Crotalidae (pit vipers; order Squamata, suborder Serpentes) A family of venomous snakes which are closely related to true vipers (Viperidae) but which have heat-sensitive pit organs just behind the nostrils. Their diet consists mainly of birds and small mammals. Tail-rattling mechanisms have been developed in advanced forms (rattlesnakes); these are formed from loosely connected horny segments more of which are added to the ‘rattle’ at each moult. Crotalus horridus (timber rattlesnake) grows up to 1.8 m long and occurs in woodland in the eastern USA. C. cerastes (sidewinder) is small (up to 60 cm) and occurs in the deserts of the southwestern USA; it has a small horn above each eye and its common name is derived from its method of locomotion across soft sand: it proceeds diagonally by throwing its body forward in loops (‘sidewinding’ also occurs in some vipers). There are approximately 130 species in the family, occurring in the Americas and tropical Asia.

pit vipers See CROTALIDAE.