Vipera berus

Adders occupy one of the largest natural ranges of any venomous snake. Adders can be found from the United Kingdom to the Pacific coast of Asia. They are found as far north as the Arctic Circle and as far south as the Mediterranean Sea. ("Adder", 2005a; "Adder", 2005b; Forsman and Lindell, 1993; Reading, et al., 1996; Solway, 2005)

Adders can live in woodlands, moorlands, heathlands, and wetlands. Open, sunny glades and/or slopes suitable for sunning are important components of preferred habitats. It is also crucial that there is relatively dense ground cover available for adders to find shelter. Adders can survive in cold grasslands found in the northernmost areas of its range. ("Adder", 2005a; "Adder", 2005b; Reading, et al., 1996)

Adders begin life approximately 16-18 cm long and can grow as long as 80 cm. The mass of male adders generally ranges from 50 to 70 grams, while the mass of females ranges from 80 to 100 grams. Mature adders may be a variety of colors. In general, male adders are grey, cream, whitish, or pale-yellow, with a distinct dark pattern on their backs and sides. This pattern can be described as zig-zag or a series of contiguous “X”s. The sides of Vipera berus often have a broken zig-zag pattern. Adders have a distinctive superorbital scale pattern, the scales extend over their eyes, giving them a lidded appearance. Vipera berus has a recognizable dark colored “V” on its head, the point of which can be found between its eyes. Female adders have the same distinct patterns along their backs and heads, but their coloring is slightly different. Females are usually reddish in color with brown-toned markings. Juvenile adders are also generally reddish. Occasionally, adders can be completely melanistic. ("Adder", 2005a; "Wild Woods Adder", 2005; "Adder", 2005b; Solway, 2005; "Adder (Vipera berus)", 2004)

Adders, like other members of Viperidae, have hinged fangs used to inject venom into their prey. Hinged fangs fold at the base to lie against the roof of the mouth. This feature enables these fangs to grow quite large in comparison to those belonging to snakes without hinged fangs. ("Wild Woods Adder", 2005; "Adder", 2005b; Solway, 2005; "Adder (Vipera berus)", 2004)

Adders are viviparous. Adder eggs are fertilized internally during copulation. ("Vipera berus - Adder", 2005; Solway, 2005; "Adder (Vipera berus)", 2004)

Adders mate seasonally in the spring, usually April, soon after emerging from hibernation. The males emerge first and stay close to the hibernation site in an area referred to as the mating ground. As females emerge, males swarm around them and allow females to choose a mate with whom to copulate. Male adders can also locate sexually receptive females using their keen sense of smell. After locating a receptive mate, copulation occurs. Males generally remain with the female for several hours after mating. During this time, the male will fight any other males who attempt to court his mate. When two adders fight, both raise their bodies into the air and intertwine themselves in an attempt to wrestle one another to the ground. This method of fighting is known as the "dance of the adders". After several hours of remaining with his mate, the male leaves to find another mate. (Ernst and Zug, 1996; "Adder (Vipera berus)", 2004)

There are several notable courtship rituals that occur before mating between a male and female. These rituals include tongue flicking, tail vibrations, and body quivering. When two males try to court the same female, fighting can occur during which males raise the upper half of their bodies off the ground and attempt to wrestle each other to the ground. More than two males can be involved in these fights. (Ernst and Zug, 1996; "Adder (Vipera berus)", 2004)

April is the most common month during which adders reproduce. Their gestation period ranges from three to four months, so young live adders are born during the fall months, generally during hibernation. Female adders usually give birth to approximately 12 live young. Three to four years following birth, these young adders will be ready to mate with other adders. ("Adder", 2005b; Ernst and Zug, 1996; "Adder (Vipera berus)", 2004)

The gestation period is approximately 3 to 4 months. Young adders are often born slightly before or during hibernation in those populations that hibernate. The young are born with fat reserves to aid them in survival until the end of hibernation. They also have access to a yolk sac, which is full of nutrients necessary for survival. At birth, Vipera berus individuals measure approximately 16 to 18 cm long. Young adders will not become sexually mature for 3 to 4 years.

It is not well known how long young Vipera berus remain with their mothers. The offspring of other species of viviparous vipers have been known to remain with the mother for several hours after birth before dispersing. Young vipers are independent soon after birth. (Ernst and Zug, 1996)

Adders have a fairly long lifespan. They generally live for 10 to 15 years in the wild. There are reports that claim adders have reached 25 years of age. Little information is available describing the lifespans of captive adders. This may stem from the fact that adders are neither desirable as pets, nor particularly endangered, thus few are kept in captivity. ("Vipera berus - Adder", 2005; "Wild Woods Adder", 2005)

Adders are solitary animals. They rarely are found with other adders, with the exception of mating and hibernation. Adders are most active during the hours surrounding sundown. During this time of day adders can be found actively hunting. Adders are motile creatures that move by slithering along the ground. Adders usually begin hibernation during either September of October. They hibernate communally in pre-existing underground areas, or hibernacula, such as abandoned mammal burrows, crayfish burrows, or tortoise burrows. One hibernaculum can house up to 100 hibernating adders. Generally, only adders living in colder habitats hibernate. As the temperature drops, adders will move deeper into the hibernaculum to reach depths where the temperature does not drop below freezing. It is not uncommon for adders living in mild climates to remain active all year round. ("Adder", 2005b; Ernst and Zug, 1996; Solway, 2005; "Adder (Vipera berus)", 2004)

Very little is known about the home range of Vipera berus. (Solway, 2005)

There are several important senses utilized by Vipera berus in perceiving the environment and communicating between individuals. Adders have well-developed eyesight, which is valuable for hunting as well as general perception of the surrounding environment. In addition to sight, adders can hear, although they lack an outer ear. Instead, they detect sound through a mechanism called "skin-muscle-bone" route. Sound waves hit the skin of the adder and the vibrations are transfered through the jaw muscles and the several bones until they reach the snake's inner ear. Adders also have a well-developed sense of smell. They smell using both the tongue and nostrils. As Vipera berus flicks its tongue in and out of its mouth, the tongue is actually picking up tiny particles and molecules and transfering these to small openings on the roof of its mouth which lead to the olfactory center where the particulate matter will be identified as having a specific smell. These highly-developed senses combine to make Vipera berus individuals very effective predators. (Ernst and Zug, 1996; Solway, 2005; "Adder (Vipera berus)", 2004)

Communication between adders is very important during mating season. The sense of smell plays an especially important role in mating, particularly in finding an appropriate mate. In general, snakes emit pheromones that can be sensed by other snakes. Pheromones are key chemical indicators in reproduction. Pheromones can indicate whether a female is sexually ready to reproduce. Pheromones can linger in the air long after a snake has occupied a given area, which further aids in communication between individuals over longer distances. As pheromones are chemical indicators, snakes sense pheromones using chemical receptors such as taste and/or smell. (Ernst and Zug, 1996; Solway, 2005; "Adder (Vipera berus)", 2004)

Adders are carnivorous and consume a variety of prey, including small mammals such as voles (Arvicolinae), shrews (Soricidae), and mice (Murinae), as well as small lizards, birds, and frogs. There are two predatory techniques generally utilized by Vipera berus. The first is called the “sit and wait”, or ambush, technique. Adders wait in one place for prey to pass by so they can strike out, using fangs to inject their prey with enough venom to be fatal. Their keen sense of smell is then used to follow the wounded animal to its death where Vipera berus will proceed to consume the animal head first. The second technique involves actively seeking out prey. Adders generally use this technique when they are most active. Being a crepuscular creature these hours are usually right around dusk. ("Adder", 2005a; "Vipera berus - Adder", 2005; Forsman and Lindell, 1993; "Adder (Vipera berus)", 2004)

There are several major predators that may prey on Vipera berus, both vertebrates and invertebrates. The most prominent vertebrate predators include foxes, Eurasian badgers, large diurnal birds of prey, and owls. Adders can also be preyed upon by larger snakes. Adders are cryptically colored, which protects them from many predators, and they can defend themselves with their venomous bites. ("Vipera berus - Adder", 2005; Ernst and Zug, 1996; "Vipera berus - Adder", 2005; Ernst and Zug, 1996)

One of the important roles played by Vipera berus is controlling the populations of small mammals, particularly rodents. Adders also contribute to the control of small bird, frog, and lizard populations. In addition, adders provide a source of food for larger mammals and birds. ("Vipera berus - Adder", 2005; Ernst and Zug, 1996)

Adders play a key role in controlling populations of rodents and other small animals that are sometimes considered pests. Adders can also be milked to collect their venom, which can then be used to produce anti-venom for the treatment of adder bites. ("Adder", 2005a; "Adder", 2005b)

Adders are venomous snakes and their bites are dangerous to humans. While adder bites are rarely fatal, they do require immediate medical treatment and are very painful. Adders can kill small animals like dogs and cats if they feel threatened. Pets should therefore be closely watched in areas where adders occur. ("Vipera berus - Adder", 2005; "Adder", 2005a; "Vipera berus - Adder", 2005; "Adder", 2005b; Russell, 1983; Solway, 2005)

Adders are a protected species in some countries, Britain being one example. Their reputation as venomous has been quite detrimental to conservation efforts. People have been inclined to kill adders regardless of their conservation status because of their fear of these animals. Adders also suffer from loss of habitat, mostly due to human activities such as development and agriculture. Deforestation and scrub encroachment on preferred habitats also negatively impacts adders. ("Adder", 2005a; "Adder", 2005b; "Adder (Vipera berus)", 2004)

There are many species of snake both closely and distantly related to Vipera berus whose common names may contain the term "adder". Vipera berus is the only species whose actual common name is "adder". Vipera berus is also sometimes referred to as the common viper. The common name "adder" is often given to venomous vipers (Viperidae) throughout the Old World. Several examples of other "adders" are: rhombic night adder, Causus rhombeatus, puff adder, Bitis arietans, and death adder, Acanthophis antarcticus. ("Venomous Snakes of Liberia and West Africa", 2005; Russell, 1983; Solway, 2005)