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IUCN threat status:

Least Concern (LC)

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Biology

Adders are typically active during the day, when they hunt mainly for small mammals, including voles, shrews and mice. Lizards, young birds and frogs may also be taken (8). In warm conditions, adders actively hunt their prey, but they often use a 'sit and wait' technique. The adder strikes prey animals with its fangs to inject venom, it 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). Adders emerge from hibernation in March, with males emerging before females (3). For the first few weeks after emergence, they are fairly inactive and spend much of their time basking (8). After the males shed their skin in April they become more active and begin to search for mates by following scent trails. Females shed their skin a month later than males, and both sexes shed again later on in summer. Adders do not feed until after they have mated, and so during the time before mating, males and females live off fat reserves that they built up during the previous year (3). Upon discovering a receptive female, a male begins a courtship display in which he flicks his tongue 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 a 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). Female adders reproduce once every two years and are 'viviparous'; they give birth to live young which are initially encased in a membrane (7). Towards the end of August or early September, the female will return to the site of hibernation, and give birth to 3-18 young. After giving birth they 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 a yolk sac and fat reserves that they are born with. They reach sexual maturity at 3-4 years of age (3). Adders usually enter their hibernacula in September or October (3). Hibernacula are often the abandoned burrows of small mammals typically located on high, dry ground (8). A single hibernation site can contain around 100 adders (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).

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