viper

Any front-fanged venomous snake of the family Viperidae. Vipers range in size from 30 cm/1 ft to 3 m/10 ft, and often have diamond or jagged markings. Most give birth to live young.

There are 150 species of viper. The true vipers, subfamily Viperinae, abundant in Africa and southwestern Asia, include the adder Vipera berus, the African puff adder Bitis arietans, and the horned viper of North Africa Cerastes cornutus. The second subfamily Crotalinae includes the mostly New World pit vipers, such as rattlesnakes and copperheads of the Americas, which have a heat-sensitive pit between each eye and nostril.