Adder

• 1. Introduction

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  The adder, known to science as Vipera berus, lives farther north than any other snake. Its range reaches beyond the Arctic Circle. From there it spreads east across Russia to the Pacific Ocean, and it turns up on Sakhalin Island, in North Korea and in northern China.

  This is a venomous member of the viper family, yet it is neither huge nor aggressive. So why has such an unassuming animal gathered centuries of fear, remedies and myth? How does a cold-blooded creature live through winters in the far north? And is a snake with a range this vast truly safe from vanishing?

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• 2. Zigzags and Crosses

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  Most adders carry a zigzag stripe that runs down the whole body and out along the tail. Polish speakers named the snake żmija zygzakowata, meaning zigzag viper, after that pattern. A dark V or X is usually marked on top of the head. A dark streak also runs from the eye to the neck, then continues as a line of spots along the flanks.

  Unlike most snakes, adders can often be sexed by colour alone. Females are typically brown with dark brown markings. Males are a uniform grey with black markings. The male's base colour is often slightly lighter, so the black zigzag stands out more sharply.

  Some adders are pale, with only small, incomplete dark crossbars on the back. Darker ones show faint or clear brown markings. Melanistic adders are completely black with no visible back pattern, and these are often female.

  At midbody, an adder usually has 21 rows of strongly keeled dorsal scales, though 19, 20, 22 or 23 are rare. The scales look loosely attached to the skin. Those nearest the belly are twice as long as the ones along the midline. The head is fairly large and distinct, with almost flat, vertical sides.

  A typical adult is thick-bodied and about 60 cm long, including the tail, with an average of 55 cm. Mass ranges from 50 g to about 180 g. In France and Great Britain, the maximum length is 80-87 cm. Scandinavia produces the giants, which can pass 90 cm, and observers there have twice recorded specimens of 104 cm.

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• 3. Where Adders Live

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  In Britain, the adder is one of only three native snake species, and the only venomous one. The other two, the barred grass snake and the smooth snake, are harmless. Several other European countries also count the adder as their sole native venomous snake.

  The list of places it can be found is long. It occupies chalky downs, rocky hillsides, moors, sandy heaths, meadows, rough commons, woodland edges, sunny glades and scrubby hedgerows. It also lives on rubbish tips, coastal dunes and in stone quarries. Where dry ground is nearby, it will venture into wetlands and appear on the banks of streams, lakes and ponds.

  What the adder really needs is a varied landscape. Basking, foraging and hibernation all require different conditions. Complex habitat also gives some shelter from predators and from human disturbance.

  In southern France and northern Italy, adders are found either in low-lying wetlands or high in the mountains. In the Swiss Alps they may climb to about 3000 m. In Hungary and Russia they avoid open steppeland, where a related snake, V. ursinii, is more likely to occur. Yet in Russia the adder does live in the forest steppe zone.

  Even the scientific record of where the species belongs was once vague. The original type locality was listed only as Europa. Mertens and Müller proposed Uppsala, Sweden in 1940. A neotype designated by Krecsák and Wahlgren in 2008 narrowed it to Berthåga, in Uppsala.

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• 4. Habits of a Timid Snake

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  At the slightest hint of danger, an adder slips into the undergrowth. Once all is quiet, it often returns to exactly the same spot. Some individuals reveal themselves with a loud, sustained hiss, probably to warn off intruders, and these are often pregnant females. When threatened, the front of the body is drawn into an S-shape ready to strike.

  In the north of its range, the adder is mainly active by day. Farther south it is said to be active in the evening, and in summer it may even move at night. It is mostly a ground dweller. Even so, it climbs banks and into low bushes to bask or look for prey.

  Winter brings a long sleep. In Great Britain, males hibernate for around 150 days and females for around 180. In northern Sweden, hibernation lasts eight to nine months. On mild days the snakes may emerge to bask where snow has melted, often crossing snow to get there. Roughly 15% of adults and 30-40% of juveniles do not survive the winter.

  When they hunt, adders go mainly for small mammals such as mice, rats, voles and shrews, along with lizards. They sometimes take slow worms, and even weasels, including least weasels and possibly juvenile stoats. Moles are on the menu too. Frogs, newts and salamanders are eaten as well. Nestling birds and eggs are taken from shrubs and bushes the snakes climb into. The diet shifts from place to place.

  Young adders start on nestling mammals, small lizards, frogs, worms and spiders. In the mountains, the alpine salamander is an important food. One study suggests it may make up almost half of the diet in some locations. Young snakes have been seen swallowing these salamanders in the early morning. Once an adder reaches about 30 cm in length, its diet begins to look like that of an adult.

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• 5. The Adder Dance

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  In Hungary, mating takes place in the last week of April, while in the north it comes in the second week of May. Mating has also been seen in June and even in early October. Nobody is sure whether autumn matings produce young.

  Males find females by following scent trails that can stretch for hundreds of metres in a day. If a female flees once found, the male chases her. Courtship is a synchronised display. The pair move side by side in a flowing motion, with tongues flicking along each other's backs and tails whipping about. Pairs stay together for a day or two afterwards.

  Rival males are driven off, and the contest has a name: the adder dance. It often begins with the same flowing movement. Then the two males face each other, raise the front of their bodies vertically and sway, each trying to push the other to the ground. The sequence repeats until one becomes exhausted and leaves to look for another mate.

  Appleby, writing in 1971, noted that he had never seen an intruder win one of these contests. He suggested that the defender grows so frustrated during courtship that he refuses to concede. There is no record of any biting during these bouts.

  Females often breed only once every two years, or once every three years when seasons are short and the climate is poor. Adders are ovoviviparous, so they give birth to live young. Birth usually comes in August or September, but can be as early as July or as late as early October. Litters range from three to 20.

  The young are usually born in a transparent sac and must free themselves from it. Sometimes they break out while still inside the mother. Newborns measure 14-23 cm, with an average of 17 cm, and carry a reserve of yolk. They shed their skin for the first time within a day or two. Females seem to take little interest in their offspring, though the young stay nearby for several days. Newborns also arrive with a fully working venom apparatus.

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• 6. Venom and Bites

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  Sweden records around 1,300 adder bites per year, and an estimated 12% of cases need hospital care. Human expansion across the snake's range has made bites relatively common. Domestic animals and livestock are frequent victims. In Great Britain, most cases occur between March and October.

  The venom is mainly proteolytic, haemotoxic and cytotoxic, and some populations may also have neurotoxic and neuromuscular effects. It is considered simpler than the venom of the related Vipera ammodytes, which could explain its milder effects. Composition probably varies by region and by individual snake.

  Measured against other vipers, the toxicity is relatively low. Minton reported values for mice in 1974 of 0.55 mg/kg intravenously, 0.80 mg/kg intraperitoneally and 6.45 mg/kg subcutaneously. One test found that 40-67 mg of adder venom was the minimum lethal dose for a guinea pig. Only 1.7 mg was needed with Daboia russelii venom. Yields are also low. Minton gives 10-18 mg for snakes 48-62 cm long, while Brown, in 1973, lists only 6 mg.

  The record bears this out. Britain had only 14 known deaths from adder bites between 1876 and 2005. The last was a five-year-old child in 1975. In 1998, a 39-year-old woman in Essex survived a near-fatal bite. An 82-year-old woman died after a bite in Germany in 2004, though it is unclear whether the venom was responsible. A 52-year-old man died in Sweden in 2023 after failing to seek treatment. In 2014, a 44-year-old British man was left seriously ill after a bite in Dalby Forest, Yorkshire.

  Local symptoms begin with severe, immediate pain. Swelling and tingling follow after a few minutes, though this can take up to 30 minutes. Within 24 hours the whole limb may be swollen and bruised. In children the swelling can spread across the whole body. Blood-filled blisters are uncommon, and necrosis is very rare.

  Systemic symptoms can appear within five minutes of the bite or be delayed by several hours. They include nausea, vomiting, abdominal colic, sweating, fever, lightheadedness and loss of consciousness. Blindness, shock and swelling of the face, lips and throat are possible. Left untreated, symptoms may persist or fluctuate for up to 48 hours. Some adults suffer discomfort and disability long afterwards, and full recovery can take up to a year. At least eight different antivenoms exist for this species.

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• 7. Names and Old Beliefs

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  The word adder comes from nædre, an Old English word for snake that was common in older Germanic languages. The Old English version of the Christian Scriptures used it for the devil and for the serpent in Genesis. In the 14th century, the Middle English 'a nadder' was rebracketed as 'an adder', just as 'a napron' became 'an apron' and 'a nompere' became 'an umpire'.

  Other languages carry their own labels. Welsh speakers say gwiber, from the Latin vīpera. In Denmark, Norway and Sweden the snake is hugorm, hoggorm or huggorm, roughly 'striking snake'. Finns call it kyykäärme, or simply kyy. Estonians say rästik and Lithuanians say angis. English alone has a dozen or so names, including northern viper, crossed viper and common cross adder. Even the scientific name hides a puzzle. The word berus was once used for a snake, possibly the grass snake Natrix natrix.

  Britain and other European countries gathered a great deal of folklore around the adder. Psalm 58, verse 4, speaks of a deaf adder, and the snake was long believed to be deaf. Oddly, oil made from adders was used as a cure for deafness and earaches. Females were thought to swallow their young when threatened and bring them up unharmed later. It was also said that an adder did not die until sunset.

  Cures for a bite were hands-on. People killed the snake responsible and rubbed its corpse or fat on the wound. Others held a pigeon or chicken against the bite, or jumped over water. Adders were thought to be drawn to hazel trees and repelled by ash.

  The Druids, it was believed, held that great frenzied gatherings of adders took place in spring. At the centre lay a polished rock called an adder stone, or Glain Neidr in Welsh. These stones were said to hold supernatural powers.

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• 8. A Shrinking Presence

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  In Great Britain, the Wildlife and Countryside Act 1981 makes it illegal to kill, injure, harm or sell adders. Norway has a similar law, the Viltloven or Wildlife Act 1981, and Denmark followed in 1981. Finland's Nature Conservation Act 9/2023 allows killing an adder when it cannot be captured and moved elsewhere. Sweden applies the same provision. In Switzerland, the snake is categorised as endangered. The Berne Convention lists the species in Appendix III, and it lives in many protected areas.

  The International Union for Conservation of Nature rates the adder as 'least concern', citing its wide distribution, presumed large population and broad range of habitats. Even so, it acknowledges that the population is decreasing. Recorded causes include loss of habitat, populations split by intense agriculture, and collection for the pet trade or venom extraction.

  A citizen science survey in the UK found evidence of extensive declines, especially among smaller populations. The most likely causes were public pressure and disturbance, fragmented habitat and poor habitat management. A further suggestion concerns game birds. Countryside estates release 47 million non-native pheasants and 10 million partridges each year, and this may be harming adders across the UK. Under that pressure, the possibility has been raised that the reptile could be extinct there by 2032.

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