The Crotalinae, commonly known as pit vipers, or pit adders, are a subfamily of vipers found in Asia and the Americas. Like all other vipers, they are venomous. They are distinguished by the presence of a heat-sensing pit organ located between the eye and the nostril on both sides of the head. Currently, 23 genera and 155 species are recognized: These are also the only viperids found in the Americas. The groups of snakes represented here include rattlesnakes, lanceheads, and Asian pit vipers. The type genus for this subfamily is Crotalus, of which the type species is the timber rattlesnake, C. horridus.
Pit viper
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, New Zealand, Ireland, and various other isolated islands. They are venomous and have long, hinged fangs that permit deep penetration and injection of their venom. Three subfamilies are currently recognized. They are also known as viperids. The name "viper" is derived from the Latin word vipera, -ae, also meaning viper, possibly from vivus ("living") and parere, referring to the trait viviparity common in vipers like most of the species of Boidae.
Viperidae
A rattlesnake skull, showing the long fangs used to inject venom
Arabian Horned Viper from Arabian Peninsula
Vipera berus pictured in Laukaa, Finland, in May 2020