CLASS: Reptilia ORDER: Squamata FAMILY: Viperidae' adult size: 76 cm - almost 2 meters (30 in. - almost 6 feet); record is 2.13 m. distribution: Southwestern United States to southern Mexico. Rattlesnakes are unique to the Americas. habitat: Deserts, and grass, and scrublands to subtropical thorn scrub. diet: small mammals and birds. 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. The snake's tongue is harmless. The tips of the forked tongue pick up odorous particles from the snake's surroundings and transfer them to Jacobson's organ in the roof of the mouth, which is believed to combine the senses of taste and smell. Snakes do not have eyelids, but their eyes are still protected. Snake eyes are covered by a clear scale called the spectacle. The snake can see with protected eyes while it moves through grass or down dusty rodent burrows. The rattlesnake's rattle gets bigger every time it sheds its skin. A rattlesnake sheds its skin two to four times a year depending on its age and rate of growth. The rattle is actually modified scales and is made up of interlocking segments which click together when the snake vibrates its tail. The snake can vibrate its tail so rapidly that clicks of the rattle segments blur into a loud buzz. Rattlesnakes and alive. Some animals have eggs that develop inside the body of the mother before they are born. They are called ovoviviparous. Inside the egg, the developing rattlesnake is nourished by the yolk of the egg. Animals that lay eggs that develop outside of the mother's body, including most reptiles, are oviparous. Mammals are viviparous; their young are born alive and get nutrition directly through a connection to the mother's bloodstream.