Science, Tech, Math › Animals & Nature All About Vipers (Viperidae) Share Flipboard Email Print kuritafsheen / Getty Images Animals & Nature Reptiles Amphibians Birds Habitat Profiles Mammals Wildlife Conservation Insects Marine Life Forestry Dinosaurs Evolution View More By Laura Klappenbach Ecology Expert M.S., Applied Ecology, Indiana University Bloomington B.S., Biology and Chemistry, University of Illinois at Urbana-Champaign Laura Klappenbach, M.S., is a science writer specializing in ecology, biology, and wildlife. our editorial process Laura Klappenbach Updated April 17, 2019 Vipers (Viperidae) are a group of snakes known for their long fangs and venomous bite. Vipers include true vipers, bush vipers, rattlesnakes, pit vipers, adders and night adders. Venomous Fangs The fangs of vipers are long and hollow and enable the snake to inject venom into animals that it bites. Venom is produced by and stored in glands located at the back of the snake's upper jaw. When the snake's mouth is closed, the fangs recede into a thin membrane and fold against the roof of the snake's mouth. When a viper bites its victim, the bones of the jaw rotate and flex so that the mouth opens at a wide gape angle and the fangs unfold at the last moment. When the snake bites down, muscles that encase the venom glands contract, squeezing venom out through ducts in the fangs and into their prey. Types of Venom Several different types of venom are produced by the various species of vipers. Proteases consist of enzymes that break down proteins. These enzymes cause a variety of effects in bite victims including pain, swelling, bleeding, necrosis, and disruption of the clotting system. Elapid venoms contain neurotoxins. These substances disable prey by disabling muscle control and causing paralysis. Proteolytic venoms contain neurotoxins to immobilize prey as well as enzymes that break down molecules in the victim's body. Head Shape Vipers have a triangular-shaped head. This shape accommodates the venom glands at the back of the jaw. Most vipers are slender to stout-bodied snakes with a short tail. Most species have eyes with elliptical pupils that can open wide or close down very narrowly. This enables the snakes to see in a wide range of light conditions. Some vipers have keeled scales—scales with a ridge in their center—while others have smooth scales. 26 Types There are currently about 26 species of vipers that are considered vulnerable, endangered or critically endangered. Some of the rarest vipers include the golden lancehead and the Mt. Bulgar viper. Like most snakes, vipers appear not to care for young after hatching. Most species of vipers give birth to live young but there are a few species that lay eggs. Vipers occur in terrestrial habitats throughout North, Central and South America as well as in Africa, Europe, and Asia. There are no vipers native to Madagascar or Australia. They prefer terrestrial and arboreal habitats. The range of vipers extends further north and further south than any other group of snakes. Vipers feed on a variety of small animal prey including small mammals and birds. Classification Vipers belong to the snake family. Snakes are among the most recently evolved of the main reptile lineages alive today. Their evolutionary history remains somewhat murky, though—their delicate skeletons do not preserve well and as a result, few fossil remains of ancient snakes have been recovered. The earliest known snake is Lapparentophis defense which is estimated to have lived about 130 million years ago, during the early Cretaceous. The viper family includes about 265 species. Vipers are classified into one of four groups: Azemiopinae: Fea's viperCausinae: night addersCrotalinae: pit vipersViperinae: true vipers The Viperinae, also known as the Old World vipers, are short and stocky snakes. They have a wide, triangular head and rough, keeled scales. Their coloration is dull or cryptic providing them with good camouflage. Most members of this group give birth to live young. Pit vipers are distinct from other vipers due to a pair of heat-sensitive pits located on either side their face between the eyes and nostrils. Pit vipers include the world's largest viper, the bushmaster, a snake native to Central and South American rainforests. The bushmaster can grow as long as 10 feet. Copperhead snakes are also pit vipers. Of all vipers, the rattlesnakes are among the most easily recognized. Rattlesnakes have a rattle-like structure at the end of their tail formed out of old layers of the terminal scale that do not fall off when the snake molts. When shaken, the rattle serves as a warning signal to other animals.