Viper Snake

Reviewed by: BD Editors

A blue-colored Sri Lankan pit viper curled up on.
A blue-colored Sri Lankan pit viper.

Kingdom Animalia
Phylum Chordata
Class Reptilia
Order Squamata
Family Viperidae
Subfamily  4
Genus 32
Species > 200
Length The smallest is 10 in (25 cm) the largest can reach 10 ft (3 m)
Lifespan Various
Social Structure Solitary
Status Fifty-seven species are near threatened, vulnerable, endangered, critically endangered, or extinct in the wild.
Preferred Habitat Found in a range of habitats across the world
Average Litter Size Varies, most species have live young
Main food item Small mammals, birds, lizards, and eggs.
Main predators Large mammals and birds.

The Basics

The viper snake is one of over 200 species that belong to the family Viperidae. Species from this large family are found all over the world, except for Antarctica, Australia, north of the Arctic Circle, New Zealand, Madagascar, and some island clusters such as Hawaii. Viper snakes are very diverse and are found in a variety of habitats ranging from mountains to deserts and jungles.

The viper snake generally has a large, triangular-shaped head because of large venom glands located behind their eyes. They have short, stocky bodies compared to other snakes, such as cobras and mambas. Although they can often appear sluggish, these short, powerful bodies give them more power to strike and ambush their prey. Vipers are usually camouflaged and blend in with their environment.

All species are venomous, although some are more dangerous than others. A viper’s venom is mostly hemotoxic, meaning that it acts on the blood, unlike the venom of elapid species, which is neurotoxic and affects the nervous system.

Vipers eat a variety of food depending on the size of the snake. Prey includes small mammals, birds, lizards, and eggs. Vipers will detect their prey through chemical signals and lie in wait until it can ambush it. The viper will inject its venom and let its prey go, waiting for it to die. This method of hunting protects the snake from any damage the prey species might cause it. When their victim is dead, the snakes swallow it whole.

Most species of viper are viviparous and give birth to live young. There are a few exceptions to this, including the six species of night adders.

A bush viper with its mouth open, displaying its fangs
A bush viper

The Four subfamilies of Vipers

There are four subfamilies of the viper snake: Azemiopinae, Causinae, Crotalinae, and Viperinae.

Azemiopinae is a subfamily of viper that contains just one genus and two species; Azemiops feae and Azemiops kharini, also known as the Fea’s Viper or mountain viper. These vipers are different from the other vipers in appearance. They have an elliptical-shaped head that has enlarged scales. This genus is so different in appearance from the other viper snake species that it has previously been categorized as belonging to two different families of snakes entirely – the elapid and colubrid families. Scientific research has shown that it is most closely related to the crotaline vipers or pit vipers.  It is found in the tropical mountain regions of south-central China, northern Burma, and northern Vietnam.

The Causinae subfamily consists of one genus (Causus) and six species that are endemic to sub-Saharan Africa. Commonly known as the night adders, these snakes can grow to around 24 to 36 in long (60 – 90 cm). Unlike most viper snakes, night adders are oviparous, which means that they lay eggs. The snakes lay about 24 eggs at a time, which hatch after four months. These snakes have large venom glands but don’t always inject venom when hunting prey. If a person is bitten by one of these snakes, the venom doesn’t move around the body but does cause localized swelling at the site of the bite. There have been no reports of human death from a night adder bite.

Crotalinae is a subfamily of snakes known as pit vipers and includes cottonmouth snakes, copperhead snakes, and rattlesnakes. There are more than 150 species in this subfamily, which are mainly found across North and South Ameria, and in parts of East and Central Asia. This is the only subfamily of viper snakes found in the Americas. Pit vipers are characterized by a heat-sensing pit organ that is located between the eye and the nostril on either side of the head. Many people are afraid of these snakes, but they rarely attack humans and are an essential part of the food chain, feeding on agricultural pests such as rabbits, mice, and rats.

The Viperinae subfamily is known as the true vipers and is made up of 12 genera and approximately 66 species. These snakes are found throughout Africa, Asia, and Europe. These vipers lack the heat-sensing pit organ that is found in their sister family, Crotalinae. Common members of this family include puff adders, common European adders, and bush vipers.

A common Europea adder coiled up ready to strike
A common European adder.

Interesting Insights from the Viper Snake.

Viper snakes are a diverse family of snakes that are found in a wide variety of habitats. There are a number of differences between these snakes that make them adapted to their environment and also several biological adaptations that link them. Let’s take a closer look at three of them.

Hinged Fangs

Vipers are known for their long, hollow fangs which can fold up and lie against the roof of their mouth. Their fangs connect to venom glands that are located behind the eyes. Venom can travel down from these glands and through the hollow teeth to be injected into the prey animal when the viper bites.

One incredible feature of a vipers fangs is that they are rotatable, both together and independently. This means that the snakes can wait until the last second before they bite to erect their fangs. These snakes can open their mouths really wide, up to 180 degrees, which gives them the space to be able to rotate their fangs. When they aren’t in use, the teeth stay folded up in the roof of the snake’s mouth. This means that these fangs can grow relatively long!

The venom of viper snakes is predominantly hemotoxic, although some species do have neurotoxic venom. In general, hemotoxic venom can have adverse effects on the cardiovascular and hematic systems of the animal bitten. It can cause a dramatic fall in blood pressure and prevents the blood from clotting, causing the victim to start hemorrhaging. This can cause severe internal bleeding, tissue damage, and organ failure. If you ever get bitten by a viper snake, you should seek medical attention right away!
A gaboon viper with its head raised
A Gaboon viper

Pit Organ

The pit organ is specific to the Crotalinae family of viper snakes and is located between the snake’s eyes and nostrils. This organ gives the snake the fantastic ability to sense infrared heat to track prey. This is because of a protein – TRPA1 – that is found in the organ.
The accumulation of this protein in the pit organ allows the snakes to have a sixth sense – night vision – which comes from the ability to detect infrared heat. As the majority of the snakes in this family are nocturnal, this is a very useful adaptation to have! Once the snakes have bitten their prey, they can track them until they succumb to the effects of the venom.

Cite This Article

MLAAPAChicago Editors. "Viper Snake." Biology Dictionary,, 03 Aug. 2020, Editors. (2020, August 03). Viper Snake. Retrieved from Editors. "Viper Snake." Biology Dictionary., August 03, 2020.

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