Pit Viper

Pit vipers are venomous snakes having a pair of heat-sensing pits in the front of the head, and hollow erectile fangs used to transmit venom. These snakes characteristically have broad, lance-shaped heads and vertical pupils. Terrestrial species are typically stout-bodled and marked with patterns of brown, gray, yellow, pink or black; tree in color, with markings of yellow, red, or black. The pit vipers are closely related to the true vipers and are usually classified as a subfamily, Crotalinae, of the viper family, Viperidae.

The pit organ is located between the nostril and the eye on each side of the head. It is supplied with nerves and blood vessels and is partially enclosed in a cavity in the side of the maxillary, a bone of the upper jaw. The pit has a thermo receptor function and is sensitive to infrared radiation; it is capable of responding to change in temperature of only fraction of a degree. Thus pit vipers can detect the presence of animals with body temperatures only slightly different from that of the environment.

In North America, pit vipers are represented by about 31 species of Rattlesnae (genera Crotalus and Sistrurus) and by the Copperhead and Water Moccasin, or cottonmouth (Agkistrodon). The greatest diversity of pit vipers occur in Central and South America, with 2 or 3 species of Rattlesnake, about 60 species of lance-heads, such as the Fer-De-Lance (Bothrops), and the Bushmaster (Lachesis). In the Old World, pit vipers occur from the north Caspian region of Europe, across Asia to Japan and the Indonesian Archipelago.