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All rattlesnakes (about 30 species) live within the western hemisphere, mostly in the southern parts of the US, Mexico, and Central America. All belong to the Viperidae family (pit vipers), have rattles, and are venomous.
Most rattlesnakes are 3-4 feet in length and, like all pit viper snakes, have pits on each side of their head that can sense heat. The pits allow them to detect a difference in temperature (to a fraction of a degree) so they can locate their warm-blooded prey. Below are more interesting rattlesnake facts.