The adder is the only venomous snake native to Britain. Adders have the most highly developed venom injecting mechanism of all snakes, but they are not aggressive animals. Adders will only use their venom as a last means of defence, usually if caught or trodden on. No one has died from adder bite in Britain for over 20 years. With proper treatment, the worst effects are nausea and drowsiness, followed by severe swelling and bruising in the area of the bite. Most people who are bitten were handling the snake. Treat adders with respect and leave them alone.
Adder (Vipera berus)
Adders are relatively common in areas of rough, open countryside and are often associated with woodland edge habitats. They are less inclined to disappear into the surrounding undergrowth when disturbed and so are probably the most frequently seen of the three British snakes. The best time to see them is in early spring when they emerge from their hibernation dens. By mid April, the males have shed their dull winter skin and are ready to mate. There is a lot of frenzied activity on warm days, with males looking for females and occasionally wrestling with other males for supremacy. The ‘dance of the adders’ was thought to be a mating display, but it is a larger male attempting to drive off a smaller one. The snakes writhe around each other in an impressive way, often covering the ground at great speed.
Following mating, females seek out a suitable place to give birth, often travelling over 1 kilometre from the hibernation site. Births take place in late August / early September. Unlike most reptiles, adders do not lay eggs. Young snakes are born about the size and shape of an earthworm, but a perfect miniature of the adult snake.
During the autumn, adult snakes follow scent trails left by other adders to find their way back to the hibernation site, which is often used by many snakes over several years. The young adders tend to hibernate in the area where they were born. Their survival largely depends on the severity of the weather in the following winter.
Adders usually eat small rodents, such as the short-tailed vole. They will also eat lizards, frogs and newts, and have been seen taking young from the nests of ground nesting birds. When hunting, adders strike swiftly at the prey, injecting a lethal dose of venom. They then wait until the prey dies before starting the often lengthy swallowing process. Like all snakes, adders eat their prey whole, their teeth are designed to grip the prey as it is swallowed. Their jaws are linked by extensible connective tissue so each of the four main bones can move independently. This means they are able to swallow items much larger than the width of their head. The lower ends of the ribs are not joined as in most animals and can also open out considerably. The adder’s digestive fluid is amazingly powerful and will digest the flesh and bones of their prey almost completely. Only the hair and teeth of rodents pass through intact.
Young adders are threatened by a variety of predators, including birds of prey such as the common buzzard and sometimes adult snakes. Others may be killed and eaten by rodents while in hibernation. Adders are protected by law against being killed or injured through human activity.
Most adders are distinctively marked with a dark zigzag running down the length of the spine and an inverted ‘V’ shape on the neck. Males are generally white or pale grey with a black zigzag. Females are a pale brown colour, with a darker brown zigzag. But some adders are entirely black and can be mistaken for some other species.
How we manage our woods
Most of the woods managed by the Forestry Commission are suitable for adders. The way we manage the woods – cutting down older trees and planting young trees – provides excellent habitat. For the first 10 years as the young trees grow, adders can build up large populations unseen. Then as the tree canopy closes overhead, the snakes seek out the light and warmth that is available at the woodland edge.