The head is fairly large and distinct, the sides of which 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 2 (rarely 1) small scales. Dorsally, there are usually 5 large plates: a squarish frontal (longer than wide, sometimes rectangular), 2 parietals (sometimes with a tiny scale between the frontal and the parietals), and 2 long and narrow supraoculars. The latter are large and distinct, each separated from the frontal by 1-4 small scales. The nostril is situated in a shallow depression within a large nasal scale. The eye is relatively large -- equal in size or slightly larger than the nasal scale -- but often smaller in females. Below the supraoculars there are 6-13 (usually 8-10) small circumorbital scales. The temporal scales are smooth (rarely weakly keeled). There are 10-12 sublabials and 6-10 (usually 8-9) supralabials. Of the latter, the numbers 3 and 4 are the largest, while 4 and 5 (rarely 3 and 4) are separated from the eye by a single row of small scales (sometimes 2 rows in alpine specimens).
Midbody there are 21 dorsal scales rows (rarely 19, 20, 22 or 23). These are strongly keeled scales, except for those bodering the ventral scales. These scales seem loosely attached to the skin and lower rows become increasingly wide; those closest to the ventral scales are twice as wide as the ones along the midline. The ventral scales number 132-150 in males and 132-158 in females. The anal plate is single. The subcaudals are paired, numbering 32-46 in males and 23-38 in females.
The color pattern varies, ranging from very light-colored specimens with small incomplete dark dorsal crossbars to melanistic individuals that are entirely dark and lack any apparent dorsal pattern. However, most have some kind of zigzag dorsal pattern down the entire length of the body and tail. The head usually has a distinctive dark V or X on the back. A dark streak runs from the eye to the neck and continues as a longitudinal series of spots along the flanks.
The word "adder" was nædre in Old English; in the 14th century a nadder was, like a napron, rebracketed as an adder. It appears with the generic meaning of serpent in the older forms of many Germanic languages, and is thus used in the Old English version of the Christian Scriptures for the devil, the serpent of the Book of Genesis.
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 3000 m. 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.
Generally speaking, this is not an aggressive species, tending to be rather timid and biting only when cornered or alarmed. Many people are only bitten after stepping on them. They will usually disappear into the undergrowth at a hint of any danger, but will return once all is quiet, often to the same spot. Occasionally, individuals will reveal their presence with a loud and sustained hissing, hoping to warn off potential aggressors. Often, these turn out to be pregnant females. When threatened, the front part of the body is drawn into a S-shape to prepare for a strike.
This is a cold-adapted species that hibernates in the winter. In Great Britain, males and females hibernate for about 150 and 180 days respectively. However, in northern Sweden hibernation lasts 8-9 months. On mild winter days, they may emerge to bask where the snow has melted and will often travel across snow. Nevertheless, about 15% of adults and 30-40% of juveniles die during hibernation.
Juveniles will eat nestling mammals, small lizards and frogs, as well as insects, worms and spiders. Once they reach about 30 cm in length, their diet begins to resemble that of the adults.
Males find females by following their scent trails, sometimes tracking them for hundreds of meters a day. If a female is found and flees, the male follows. Courtship involves side-by-side parallel "flowing" behavior, tongue flicking along the back and excited lashing of the tail. Pairs stay together for one or two days after mating. Males chase away their rivals and engage in combat. Often, this also starts with the aforementioned flowing behavior before culminating in the dramatic "adder dance." In this act, the males confront each other, raise up the front part of the body vertically, make swaying movements and attempt to push each other to the ground. This is repeated until one of the two becomes exhausted and crawls off to find another mate. Interestingly, Appleby (1971) notes that he has never seen an intruder win one of these contests, as if the frustrated defender is so aroused by courtship that he refuses to lose his chance to mate. There are no records of any biting taking place during these bouts.
Females usually give birth in August-September, but sometimes as early as July, or as late as early October. Litters range in size from 3 to 20. The young are usually born encased in a transparent sac from which they must free themselves. Sometimes, they succeed in freeing themselves from this membrane while still inside the female. The neonates, measuring 14 to 23 cm (average of 17 cm), are born with a fully functional venom apparatus and a reserve supply of yolk within their bodies. They shed their skins for the first time within a day or two. Females do not appear to take much interest in their offspring, but the young have been observed to remain near their mothers for several days after birth.
Mallow et al. (2003) describe the venom toxicity as being relatively low compared to other viper species. They cite Minton (1974) who reported the LD50 values for mice to be 0.55 mg/kg IV, 0.80 mg/kg IP and 6.45 mg/kg SC. As a comparison, in one test the minimum lethal dose of for a guinea pig was 40-67 mg, but only 1.7 mg was necessary when Daboia russelii venom was used. Brown (1973) gives a higher subcutaneous LD50 range of 1.0-4.0 mg/kg. All agree that the venom yield is low: Minton (1974) mentions 10-18 mg for specimens 48-62 cm in length, while Brown (1973) lists only 6 mg.
Relatively speaking, bites from this species are not highly dangerous. In Britain there have been only 14 known fatalities since 1876; the last a 5-year-old child in 1975. An 82-year-old woman died following a bite in Germany in 2004, although it is not clear whether her death was due to the effect of the venom. 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. The length of recovery varies, but may take up to a year.
Local symptoms include immediate and intense pain, followed after a few minutes (but perhaps by as much as 30 minutes) by swelling and a tingling sensation. Blisters containing blood are not common. The pain may spread within a few hours, along with tenderness and inflammation. Reddish lymphangitic lines and bruising may appear, and the whole limb can become swollen and bruised within 24 hours. Swelling may also spread to the trunk, and with children, throughout the entire body. Necrosis and intracompartmental syndromes are very rare.
Systemic symptoms resulting from anaphylaxis can be dramatic. These may appear within 5 minutes post bite, or can be delayed for many hours. Such symptoms include nausea, retching and vomiting, abdominal colic and diarrhoea, incontinence of urine and faeces, sweating, fever, vasoconstriction, tachycardia, lightheadedness, loss of consciousness, shock, angioedema of the face, lips, gums, tongue, throat and epiglotis, urticaria and bronchospam. If left untreated, these symptoms may persist or fluctuate for up to 48 hours. In severe cases, cardiovascular failure may occur.
At least eight different antivenins are available against bites from this species.
|Subspecies||Taxon author||Common name||Geographic range|
|V. b. berus||(Linnaeus, 1758)||Common European adder||Norway, Sweden, Finland, Latvia, Estonia, Lithuania, France, Denmark, Germany, Austria, Switzerland, Northern Italy, Belgium, Netherlands, Great Britain, Poland, Czech Republic, Slovakia, Hungary, Romania, Russia, Mongolia, north-west China (north Xinjiang)|
|V. b. bosniensis||Boettger, 1889||Balkan cross adder||Balkan Peninsula|
|V. b. sachalinensis||Zarevskij, 1917||Sakhalin Island adder||Russian Far East (Amur Oblast, Primorskye Kray, Khabarovsk Kray, Sakhalin Island), North Korea, north-east China (Jilin)|