In Denmark we only have a single species of venomous snake. As you already might have guessed; this is of course the common European adder, Vipera Berus, “the undisputed king of the heather”. Vipera berus are small, but true vipers; they belong to the family viperidae. They can be found widespread throughout most of Europe only with minor exceptions. The skin coloring varies between sexes, the males normally come in light shades of brown to steel grey, while female adders comes in more colorful in tones of brown and red. Some adult specimens are completely black, but they tend to be more rarely found in Denmark. European common adders are characterized by their zigzag pattern running the full length of their bodies on the dorsal side.
In Denmark they have a rather unfavorable environment which leaves our native populations of Vipera berus to be among some of the smallest/shortest common adders in Europe. Normally they don’t grow larger than 50 cm in length, even though females sometimes reach the maximum size. The Vipera berus species is arranged in three different subspecies, which are separated by their coloration and lepidotic traits.
Common names
The Common European adder has many names differing from each country. Throughout Europe it is called:Common European viper, European viper, adder, common adder, crossed viper, European adder, common viper, European common viper, northern viper, cross adder, or common cross adder. In Sweden and Norway it's called "hogorm or hoggorm", in Finland it's "kyykäärme". In Denmark we call it "hugorm". Hugorm directly translated literally means "strike-worm".
In Denmark we don't use the word viper even though its the best word to use by my opinion.
Behaviour
Vipera Berus is a terrestrial species of snake. I never saw a European common adder in a bush or in a tree, even though it's known to climb up banks and into low bushes in order to bask. In Denmark the snakes are active during the sun hours, but further south they are known to be active in the evening and can even be found during night in the summer months. The species is extremely well adapted to cold; actually it’s one of the most cold-resistant snakes in the world, therefore it hibernates during the winter, (as all of the other Danish species). Quote from Wikipedia: “In Great Britain, males and females hibernate for about 150 and 180 days respectively. In northern Sweden hibernation lasts 8–9 months. About 15% of adults and 30-40% of juveniles die during hibernation”.Vipera berus have a lot of natural enemies in Denmark, especially birds of prey and crows; we have many species of birds that prey on snakes. Martens and hedgehogs are also natural enemies. In general Vipera berus is a very docile species of snake, they will try to escape rather than risking a confrontation. If a common adder gets agitated or threatened it will hiss and flatten its body, if the snake can’t escape or are being followed/touched, it will eventually strike.
Diet
The common adder has a wide pallet of prey that can consist of many different things depending on their habitat. In order to survive in a cold environment such as Denmark, they can’t be picky. Most of their diet consists of small mammals such as mice, but also lizards and amphibians, such as frogs, newts and salamanders are eaten. Sometimes, slow worms are eaten as well - and even moles if possibly. Birds are also reported to be a part of Vipera Berus menu, especially nestlings and even eggs. Generally, the diet varies depending on locality. I believe that most vipers I encounter in Denmark lives of lizards and amphibians as their main staple. The prey are killed by envenomation and swallowed.The places I visit; I believe that most of the juveniles rely on Lacerta agilis and Zotaca vivipara. But in more wet areas Rana temporaria/arvalis and other frog’s must be the juvenile’s adders main source for food.
Habitat
Habitat is everything; complexity is a crucial requirement for the presence of the species. Common adders are found in a variety of different habitats, including: sandy heaths, rocky hillsides, moors, edges of woods, sunny glades, hedgerows and coastal lines. Normally they can be found on the banks of lakes, and ponds. It is crucial that both prey and hiding-places are present at all times for the adder to thrive. In Denmark many of the local populations is extremely isolated and exposed to human interfering. In some chases you can find local stocks of very few animals in very small microhabitats, such as some of our famous heather cliffs and closed quarries. If a local population is killed or removed it can be fatal for the stock. The common adder can be found almost everywhere in Denmark with minor exceptions.
Reproduction
The males search for females by scent trails. It has been recorded that the male can track a female for over hundred meters. Competitive males often engage in combat, some folks call this the "adder-dance". The two fighting males raise up the front of their body’s vertically and push each other down continually. They can keep on until one of them becomes exhausted and slither away. During the fight there is no biting or hissing. The males can stay together with the female for one or two days after the mating act. The act of mating normally takes place in April-may.
The snake is viviparous and the females usually give birth later during the summer, this can vary from place to place. The litters of snakes can range in size - from 3 to over 20. The neonates, can measure from 14 to 25 cm approx. (average of 17 cm). The young are usually born in a transparent egg-sac. Sometimes, they succeed in freeing themselves from this membrane inside the female. They are fully venomous when born. Females do not have any interest in their offspring, but the young have been observed to remain near their mothers for several days after birth. Each year the act of mating is one of my favourite behaviours to observe and photograph. It is always a joy to find neonates at the herp spots.
Denmark's only venomous snake
The snake is venomous and should only be approached by experienced field herpes or individuals familiar with handling venomous snakes. Bites from Vipera Berus are relatively uncommon in Denmark. Mostly it's tourists who get bitten by the snake. But domestic animals and livestock are frequent victims of the snakes bite as well. Normally this is because dog owner’s doesn’t even realize that adders are present in the Danish nature. The Danish government and nature agencies are not very good at informing the public about our herpefauna. Luckily, bites from the common adder are not considered highly dangerous. In Denmark we “only” had 7 fatal registered bite incidents during our countries history. Very occasionally, bites can be life threatening even though, particularly in small children. Adults may experience discomfort and disability long after the bite. Sometime bitten people can go into anaphylaxis shock which can be very dangerous and even fatal. The length of recovery varies a lot, but it might even take years.
Quote from venomdoc: "V. berus active venom components are mostly enzymes of a "toxic metalloproteinase" class (destructive enzymes with metal ions as cofactors) that cause primarily local tissue damage including the swelling and bruising frequently seen in envenomations. They apparently also produce a blood coagulating thrombin-like enzyme (TLE), but systemic bleedings are exceptionally rare in berus bites. Some local subpopulations like V.b.bosniensis are supposed to have neurotoxins in their venom (of the phospholipase A2 class, like Dabois russelli, or Crotalus d. terrificus or C. scutulatus, but much less abundant - so threatening neurotoxicity will not occur). The untreated mortality rate (UMR) after berus bites is estimated to be lower than 0.5%, i.e., less than 1 in 200 victims. For comparison, Echis ocellatus or sochureki, vipers of comparable size, produce UMR of 10-20 %!"
Quote from Wikipedia: “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, light-headedness, 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”.