Viper

Viper, common name for snakes in a family of venomous snakes, characterized by a pair of long, hollow fangs, usually with reserve fangs beside them, in the front of the upper jaw. The fangs fold back against the palate when not in use and quickly swing forward to strike, injecting a deadly venom that kills prey and also serves as a defense. The viper generally has a broad, triangular head, and the eyes have vertical pupils. Most vipers give birth to living young from eggs hatched inside the mother's body.

Vipers are distributed throughout most temperate and tropical regions of the world, except Australia. They occur from lowlands to elevations of more than 4500 m (14,800 ft), from deserts to rain forests, and even in arctic regions.

Vipers are usually divided into two groups: the true vipers—including certain adders and asps, the horned and Gaboon vipers of Africa, and the Indian viper—and the pit vipers, which have a distinctive heat-sensitive pit between the eye and nostril, and which include the rattlesnakes, copperhead, and cottonmouth.

Scientific classification: Vipers make up the family Viperidae. The true vipers are classified in the subfamily Viperinae; the horned viper is classified as Bitis nasicornis, the gaboon viper as Bitis gabonica, and the Indian viper as Echis carinatus. The pit vipers are classified in the family Crotalidae, which contains the rattlesnakes, placed in the genera Crotalus and Sistrurus; the copperhead, Agkistrodon contortrix; and the cottonmouth, Agkistrodon piscivorus.