Rattlesnakes are unique to the Americas.
Deserts, and grass, and scrublands to subtropical thorn scrub. Rattlesnakes can sense warm-blooded prey in the dark. The deep pit between the rattlesnake's eye and nostril detects the heat of warm blooded prey. The rattlesnake has 2 of these pits and belongs to a group of snakes called pit vipers. Some boas and pythons have slit-like organs in their lips that serve a similar function.