Pit Vipers occur in both Hemispheres, and current evidence suggest a Eurasian origin for the subfamily. All of the molecular and anatomical studies done suggest that the subfamily is monophyletic (it had one ancestor, and therefore the heat sensing pit evolved only once). The sister to the pit vipers is an unusual Chinese viper, Azemiops fea. There are about 18 genera and about 150 species currently recognized and it seems likely that these numbers will increase. While most pit vipers are terrestrial some are arboreal, and at least one shows a tendency to be semi-aquatic. New World pit vipers are also monophyletic and are presumably derived from a clade containing the Old World Gloydius and Ovophis monticola. A member of this clade invaded the Western Hemisphere presumably via the Bering Land Bridge, probably during the Late Cretaceous or early Tertiary. (See Parkinson et al. 2002 In: Biology of the Vipers.) Many of these snakes pose a threat to human health and need to be treated with respect.

Samuel Purchas (1625) described the venon apparatus and deadly nature of the jararacucu (probably a neotropical Bothrops) in his book The Relations of the World, and the Religious observed in all Ages and in all Places discovered since the Creation. Book 1. London.

"...they are ten Spannes long: they have great Tuskes hidden in the Mouth along their Gummes, and when they bite they stretch them like a Finger of the Hand; they have their Poyson in their Gummer, their Teeth crooked, and a Stroake vpon them whereby the Poison runneth, Others say they have it within the Tooth which is hollow within, It hath so vehement a Poison that in foure-and-twentie Houres and lesse it killeth a Man."

The Copperhead, Agkistrodon contortrix (Linnaeus, 1766). Photographed in Jackson County, Illinois.

For more photos of pit vipers in the Agkistrodon Complex click on the photo.

The Terciopelo, Bothrops asper (Garman, 1884). Photographed in Costa Rica.

For more photos of Western Hemisphere pit vipers in the genera Bothriechis, Bothrops, and Lachesis click on the photo.

The Western Diamondback Rattlesnake, Crotalus atrox Baird and Girard, 1853. Photographed in Cochise County, Arizona.

For more photos of Rattlesnakes in the genera Crotalus and Sistrurus click on the photo.

Borneo Pit Viper, Tropidolaemus subannulatus (Gray, 1842). A juvenile, photographed in the Danum Valley, Sabah, Malaysia (Island of Borneo).

For more photos of Asian Pit Vipers click on the photo.