Common European viper, Common adder, Common viper, Marlies, Prags, Bardas, European viper, Northern viper, Adder, Crossed viper, European adder, European common viper, Cross adder, Common cross adder
The Common European adder is a venomous snake that is extremely widespread and can be found throughout most of Western Europe and as far as East Asia. The color pattern of adders 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, the sexes are possible to tell apart by the color. 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. Melanistic individuals are often females.
Common European adders have a wide range. They 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. They are found further north than any other snake species. European adders live 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. They will venture into wetlands if the dry ground is available nearby and thus may be found on the banks of streams, lakes, and ponds.
Common European adders are mainly diurnal, especially in the north of their range. Further south they are known to be active in the evening, and may even be active at night during the summer months. Adders are predominantly terrestrial, although they may climb up banks and into low bushes in order to bask or search for prey. They are generally solitary and may be seen together only during hibernation and breeding season. These snakes hibernate communally in the winter. On mild winter days, they may emerge to bask where the snow has melted and will often travel across snow. Adders are not usually aggressive, tending to be rather timid and biting only when cornered or alarmed. People are generally bitten only after stepping on them or attempting to pick them up. They will usually disappear into the undergrowth at a hint of any danger but will return once all is quiet, often to the same spot. Occasionally, individual snakes will reveal their presence with a loud and sustained hissing, hoping to warn off potential aggressors. Often, these turn out to be pregnant females. When the adder is threatened, the front part of the body is drawn into an S-shape to prepare for a strike.
Common European adders are carnivores. Their diet consists mainly of small mammals, such as mice, rats, voles, and shrews, as well as lizards. Sometimes, slow worms are taken, and even weasels and moles. They feed on amphibians, such as frogs, newts, and salamanders. Birds are also reported to be consumed, especially nestlings and even eggs, for which they will climb into shrubbery and bushes. Juveniles will eat nestling mammals, small lizards, and frogs as well as worms and spiders.
Common European adders are polygynous meaning that males mate with multiple females during the breeding season. Pairs stay together for one or two days after mating. Adders usually mate in spring and females often breed once every two years. Males find females by following their scent trails, sometimes tracking them for hundreds of meters a day. If a female is found and then flees, the male follows. Courtship involves side-by-side parallel 'flowing' behavior, tongue flicking along the back and excited lashing of the tail. Males chase away their rivals and engage in combat. Often, this also starts with the aforementioned flowing behavior before culminating in the dramatic 'adder dance'. In this act, the males confront each other, raise up the front part of the body vertically, make swaying movements and attempt to push each other to the ground. Females give birth to 3-20 live young usually in August or September, but sometimes as early as July, or as late as early October. The gestation period lasts 3 to 4 months. The young are usually born encased in a transparent sac from which they must free themselves. The neonates measure 14-23 cm (5.5-9.1 in) in total length (including tail). They are born with a fully functional venom apparatus and a reserve supply of yolk within their bodies. They shed their skins for the first time within a day or two. Females do not appear to take much interest in their offspring, but the young have been observed to remain near their mothers for several days after birth. Young adders become reproductively mature at 3 to 4 years of age.
The Common European adder is not considered to be threatened, though it is protected in some countries. Reduction in habitat for a variety of reasons, fragmentation of populations in Europe due to intense agriculture practices, and collection for the pet trade or for venom extraction have been recorded as major contributing factors for its decline.
According to IUCN, the Common European adder is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List but its numbers today are decreasing.
These snakes play an important role in their ecosystem. They control the populations of species they prey on, particularly rodents, small birds, frogs, and lizards. Adders are also prey for larger mammals and birds.