Vipers (Family Viperidae)

The Viperidae are a family of venomous snakes found all over the
world, except in Antarctica, Australia, New Zealand, Ireland, Mada-

gascar, Hawaii and the Arctic Circle. All have relatively long hinged

fangs that permit deep penetration and injection of venom. Four

subfamilies are currently recognized.

All viperids have a pair of relatively long hollow fangs that are used
to inject venom from glands located towards the rear of the upper
jaws. Each of the two fangs is at the front of the mouth on a short
maxillary bone that can rotate back and forth. When not in use, the
fangs fold back against the roof of the mouth and are enclosed in a
membranous sheath. The left and right fangs can be rotated together
or independently. During a strike, the mouth can open nearly 180°
and the maxilla rotates forward, erecting the fangs as late as possible
so as the fangs do not become damaged. The jaws close on impact

and powerful muscles that surround the venom glands contract to in-

ject the venom as the fangs penetrate. This action is very fast; in de-

fensive strikes it can be more a stab than a bite. Viperids use this

mechanism primarily for immobilization and digestion of prey. Sec-

ondarily it is used for self-defense, though in most cases with non-

prey items such as humans they are more likely to give a dry bite

(not inject any venom).

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