Reptiles
European Adder
Vipera berus · also called common adder, common European viper, crossed viper
The European adder is a snake of extremes and contradictions: the most widely distributed snake on the planet, the only snake that lives inside the Arctic Circle, Britain’s only venomous reptile, and, despite all that, a shy, cold-loving animal whose bite has not killed anyone in Britain in fifty years.
Overview
Vipera berus is a short, thick-bodied viper, usually 60 to 75 cm long, with a clear head, vertical pupils, and a bold dark zigzag down the back. Males are typically silvery grey, females brown or coppery, and some adders are entirely black. It ranges across Europe and northern Asia, from Britain to the Pacific, in heath, moor, woodland edges, bogs, and mountains, and it hunts small mammals, lizards, and frogs with a venomous strike.
A cold-climate snake
The adder is built for cool conditions. In the north it hibernates for up to eight months, often communally, and emerges in early spring to bask. Males perform the upright wrestling contest known as the dance of the adders for access to females, and the female gives live birth to 3 to 20 young in late summer, an effort so costly in a cold climate that she breeds only every two or three years.
A modest bite
Of Britain’s three native snakes, only the adder is venomous, and its venom is made for small prey. A bite to a healthy adult brings severe pain and swelling but rarely lasting harm, and there has been no confirmed British death since 1975, though children, elderly people, and dogs are at greater risk.
Status
The adder is Least Concern across its huge range, but the trend is downward at the edges. In Britain it is considered to be in serious long-term decline, driven by the loss and fragmentation of open habitat, disturbance of hibernation sites, and its very slow breeding rate.
European Adder: common questions
How dangerous is an adder bite?
Much less than its reputation suggests, but not trivial. Adder venom is designed for small prey, and a bite to a healthy adult usually causes intense local pain, rapid swelling that can spread up the whole limb, bruising, nausea, and sometimes a drop in blood pressure. Most people recover fully within a few days, often with antivenom and observation in hospital. Serious reactions and lasting harm are uncommon, but they are more likely in children, elderly people, and anyone with a strong allergic response, and bites to the face or a blood vessel are worse. There has been no confirmed death from an adder bite in Britain since 1975, though dogs bitten on the nose or paw do sometimes die.
How do I identify an adder?
Look for a fairly short, thick-bodied snake, usually 60 to 75 cm long, with a distinct head, a vertical slit pupil, and a bold, continuous dark zigzag running down the middle of the back. The ground colour is typically silvery grey with a black zigzag in males and pale brown or reddish with a dark brown zigzag in females, and some adders are wholly black, in which case the zigzag is hidden. The similar but harmless grass snake is longer, more slender, greener or greyer, has a round pupil, and shows a yellow-and-black collar behind the head rather than a zigzag. Slow worms are legless lizards, smaller, shinier, and without any zigzag.
Where and when are you likely to see an adder?
Adders like a mix of open, sunny ground for basking and dense cover for hiding, so classic places are lowland heath, moorland, bog edges, open woodland and rides, railway embankments, coastal dunes, and rough hillsides. They are most visible in early spring, from about March to May, when they emerge from hibernation and spend long periods basking near the den before dispersing to summer feeding areas. On a warm morning an adder may be coiled in the open at the edge of a path or bramble patch; by midday in high summer it is usually hidden. They are shy and will move away if they detect footsteps in time.
Why are adders declining in Britain?
The adder is still widespread in Britain but many populations are small and shrinking, and surveys suggest a serious long-term decline, with the snake already lost from large parts of central England. The main causes are the loss and fragmentation of heath, rough grassland, and other open habitats, which leaves populations isolated and unable to mix; disturbance of hibernation and basking sites by development, forestry, intensive grazing, and heavy public access with dogs; and, historically, deliberate killing out of fear. Because females breed only every two or three years and young adders are vulnerable, populations recover very slowly once they fall.