subcaudals are paired, numbering 32–46 in males and 23–38 in females. The colour pattern varies, ranging from very light-coloured specimens with small, incomplete, dark dorsal crossbars to entirely brown ones with faint or clear, darker brown markings, and on to melanistic individuals that are entirely dark and lack any apparent dorsal pattern. However, most have some kind of zigzag dorsal pattern down the entire length of their bodies and tails. The head usually has a distinctive dark V or X on the back. A dark streak runs from the eye to the neck and continues as a longitudinal series of spots along the flanks. Unusually for snakes, it is often possible to distinguish the sexes by their colour. Females are usually brownish in hue with dark-brown markings, the males are pure grey with black markings. The basal colour of males will often be slightly lighter than that of the females, making the black zigzag pattern stand out. The melanistic individuals are often females. Distribution and habitat Vipera berus has a wide range. It can be found across the Eurasian land-mass; from northwestern Europe (Great Britain, Belgium, Netherlands, Scandinavia, Germany, France) across southern Europe (Italy, Serbia, Albania, Croatia, Montenegro, Bosnia and Herzegovina, North Macedonia, Bulgaria, and northern Greece) and eastern Europe to north of the Arctic Circle, and Russia to the Pacific Ocean, Sakhalin Island, North Korea, northern Mongolia and northern China. It is found farther north than any other snake species. The type locality was originally listed as 'Europa'. Mertens and Müller (1940) proposed restricting the type locality to Uppsala, Sweden and it was eventually restricted to Berthåga, Uppsala by designation of a neotype by Krecsák & Wahlgren (2008). In several European countries, it is notable as being the only native venomous snake. It is one of only three snake species native to Britain. The other two, the barred grass snake and the smooth snake, are non-venomous. Sufficient habitat complexity is a crucial requirement for the presence of this species, in order to support its various behaviours—basking, foraging, and hibernation—as well as to offer some protection from predators and human harassment. It is found in a variety of habitats, including: chalky downs, rocky hillsides, moors, sandy heaths, meadows, rough commons, edges of woods, sunny glades and clearings, bushy slopes and hedgerows, dumps, coastal dunes, and stone quarries. It will venture into wetlands if dry ground is available nearby and thus