Vipers are snakes in the family Viperidae, found in most parts of the world, except for Antarctica, Australia,[2] Hawaii, Madagascar, New Zealand, Ireland, and various other isolated islands.

[5] All viperids 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.

Almost all vipers have keeled scales, a stocky build with a short tail, and a triangle-shaped head distinct from the neck, owing to the location of the venom glands.

In the Old World, viperids are located everywhere except Siberia, Ireland, and north of the Arctic Circle in Norway and Sweden.

Viperid venoms typically contain an abundance of protein-degrading enzymes, called proteases, that produce symptoms such as pain, strong local swelling and necrosis, blood loss from cardiovascular damage complicated by coagulopathy, and disruption of the blood-clotting system.

This is in contrast to elapid venoms, which generally contain neurotoxins that disable muscle contraction and cause paralysis.

[7] Due to the nature of proteolytic venom, a viperid bite is often a very painful experience and should always be taken seriously, though it may not necessarily prove fatal.

Even with prompt and proper treatment, a bite can still result in a permanent scar, and in the worst cases, the affected limb may even have to be amputated.

In defensive bites, the amount of venom injected may be determined by the size or species of the predator (or antagonist), as well as the assessed level of threat, although larger assailants and higher threat levels may not necessarily lead to larger amounts of venom being injected.

This important adaptation allowed rattlesnakes to evolve the strike-and-release bite mechanism, which provided a huge benefit to snakes by minimizing contact with potentially dangerous prey animals.

These pits have the ability to detect thermal radiation emitted by warm-blooded animals, helping them better understand their environment.

Rather, it is attributed to Oppel, based on his Viperini as a distinct family group name, despite the fact that Gray was the first to use the form Viperinae.