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Puff adderPuff adder Vipers are venomous snakes with long, hollow fangs that fold back inside their mouths until they strike. Pit vipers are named after the deep pit, called a fossa, in the area between the eye and nostril on either side of the head. These are the external openings to heat-sensitive organs they use to locate their warm-blooded prey, and which give them a "picture" of it. The pit viper group includes rattlesnakes, moccasins and lanceheads. True, or old world vipers, such as the highly venomous puff adders, do not have these pits.

Rattlesnake coiled for attackRattlesnake coiled for attack


During a strike, the viper's mouth can open nearly 180°. The fangs are unfolded as late as possible to prevent damage. As the viper's jaws close around its victim and the fangs penetrate its flesh, powerful muscles rapidly inject the venom. Vipers use their venomous bite to paralyse their prey. It can also be used for self-defence, though in some cases they do not inject any venom.


Common adderCommon adderThe common adder, a true viper, is found across Europe and Asia. It is the only venomous snake in Great Britain. It bites only when alarmed or threatened and its venom is rarely fatal. It feeds chiefly on small mammals, birds, lizards and amphibians. Most adders have a zigzag pattern down the entire length of their bodies. The head usually has a dark "V" or "X" on the top. The common adder is adapted to cold climates (it is sometimes found north of the Arctic Circle) and hibernates in winter.

There are more than 200 species of viper, living all over the world except Antarctica, Australia, New Zealand, Ireland and Madagascar.

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