Vipera berus, commonly known as the common European adder and the common European viper, is a species of venomous snake in the family Viperidae. The species is extremely widespread, and thus can be found throughout much of Europe, and as far as East Asia. It is not regarded as especially dangerous; The specific name, berus, is Neo-Latin and was at one time used to refer to a snake, possibly the grass snake, Natrix natrix.
The common adder is found in different terrains, habitat complexity being essential for different aspects of its behaviour. It feeds on small mammals, birds, lizards, and amphibians, and in some cases on spiders, worms, and insects. The common adder, like most other vipers, is ovoviviparous, giving birth to live young. Females breed once every two or three years and litters are usually born in late summer to early autumn in the Northern Hemisphere. Litters range in size from three to 20 with young staying with their mothers for a few days. Adults grow to a total length (including tail) of and a mass of . Three subspecies are recognised, including the nominate subspecies, Vipera berus berus, described here. The snake is not considered to be threatened, though it is protected in some countries.
Taxonomy
There are three subspecies of V. berus that are recognised as being valid including the nominotypical subspecies.
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!Subspecies In the 14th century, 'a nadder' in Middle English was rebracketed to 'an adder' (just as 'a napron' became 'an apron' and 'a nompere changed into 'an umpire').
In keeping with its wide distribution and familiarity through the ages, Vipera berus has a large number of common names in English, which include:
:Common European adder, northern viper, adder, common adder, crossed viper, European adder, common viper, European common viper, cross adder, or common cross adder.
In Welsh, it is called gwiber, a name derived from Latin vīpera. In Denmark, Norway and Sweden, the snake is known as hugorm, hoggorm and huggorm, roughly translated as 'striking snake'. In Finland, it is known as kyykäärme or simply kyy, in Estonia it is known as rästik, while in Lithuania it is known as angis. In Poland the snake is called żmija zygzakowata, which translates as 'zigzag viper', due to the pattern on its back.
Description
Relatively thick-bodied, adults usually grow to in total length (including tail), with an average of .<!-- See discussion under "Mass" in talk -->
left|thumb|alt=Shows the front parts of two common adders. One snake has the normal colour while the other has melanistic colour/pattern form. The head of the normal snake is enclosed in a half-coil of the melanistic form.|V. berus: normal and melanistic colour patterns
The head is fairly large and distinct and its sides are almost flat and vertical. The edge of the snout is usually raised into a low ridge. Seen from above, the rostral scale is not visible, or only just. Immediately behind the rostral, there are two (rarely one) small scales.
Dorsally, there are usually five large plates: a squarish frontal (longer than wide, sometimes rectangular), two parietals (sometimes with a tiny scale between the frontal and the parietals), and two long and narrow supraoculars. The latter are large and distinct, each separated from the frontal by one to four small scales. The nostril is situated in a shallow depression within a large nasal scale.
The eye is relatively large, equal in size to or slightly larger than the nasal scale, but often smaller in females. Below the supraoculars, there are six to 13 small circumorbital scales, usually eight to 10. The temporal scales are smooth (rarely weakly keeled). There are 10–12 sublabials and six to 10 (usually eight or 9) supralabials. Of these, numbers 3 and 4 are the largest, while numbers 4 and 5 (rarely 3 and 4) are separated from the eye by a single row of small scales (sometimes two rows in alpine specimens).
In several European countries, it is notable for being the only native venomous snake. It is also one of only three native British snake species. The other two, the barred grass snake and the smooth snake, are non-venomous.
Sufficient habitat complexity is crucial for this species to be present, in order to support its various behaviours—basking, foraging, and hibernation—as well as to offer some protection from predators and human disturbance.
In much of southern Europe, such as southern France and northern Italy, it is found in either low-lying wetlands or at high altitudes. In the Swiss Alps, it may ascend to about . In Hungary and Russia, it avoids open steppeland; a habitat in which V. ursinii is more likely to occur. In Russia, however, it does occur in the forest steppe zone. A similar situation exists in Norway under the (The Wildlife Act 1981) and in Denmark (1981). In Finland (Nature Conservation Act 9/2023) killing an adder is legal if it is not possible to capture and transfer it to another location and the same provision also applies in Sweden. The common viper is categorised as 'endangered' in Switzerland, and is also protected in some other countries in its range. It is also found in many protected areas.
The International Union for Conservation of Nature Red List of Threatened Species describes the conservation status as of 'least concern' in view of its wide distribution, presumed large population, broad range of habitats, and likely slow rate of decline though it acknowledges the population to be decreasing. Reduction in habitat for a variety of reasons, fragmentation of populations in Europe due to intense agriculture practices, and collection for the pet trade or for venom extraction have been recorded as major contributing factors for its decline. A combination of public pressure and disturbance, habitat fragmentation and poor habitat management were considered the most likely causes of the decline. The release of 47 million non-native pheasants and 10 million partridges each year by countryside estates has also been suggested to have a significant impact on adder populations across the UK, with the possibility the reptile could be extinct by 2032.
Behaviour
thumb|alt=A slender adder lies in a half circle on the bare soil which has a few dried leaves. The black zig-zag pattern along the dorsal spine of the snake contrasts against the white borders forming a pattern resembling the teeth of an open zip. |V. berus male
This species is mainly diurnal, especially in the north of its range. Further south, it is said to be active in the evening, and it may even be active at night during the summer months. It is predominantly a terrestrial species, though it is known to climb up banks and into low bushes in order to bask or search for prey. to be consumed, especially nestlings and even eggs, for which they will climb into shrubbery and bushes. Generally, diet varies depending on locality. Once they reach about in length, their diet begins to resemble that of the adults. There is no record of any biting taking place during these bouts. although some populations may also have neurotoxic and neuromuscular effects. The venom is considered simpler than the related Vipera ammodytes, which could explain its comparatively mild effects and greater LD<sub>50</sub>.
Mallow et al. (2003) describe the toxicity of the venom as being relatively low compared to that of other viper species. They cite Minton (1974) who reported the values for mice to be 0.55 mg/kg IV, 0.80 mg/kg IP and 6.45 mg/kg SC. For comparison, one test found that the minimum lethal dose of venom for a guinea pig was 40–67 mg, whereas only 1.7 mg was necessary when Daboia russelii venom was used. and a 52-year-old male died in Sweden after failing to seek treatment in 2023. A 44-year-old British man was left seriously ill after he was bitten by an adder in the Dalby Forest, Yorkshire, in 2014. Even so, professional medical help should always be sought as soon as possible after any bite. Very occasionally bites can be life-threatening, particularly in small children, while adults may experience discomfort and disability long after the bite.
Local symptoms include severe and immediate pain, followed by swelling and tingling after a few minutes, although this may take up to 30 minutes. Blisters containing blood are uncommon. The pain may then spread within a few hours, accompanied by tenderness and inflammation. Red lymphangitic lines and bruising may appear, and the entire limb can become swollen and bruised within 24 hours. The swelling may also spread to the trunk and, in children, the whole body. Necrosis and intracompartmental syndromes are very rare. Remedies for adder "stings" included killing the snake responsible and rubbing the corpse or its fat on the wound, also holding a pigeon or chicken on the bite, or jumping over water. Adders were thought to be attracted to hazel trees and repelled by ash trees.