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Rattlesnakes (Crotalus viridis viridis)are distinctly American serpents. There are 15 species of rattlesnakes in the United States and 25 in Mexico. Rattlesnakes are usually identified by their warning rattle — a hiss or buzz — made by the rattles at the tip of their tails. Rattlesnakes occur only in North and South America and range from sea level to perhaps 11,000 feet (over 3,000 m) in California and 14,000 feet (4,000 m) in Mexico, although they are not abundant at the higher elevations. Young or small species of rodents comprise the bulk of the food supply for most rattlesnakes. When a rattlesnake strikes its prey or enemy, the paired fangs unfold from the roof of its mouth. The greatest danger to humans from rattlesnakes is that small children may be struck while rolling and tumbling in the grass. Most species of rattlesnakes are not considered threatened or endangered.