. When the skin becomes too tight, the snake "molts" or sheds it, making room for a new, larger skin that has developed under the old one. The snake removes the old skin by rubbing against a rough surface like a rock or a tree.
Diamondback Survivors Premieres Wednesday, January 29, 2003 at 8 p.m. ET/PT on the National Geographic Channel Work with a rattlesnake expert to learn how America's largest venomous snakethe diamondbackhas been able to thrive in the wake of human encroachment.