Vipers are a family of snake (the Viperidae) found throughout the world except in Australia and Madagascar. Their bite is venomous, which they use to catch small animals, such as lizards, small mammals and birds, that constitute their diet. Viper venom can be fatal to humans if treatment is not sought. Like many snakes, vipers have special organs that allow them to sense infrared.
The Viperidae family is divided into four subfamilies:
- Azemiopinae Liem, Marx & Rabb, 1971 (Fea's vipers) with only one species: Azemiops feae living in Myanmar, southeastern Tibet across southern China (Fujien, Guangxi, Jiangxi, Kweichow, Sichuan, Yunnan, Zhejiang) to northern Vietnam.
- Causinae Cope, 1859 (night adders) living in Sub-Saharan Africa
- Crotalinae Oppel, 1811 (pit vipers: rattle snakes, bushmaster, cottonmouth, copperhead, jararacas) - In the Old World from eastern Europe eastward through Asia to Japan, Taiwan, Indonesia, peninsular India and Sri Lanka. In the New World from southern Canada southward through Mexico and Central America to southern South America.