|A common adder snake on a slope with mosses, grasses and other vegetation. Half its body is coiled in a figure of eight to allow striking|
| Vipera berus|
They are not highly dangerous: the snake is not aggressive and usually only bites when alarmed or disturbed. Bites can be very painful, but they are rarely fatal. The snake is not threatened, though it is protected in some countries.
Adults grow to about 60 centimeters (24 in) in length. The largest, at around 90–104 (35–41 in), are found in Scandinavia. In France and Great Britain, the maximum size is 80–87 centimeters (31–34 in), weighing from 50 grams (1.8 oz) to about 180 grams (6.3 oz).
Unusually for snakes, the sexes can be seen by their colour. Females are usually brownish with dark-brown markings, the males are pure grey with black markings.
The species has two morphs. The common pattern is the one with dark stripe with crossbars along the back, on a lighter body. The melanistic morph is very dark all over. The dark morph is more common in females. Polymorphism is usually maintained by natural selection.
The adder has a wide range. It lives in across Eurasian. In several European countries it is the only native venomous snake.
The adder's diet is mainly small mammals such as mice, voles, shrews and even weasels and moles. Sometimes, they eat slow worms and lizards. They feed on amphibia, such as frogs, newts, and salamanders. There have been reports of adders eating birds, especially nestlings and eggs. Adders are ovoviviparous. Once they reach about 30 cm (1 ft) in length, their diet becomes adult.
They are protected by law in the U.K., (Wildlife and Countryside Act 1981), and by the Berne Convention (the Berne Convention on the Conservation of European Wildlife and Natural Habitats). It is an offence to harm them.
- Appleby L.G. 1971. British snakes. London: Baker. Template:Catalog lookup linkScript error: No such module "check isxn".
- Ford E.B. 1965. Genetic polymorphism. All Souls Studies, Faber & Faber, London.
- Ford E.B. 1975. Ecological genetics. 4th ed, Chapman and Hall, London.