Vipera berus, the common European adder or common European viper, is a venomous snake that is extremely widespread and can be found throughout most of Western Europe and as far as East Asia. Known by a host of common names including common adder and common viper, adders have been the subject of much folklore in Britain and other European countries. They are not regarded as especially dangerous; the snake is not aggressive and usually bites only when alarmed or disturbed. Bites can be very painful, but are seldom fatal. The specific name, berus, is New Latin and was at one time used to refer to a snake, possibly the grass snake, Natrix natrix.