Common European Adder (Vipera berus): Facts and Habitat

Appearance: zigzag, eyes and colors

The adder is a thick-bodied snake with a fairly broad, flat-topped head, a short tail and strongly ridged (keeled) scales. Most adders have a bold zigzag or wavy stripe running from the neck to the tip of the tail, a row of dark spots along each side and a dark V or X-shaped mark on top of the head. A dark streak runs from the eye back toward the neck. The eyes are red to coppery, with vertical, slit-shaped pupils like those of a cat.

Unusually for a snake, males and females can usually be told apart by color. Males are silvery gray, whitish, cream or pale yellow with a jet-black zigzag that stands out sharply. Females are light brown, tan, reddish or copper with a darker brown zigzag. Newborn adders are often reddish brown.

Some adders are melanistic, meaning almost entirely black, with the pattern barely visible. These “black adders” are more frequent in cold, damp or mountainous regions, such as parts of the Alps and Scandinavia, and many of them are females. Dark skin may help them warm up faster in weak sunshine.

Like all vipers, the adder has long, hollow fangs at the front of the upper jaw. They are hinged and fold back against the roof of the mouth when not in use.

How big do adders get?

Adders are small snakes. Adults usually measure 55–65 cm (22–26 in) in total length, and the average is close to 55–60 cm (22–24 in). Females are generally larger than males. Maximum size varies across the range: in Britain and France the biggest adders reach about 80–87 cm (31–34 in), while in Scandinavia some exceed 90 cm (35 in), and two snakes of about 104 cm (41 in) have been reported there.

They are also light. A typical adult weighs about 50–100 g (1.8–3.5 oz), and the heaviest females weigh up to about 180 g (6.3 oz), especially when pregnant.

Habitat and range

No other viper covers so much of the globe. The adder lives from Great Britain, France, Belgium and the Netherlands east through Germany, Scandinavia, Poland and Russia, across Siberia to the Pacific coast, Sakhalin Island, North Korea, northern Mongolia and northern China. In southern Europe it is found mainly in mountains, such as the Alps and the Balkan ranges of Italy, Croatia, Serbia, Bulgaria and northern Greece. In Scandinavia and Finland it reaches beyond the Arctic Circle.

The adder needs a mosaic of habitats close together: open, sunny spots for basking, dense low cover such as heather, bracken or tussocky grass for shelter, and frost-free holes for winter. It lives on lowland heaths, moors, bogs, chalk downs, rough grassland, woodland edges and clearings, hedgerows, rocky hillsides, quarries and coastal dunes. In the Swiss Alps it climbs to about 3,000 m (9,800 ft).

In Britain the adder occurs from Cornwall to the north of Scotland, but only in scattered pockets. It is absent from Ireland and the Isle of Man. For more detail, see Where do adders live? and How far north do adders live?

Diet and hunting

Adders are ambush and stalking predators. Adults feed mainly on small mammals, especially voles, mice and shrews, along with lizards, frogs, newts and the nestlings of ground-nesting birds. Young adders start with tiny prey such as baby mice, small lizards and froglets.

The adder strikes, injects venom and lets go. The prey usually runs a short distance before collapsing, and the snake then follows its scent trail by flicking its forked tongue. It swallows food whole, headfirst. A large meal can last a snake several weeks, and pregnant females often eat very little.

Behavior and hibernation

The adder is a cold-adapted snake that spends a large part of the year hibernating. In Britain, males hibernate for around 150 days and females for around 180, usually from about October to February or March. In northern Sweden, hibernation lasts 8–9 months. Adders often winter in the same den, or hibernaculum, year after year: an old burrow, a gap among tree roots or a crevice in a bank. Dozens may share a good site.

On emerging, adders spend hours basking, flattening their bodies to soak up the sun. They are mostly active by day in the north and more active at dusk and in the evening in warmer areas. Adders are shy and slip away into cover at the first sign of footsteps, often returning to the same basking spot once all is quiet. When cornered, they may hiss loudly and pull the front of the body into an S-shape, ready to strike.

Reproduction and the adder dance

Males emerge from hibernation first and shed their skin in spring before searching for females by following their scent trails. Rival males then compete in the famous “dance of the adders”, rearing up face to face and trying to push each other to the ground. There is no record of males biting each other during these bouts. Read more in Why do male adders dance?

Mating usually takes place in April or May, and females in many populations breed only every two or even three years, because they need time to rebuild their fat reserves. Adders are live-bearers: the eggs stay inside the mother, and she gives birth to 3–20 young, usually in August or September. The babies are born in a thin, transparent membrane, from which they wriggle free. They have working venom from birth and shed their skin for the first time within a day or two.

Young adders are independent at once, although they may stay near their mother for a few days. They must find a place to hibernate before they have eaten much, and many do not survive their first winter. Adders become mature at about 3–4 years old.

Venom and bites

Adder venom mainly damages tissue and blood vessels around the bite, and the amount injected is small. Bites are painful and cause swelling, and they can make people, especially young children and older adults, seriously ill, so every bite needs emergency medical care. Deaths are very rare. Britain recorded only 14 between 1876 and 2005, the last of them a five-year-old child in 1975. Sweden, where adders are common, sees around 1,300 bites a year.

Most bites happen when someone picks up or treads on an adder. Watching from a respectful distance, wearing boots in adder country and keeping dogs on a leash in spring and summer prevent almost all of them. If someone is bitten, call 999 (UK), 112 (EU) or 911 (US) and seek emergency medical help immediately. Our article Are adders dangerous? explains the real risk in more detail.

Predators and threats

Adders have many natural enemies. Birds of prey such as buzzards and golden eagles take them, as do herons, crows, storks, foxes, badgers and hedgehogs. Pheasants are also known to kill young adders, and some researchers suspect that the release of tens of millions of game pheasants each year contributes to declines in Britain.

People are the bigger threat. Heathland and moorland have been lost to farming, building and forestry, and the remaining patches are often small and isolated. Disturbance from walkers and dogs at basking and hibernation sites, poor habitat management, fires and road traffic also harm populations. Because adders move little and use traditional dens, small isolated groups can disappear quietly.

Conservation status

The IUCN Red List classes the common European adder as Least Concern because of its huge range, presumed large population and use of many habitats. It also notes that the population is decreasing. The species is listed under Appendix III of the Berne Convention.

In Great Britain, adders are protected under the Wildlife and Countryside Act 1981, which makes it illegal to kill, injure or sell them. The citizen science survey Make the Adder Count found that most monitored British sites hold small populations and that these small populations are the ones most likely to be declining. The adder is also protected in Norway, Denmark, Finland and Sweden, and it is listed as endangered in Switzerland.

Myths and facts

• Myth: adders swallow their young to protect them. This old belief has no evidence behind it. Young adders may stay near the mother for a few days, but they are not carried or swallowed.
• Myth: adders are deaf. Adders have no external ears, but they have inner ears and can pick up low-frequency sound and ground vibrations.
• Myth: adders chase people. Adders are timid and flee if they can. Bites nearly always follow handling or accidental contact.
• Fact: the adder is a snake of the north. It lives farther north than any other snake species and survives winters that last most of the year.

Relationship with people

The adder has a long place in European folklore. Its English name comes from the Old English nædre, meaning snake: “a nadder” gradually became “an adder”. The Druids were said to believe in an “adder stone” formed by gatherings of snakes in spring, perhaps inspired by groups of adders basking or dancing near their dens.

Today the adder is a flagship species for heathland conservation in Britain and the Netherlands, and spring adder walks in places like the New Forest and Dorset heaths draw many wildlife watchers. To compare it with the snake people most often confuse it with, see adder vs grass snake.