Rattlesnake

Rattlesnake, common name for venomous North American snakes of the pit viper subfamily, that are recognized by a horny rattle at the end of the tail, which is shaken vigorously to warn off intruders. A new rattle section is added each time the snake moults, which may be as often as four times a year. Older parts of the rattle often become worn and break off, so that the number of rattles is not, as popularly believed, an accurate indication of age.

Like all pit vipers, the rattlesnake has deep, heat-sensitive pits on the sides of the face, which help in hunting warm-blooded prey. Two venom glands, one in each cheek, are connected by ducts to the base of two long, hollow fangs that fold against the roof of the mouth when not in use. The venom may contain a number of protein-based toxins. One, a neurotoxin, depresses the action of the heart and lungs; another, a haemotoxin, damages blood vessels and other tissue. Rattlesnakes feed primarily on small mammals and reptiles. Like most pit vipers, they give birth to live young.

The two genera of rattlesnakes, Sistrurus and Crotalus, are distinguishable by their head coverings. Snakes belonging to Sistrurus, which include the massasauga and the pygmy rattlesnake, have large plates on the top of their heads. Snakes belonging to the genus Crotalus have head coverings consisting mostly of small scales. Sistrurus species are relatively small, rarely exceeding 1 m (3 ft) in length. They range from southern Canada to central Mexico. The genus Crotalus contains both the largest and the smallest species of rattlesnake, which range from southern Canada to Argentina. The timber rattlesnake, about 1.5 m (5 ft) in length, ranges from New Hampshire to Texas, but its numbers have been largely reduced because of habitat destruction and unscrupulous collecting. The eastern diamondback is found in the south-eastern United States and is the largest species of rattlesnake, with exceptional individuals reaching about 2.4 m (8 ft) in length. Other species include the western diamondback rattlesnake, found in the south-western United States and northern Mexico; the prairie rattlesnake, found in the western United States; the red diamondback rattlesnake, found in southern California and Baja California; and the sidewinder, found in the deserts of the south-western United States and easily recognized by the horn-like scales over its eyes. The tropical, or neotropical, rattlesnake, which ranges from Mexico to Argentina, has the most extensive distribution of any rattlesnake. See Viper.

Scientific classification: Rattlesnakes belong to the subfamily Crotalinae of the family Viperidae. The massasauga is classified as Sistrurus catenatus and the pygmy rattlesnake as Sistrurus miliarius. The timber rattlesnake is classified as Crotalus horridus, the eastern diamondback as Crotalus adamanteus, the western diamondback rattlesnake as Crotalus atrox, the prairie rattlesnake as Crotalus viridis, the red diamondback rattlesnake as Crotalus ruber, the sidewinder as Crotalus cerastes, and the tropical, or neotropical, rattlesnake as Crotalus durissus.