Subfamily CROTALINAE

Pit vipers

Pit vipers are among the most widespread of all venomous snakes, being distributed in the Americas, Asia, and Africa, but absent from Australia, Madagascar and Europe. They are characterized by the large pit that lies on the face between the eye and nostril. The pit is associated with a branch of the optic nerve allowing the snakes to literally see the infrared heat signature of warm-blooded prey, mainly mammals.

These are considered the most recently evolved and "advanced" snakes. Among their species are rattlesnakes, copperheads, cottonmouths, bushmasters, and fer-de-lance. The rattle which gives the subfamily its name (Crotalus is Greek for rattle) is found only in the genera Sistrurus (pygmy rattlers) and Crotalus (rattlesnakes), though a few species of Crotalus lack rattles.

Venom is usually primarily hemotoxic, but a few species (such as Crotalus scutellatus) have largely neurotoxic venom. Many species have a mixture, and venom composition may differ considerably among populations of the same species.