Vipers

Vipers are a family of venomous snakes found in most parts of the world, with the exception of Antarctica, Australia, Hawaii, Madagascar, as well as various other isolated islands, and north of the Arctic Circle. All have long, hinged fangs that permit deep penetration and injection of snake venom. The name \"viper\" refers to the trait viviparity (giving live birth) common in vipers, but not in snakes at large. All vipers have a pair of relatively long solenoglyphous (hollow) fangs that are used to inject venom from glands located towards the rear of the upper jaws, just behind the eyes. 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. During a strike, the mouth can open nearly 180°. These snakes can decide how much venom to inject depending on the circumstances. In cases with nonprey, such as humans, vipers may give a dry bite (not inject any venom). A dry bite allows the snake to conserve its precious reserve of venom, because once it has been depleted, time is needed to replenish it, leaving the snake vulnerable. Typically, vipers are nocturnal and ambush their prey.