Pit Viper Snake Facts

Pit vipers are venomous snakes with special heat-sensing organs.

Pit vipers are renowned for their large fangs and deadly venom, as well as for their ability to sense heat through pits located between their nose and eyes. Pit vipers make their home in a variety of habitats, from deserts to rain forests, and can be found around the world. Pit vipers are a diverse group of venomous snakes that possess many traits that make them stand out from other snakes.

Taxonomy, Range and Number

More than 200 species of vipers exist in the world, and all are members of the Viperidae family of snakes. Pit vipers are one of four sub-families called Crotalinae. Pit vipers can be further categorized into Old World and New World genera and species. Old World pit vipers can be found from eastern Europe to southeast Asia. New World pit vipers are found throughout the Americas.

Geography and Habitat

Within their broad geographic distribution, pit vipers can be found in a wide range of different environmental conditions. Most pit vipers are terrestrial and possess stout bodies; however, there are some species that are more slender and more adapted for arboreal habitats. Pit vipers can be found in many different biomes, from hunting in the trees of Asian rain forests to hiding in the sands of American deserts. Almost all vipers attempt to blend into their surrounding environment to surprise their prey when they attack.

Pit Organ

The pit organ is what makes this group of vipers distinguishable from other members of the Viperidae. Called loreal pits, the small openings between the nose and eyes of pit vipers lead to a highly sensitive organ that can detect minuscule temperature differences in the surrounding environment, allowing pit vipers to see prey in infrared in an otherwise dark environment. Although the heat sensitivity of pit vipers is an asset in hunting prey, the organ itself might have evolved as a defensive measure, allowing snakes to sense warm-blooded predators.

Fangs and Venom

All members of the viper family have a distinct venom delivery system. The fangs of pit vipers are retractable. When closed, the fangs rest against the upper portions of the viper's mouth. As it strikes, a pit viper's mouth opens almost 180 degrees, and the fangs are projected forward independently. The hollow fangs are connected to venom glands that are surrounded by strong muscles. Pit vipers can regulate how much venom they inject with each bite via the constriction of the venom muscles. The venom is hemotoxic and destroys blood vessels and muscle tissues around the bite, working as a digestive aid in addition to a poison.

Interesting Facts

The smallest pit viper is the hump-nosed pit viper (Hypnale walli) which grows to be only 1 foot in length. The largest pit viper is the Bushmaster (Lachesis muta muta), which can grow to be more than 12 feet long. The Bushmaster also is one of the few species of pit vipers that lays eggs. In North America, there are 18 endemic species of pit vipers, including rattlesnakes, copperheads and cottonmouths (also called water moccasins).

References

• Davidson College: Thermoreception in Snakes
• University of Florida: Venomous Snake FAQs
• "Pit Vipers"; Adele Richardson; 2004
• University of Pittsburgh: Snakes of North America
• Molecular Phylogenetics and Evolution: Bayesian Mixed Models and the Phylogeny of Pitvipers

Resources

• Wayne's Word: Antivenins for Bites of Venomous Snakes
• Nature: Molecular Basis of Infrared Detection by Snakes