Which venomous snake is the only one native to the British Isles?

The common European adder is the only venomous snake native to the British Isles.

Also called the common adder or common viper, Vipera berus is Britain’s sole native venomous snake. It is one of only three native snake species in Great Britain; the other two, the grass snake and smooth snake, are non-venomous. The species also ranges widely across Europe and into northern Asia.

Adders are generally shy and are more likely to flee than attack. Bites usually happen when a snake is stepped on, handled, or deliberately disturbed. Their venom can cause pain, swelling, bruising, and other symptoms, but fatalities in Britain are extremely rare, especially when medical care is obtained.

The adder’s zigzag dorsal pattern is familiar, although some individuals—particularly black adders—can appear almost entirely dark. A common mix-up is assuming that every snake found in Britain is harmless, or confusing the adder with the grass snake. The grass snake is larger in many areas and often has a pale collar, but it lacks venom and poses no comparable bite risk.