The adder is typically active during the day, when it hunts mainly for small mammals, including voles, shrews and mice. Grasshoppers and locusts, lizards, young birds and frogs may also be taken (8). In warm conditions, the adder will actively hunt its prey, but it often uses a ‘sit and wait’ technique. The adder strikes prey animals with its fangs to inject venom, then releases the prey and follows the scent trail it leaves behind. Upon finding the dying or already dead animal, the adder begins to swallow it head first (3).
The adder emerges from hibernation in March, with males emerging before females (3). For the first few weeks after emergence, this species remains fairly inactive and spends much of its time basking (8). After the male has shed its skin in April it becomes more active, and will begin to search for potential mates by following scent trails. The female sheds its skin a month later than the male, and both sexes shed again later on in summer. The adder does not feed until after it has mated, and so during the time before mating, both the male and female adder live off fat reserves that are built up during the previous year (3).
Upon discovering a receptive female, the male begins a courtship display in which the tongue is flicked over the female’s body. The male and female may vibrate their tails briefly and bouts of body quivering may ensue. If the courtship is a success, copulation takes place, after which the pair may remain together for two hours or so. If another male approaches the pair at any point, the first male will defend the female aggressively, and a fight may result (3). These fights are known as ‘the dance of the adders’ as the males partly raise their bodies off the ground and may become entwined, often repeatedly falling to the ground and rising up again. More than two males may be involved in such a contest (4).
The female adder usually reproduces once every two years, returning to the site of hibernation towards the end of August or early September to give birth. The adder is viviparous, giving birth to between 3 and 18 live young which are initially encased in a membrane (7). After giving birth the female must feed intensively in order to build up sufficient reserves for hibernation (3). The young adders do not feed until the following year, but live off the yolk sac and fat reserves that they are born with. The adder reaches sexual maturity at three to four years of age (3).
The adder usually enters its hibernacula in September or October (3). Hibernacula are often the abandoned burrows of small mammals typically located on high, dry ground or the overgrown root systems of fallen trees. The adder usually uses the same hibernation site for life (9).
Although adders are poisonous, they are not aggressive and rarely bite humans or domestic animals, preferring to retreat into thick vegetation instead. Most adder bite incidents result when they are picked up or trodden upon, and in most cases they are not serious. The elderly, the very young or people in ill health are at most risk (3).