Viper

Vipers are a group of snakes known as the family Viperidae. They live in many parts of the world, but you won't find them in places like Antarctica, Australia, Hawaii, Madagascar, or Ireland, along with some other isolated islands. All vipers are venomous and have special long, hinged fangs that help them inject venom deeply into their prey.

These snakes are sometimes called viperids. The word "viper" comes from a Latin word that also means viper. It might be linked to ideas about giving live birth, which is a trait many vipers share. Scientists think the earliest vipers separated from other snake groups during a time called the early Eocene, millions of years ago. They are part of a larger group known as Caenophidia.

Description

A rattlesnake skull, showing the long fangs used to inject venom

Vipers have special fangs that help them inject venom. These fangs fold back into their mouths when not in use, allowing them to have long fangs in a small mouth. When a viper strikes, its mouth opens wide and the fangs extend to inject venom into its prey. This venom helps to break down the prey's tissues so it can be digested more easily. Vipers can also give "dry bites" where no venom is injected, which helps them save their venom for when they really need it.

Most vipers have a stout body, a triangle-shaped head, and special eyes that can adjust to different light levels. They are often active at night and wait quietly for their prey to come close before striking. Some vipers give birth to live young, while others lay eggs.

Geographic range

Vipera berus pictured in Laukaa, Finland, in May 2020

Viperid snakes live in many parts of the world, including the Americas, Africa, Eurasia, and South Asia. In the Americas, they are found south of 48°N. In the Old World, they live almost everywhere except in Siberia, Ireland, and areas north of the Arctic Circle, except for parts of Norway and Sweden. They are not found in the wild in Australia. The common adder, a type of viper, is the only venomous snake in Great Britain.

Venom

The western diamondback rattlesnake Crotalus atrox, the venom of which contains proteins allowing the snake to track down bitten prey

Viper venoms contain special proteins that break down tissues and affect blood flow, causing pain, swelling, and damage to blood vessels. Unlike other snake venoms that mainly affect nerves, viper venom helps to immobilize prey and aids in digestion by breaking down molecules like fats and proteins.

These snakes can control how much venom they inject based on the situation. Larger vipers can deliver more venom, and the type of prey also influences how much venom is used. After biting, some vipers can track their prey using proteins in their venom, which helps them find the animal again to eat it.

Subfamilies

The type genus for vipers is Vipera Laurenti, from the year 1768. This helps scientists classify and study these snakes.

Subfamily	Taxon author	Genera	Common name	Geographic range
Azemiopinae	Liem, Marx & Rabb, 1971	1	Fea's vipers	Myanmar, southeastern Tibet across South China (Fujian, Guangxi, Jiangxi, Guizhou, Sichuan, Yunnan, Zhejiang) to Northern Vietnam
Crotalinae	Oppel, 1811	22	Pit vipers	In the Old World from Eastern Europe eastward through Asia to Japan, Taiwan, Indonesia, Peninsular India and Sri Lanka; in the New World from southern Canada southward through Mexico and Central America to southern South America
Viperinae	Oppel, 1811	13	True or pitless vipers	Europe, Asia, and Africa

Sensory organs

Heat-sensing pits

Pit vipers have special pits near their nostrils that can sense heat. These pits detect the heat given off by warm-blooded animals, helping vipers find their prey even in the dark. The pits send signals to the brain, combining heat detection with vision to help the snake understand its surroundings.

Taxonomy

Scientists have different ideas about who first named the viper family. Most experts agree that a man named Laurenti used a word meaning "viper" but did not mean it as a family name. Instead, they say another scientist named Oppel gave the family its name, even though a third scientist, Gray, was the first to use a certain term related to it.