Adder

Adder facts at a glance

How big is a adder?

An adult adder measures 80 cm long — about 46% of the height of an average adult person (1.73 m) — and weighs around 100 g, a small fraction of an average adult’s body weight (70 kg).

What is a group of adders called?

Explore more animal collective nouns and baby animal names .

Appearance and identification

The adder is a short, thick-set snake, usually 60 to 90 cm long and about 100 g, with a distinctive dark zigzag stripe running the length of its back. Colours range from silvery-grey in many males to reddish-brown in females, and some individuals are entirely black. A V or X marking often shows on the head, and the eyes have vertical, cat-like pupils typical of vipers. This bold dorsal pattern makes the adder one of Britain's most recognisable reptiles.

Venom and its bite

As a true viper, the adder has hinged fangs that fold back against the roof of the mouth and swing forward to inject venom in a rapid strike. The venom is designed to subdue small prey and is only mildly dangerous to humans; bites cause pain and swelling but are very rarely fatal. Most bites occur when a snake is trodden on or handled, and it will always try to escape first. Anyone bitten should seek medical advice, as reactions can occasionally be severe.

Diet and hunting

The adder is a carnivore that preys on small mammals such as voles and mice, along with lizards, frogs, and nestling birds. It hunts by ambush, striking prey with a venomous bite and then following the scent trail until the animal succumbs. After swallowing prey whole it may rest for days to digest. Young adders take smaller fare, including insects and slow-worms, until they are large enough for bigger prey.

Habitat and behaviour

Adders favour open, sunny habitats including heathland, moorland, woodland edges, and coastal dunes across much of Europe and into Asia. Being cold-blooded, they rely on the sun and are often seen basking on banks or paths in spring to warm up. They are shy and secretive, quick to slither away into cover at the first sign of disturbance. Over winter they hibernate communally in sheltered spots, emerging around March to bask and breed.

Reproduction and lifespan

Adders mate in spring, when males perform a swaying "dance" as they wrestle rivals for access to females. Females give birth to live young in late summer, producing a litter of roughly three to twenty, rather than laying eggs. This ability to incubate young inside the body helps the species breed successfully in cool northern climates. Adders can live 10 to 15 years, though females often breed only every two or three years.

Conservation status

Globally the adder is listed as Least Concern by the IUCN, but in Britain many local populations are declining and fragmented. Loss and disturbance of heathland, intensive land use, and the isolation of small colonies are the main pressures. In the UK the species is legally protected against being killed or injured. Sympathetic habitat management and the linking of isolated sites are key to reversing local declines.

Did you know? Adder facts

• The adder, or common European viper, is the United Kingdom's only venomous snake, recognised by the bold dark zigzag stripe running down its back.
• Adders are venomous but not aggressive, and they bite people only in self-defence. Bites are painful and need medical attention, but they are very rarely fatal to healthy adults; children, older people, and pets are most at risk.
• Adders have a bold dark zigzag stripe down the back, dark side spots, and a 'V' or 'X' mark on the head, over a grey, brown, or reddish body. Some are all black, and they have red eyes with vertical pupils.
• Adders favour heathland, moorland, woodland edges, and coastal dunes across Europe and Asia. They are the only venomous snake native to Britain and range farther north than any other snake.
• Adders are carnivores that ambush small mammals such as voles and mice, as well as lizards, frogs, and ground-nesting birds' eggs and chicks. They use venom to subdue prey and swallow it whole.
• Conservation: Least Concern (IUCN).

Diet & feeding

Adder feeds primarily as a carnivore (small mammals, lizards, frogs). The adder is venomous, but it is a shy snake that bites people only when trodden on, cornered, or handled. Its venom is designed to immobilise small prey, and serious harm to a healthy adult is rare — most bites cause pain and swelling rather than la

Adaptations

• The adder is venomous, but it is a shy snake that bites people only when trodden on, cornered, or handled. Its venom is designed to immobilise small prey, and serious harm to a healthy adult is rare — most bites cause pain and swelling rather than lasting injury. All bites should still be treated as a medical emergency, as reactions vary; children, older people, and pets are most at risk, and antivenom is available where needed.
• Adders are unmistakable thanks to the dark zigzag band along the back and a row of dark spots down the sides, set against a grey, brown, or reddish ground colour; some individuals are entirely black. There is usually a dark 'V' or 'X' mark on the head and red eyes with vertical pupils. Males tend to be greyer and females browner, and the species is relatively stocky for its modest length.

Behaviour & ecology

• The adder is venomous, but it is a shy snake that bites people only when trodden on, cornered, or handled. Its venom is designed to immobilise small prey, and serious harm to a healthy adult is rare — most bites cause pain and swelling rather than lasting injury. All bites should still be treated as a medical emergency, as reactions vary; children, older people, and pets are most at risk, and antivenom is available where needed.
• Adders are unmistakable thanks to the dark zigzag band along the back and a row of dark spots down the sides, set against a grey, brown, or reddish ground colour; some individuals are entirely black. There is usually a dark 'V' or 'X' mark on the head and red eyes with vertical pupils. Males tend to be greyer and females browner, and the species is relatively stocky for its modest length.
• Adders are ambush predators that feed on small mammals such as voles and mice, along with lizards, frogs, and the eggs and chicks of ground-nesting birds. They use venom to subdue prey, then track and swallow it whole. Cold-blooded and dependent on the sun, adders bask to warm up and hibernate through winter, often returning to the same communal sites year after year.

Communication

• Scent marking, body posture, and head-bobbing or tail signals communicate threat and dominance.
• Vocalisations are limited in many reptiles but hissing or bellowing occurs in some groups.

Habitat & range

Heathland, moorland, woodland edges, dunes

Ecological role

Adder acts as a predator that helps regulate prey populations and maintain balance in heathland, moorland, woodland edges, dunes.

Conservation status of the Adder

Sources & references

This guide is compiled and reviewed against established zoological and conservation references. Key sources for the Adder:

• IUCN Red List of Threatened Species

  Conservation status (Least Concern) reflects the IUCN Red List category for Vipera berus.

• iNaturalist — observations & photos

  Search citizen-science observations and community IDs for Vipera berus. Useful for range checks and recent sightings — not a substitute for formal Red List status.

• GBIF — occurrence data

  Global Biodiversity Information Facility species search for Vipera berus. Explore published occurrence records used in range research.

• IUCN Red List — Vipera berus.

  Conservation status (Least Concern) and population trends.

• Animal Diversity Web — Vipera berus. University of Michigan Museum of Zoology.

  Life history, morphology, and range.

• Wikipedia — Adder.

  General taxonomy and overview (cross-check primary sources).

• Global Animal Guide editorial standards

  How we research, source, review, and update every guide for accuracy.