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Rattlesnakes and their 320+ relatives are considered to be the most advanced of all snakes. Vipers have hollow fangs that fold back against the roof of the mouth when not in use and which can inject venom the manner of a hypodermic needle. From the fantastically-marked Gaboon Viper to the highly diverse Rattlesnakes, some of which provide parental care to their young, Vipers have captured the imaginations of people worldwide.

Important Note: Vipers are suitable for display in zoos only, and should never be kept in private collections. The following information, and that contained in the descriptions of the various species, is intended to introduce the reader to their incredible diversity, and is not meant to serve as a care guide. Those interested in working with venomous snakes are advised to seek careers as herpetologists or professional zookeepers.

Vipers are venomous snakes, and all are capable of delivering deadly bites. Snake venom is constantly evolving in response to prey animal defenses, and we know little about the toxins produced by many species. Due to these facts, and because individual sensitivities and other factors can greatly affect one’s reaction to a bite, even those species that are sometimes referred to as “mildly venomous” must be considered as capable of causing human fatalities. It is impossible for a private snake owner to adequately prepare for or treat a venomous snakebite, or, prior to a bite, to arrange for treatment in a hospital.

Overview

Pit Vipers (i.e. rattlesnakes, Eyelash Vipers), True Vipers (i.e. the Gaboon Viper) and their relatives are classified in the family Viperidae. To date, 321 species have been described. All bear hollow, venom-conducting teeth, or fangs, at the front of the mouth. Attached to the maxillary bone, these fangs fold back against the roof of the mouth and are rotated forward when in use. Venom is injected in the manner of a hypodermic needle, after which the snake backs away from its prey. The bitten animal is tracked and consumed once it has expired. Unlike cobras and other Elapids, which must hold onto their prey for a time in order to induce venom, Vipers are rarely injured by struggling victims.

The Three Viper Subfamilies

Crotalinae

The 224 species in the subfamily Crotalinae, which includes the rattlesnakes and other Pit Vipers, are considered to be the world’s most highly-evolved snakes. A sophisticated thermo-receptive pit, located between the eye and nostril, detects the heat produced by birds and mammals. This organ, far more refined than boa and python heat receptors, provides a thermal image (size, location) of nearby animals.

Rattlesnakes reach their greatest diversity in the Southwestern USA and Mexico. Thirteen of the 36 known species inhabit Arizona alone. Four species - the Eastern Diamondback, Eastern Massasauga, Pigmy and Timber Rattlesnakes - range into the eastern third of the USA; South America hosts 2 species, the Neo-Tropical and Uracoan Rattlesnakes. The rattlesnakes’ closest relatives are North America’s Copperheads and Cottonmouths or Water Moccasins. Other Pit Vipers inhabit Central and South America, Asia and Europe.

Viperinae

The 95 members of the subfamily Viperinae, known as “True Vipers”, live in Africa, Asia and Europe. Among them we find the European Adder, Vipera berus, which ranges north of the Arctic Circle, and the Puff Adder, Bitis arietans, responsible for more fatalities in Africa than any other snake.

Azemiopinae

The subfamily Azemiopinae contains 2 poorly-studied East Asian species, the Fea’s Viper, Azemiops feae, and the White-headed Fea Viper, A. kharini, which was only discovered in 2013.

Size

Vipers range in size from the 12-inch-long Meadow Viper, Vipera ursinii, to Africa’s Gaboon Viper, Bitis gabonica, which may reach 7 feet in length and sport a circumference of 20 inches, and South America’s 8-12 foot-long Bushmaster, Lachisis muta muta.

Viper Venom

Viper venom is far more complex than was once believed. Haemotoxins, which damage blood cells, blood vessels and body tissues, predominate in most that have been studied. However, all have neurotoxic components as well, along with the enzyme Hyaluronidase, which speeds venom diffusion.

Some Vipers produce venoms that are specific in their actions. For example, the venom of Timber Rattlesnakes living in the Northeastern USA is most effective against Gray Squirrels (a common prey item) while southern populations produce venom tailored to subdue cottontail rabbits. North American Kingsnakes, various ground squirrels and other animals that hunt or are hunted by Vipers have developed varying degrees of immunity to their venom.

A recent study revealed that venomous snakes (both Vipers and Elapids) bite approximately 4.5 million people worldwide each year, resulting in up to 100,000 deaths. People working outdoors in rural Sub-Saharan Africa are at greatest risk. Only 10% of the 1.5 million victims in this region receive antivenin - over 7,000 deaths and 14,000 limb amputations result.

Reproduction

With a single exception – the Bushmaster - all New World Vipers give birth to live young. Female rattlesnakes of some species protect their offspring until at least their first shed; Black-Tailed Rattlesnakes are able to recognize siblings after a 2 year separation.

Old World species tend also to bear live young, but several produce eggs. Parental care has not been well-studied.

Diet

Aided by thermo-receptive organs (please see above), rattlesnakes and other Pit Vipers generally hunt birds and mammals. The Cottonmouth or Water Moccasin, however, also takes fishes, frogs, snakes, and even carrion – including, in one instance, strips of fat from a road-killed pig!

Many True Vipers are generalists that consume a wide variety of mammals, birds, reptiles, and amphibians. The tiny Meadow Viper adds grasshoppers and other insects to its menu, while the massive Gaboon Viper takes adult Royal Antelopes and other sizable creatures.