Vipers

True vipers (family Viperinae) are found in the Old World and lack facial pits; this distinguishes them from the pit vipers of the Americas. Africa is the home of 30 of the 45 species of Old World vipers. Among the African vipers are the Gaboon viper (Bitis gabonicus) and the rhinoceros viper (B. nasicornis) that attain lengths of almost 6 ft (2 m) and have fangs that may be 2 in (5 cm) in length. There are green tree-vipers (Atheris), desert-dwelling sandvipers (Cerastes), and even a little-known worm-eating, burrowing viper (Adorhinos).

The deserts of north Africa and south Asia are home to a number of sandvipers, one of which is the notorious carpet viper (Echis carinatus). Although an adult of this snake may be little more than 1 ft (30 cm) in length, its bite is highly toxic and is responsible for many deaths, particularly in the desert regions of Pakistan and western India.

The small European viper or adder (Vipera berus), by contrast, is not dangerous to humans. Its bite has been described as "little worse than a bee-sting," and the few reported deaths are apparently due to over-treatment. This viper is notable in that it is one of very few snakes that ranges above the Arctic Circle in Sweden and Norway.

Some large vipers of the genus Vipera range from the eastern Mediterranean eastward through southern Asia. The ill-tempered and highly venomous Russell's viper (Vipera russelii) follows the rats into the rice fields when the fields are drained for harvesting. It is the major cause of fatal snake bites (killing perhaps 10,000 people annually) in Burma (Myanmar) and Thailand.