Herefordshire Amphibian & Reptile Team

Adders

Adder
©Nigel Hand

The Adder is Britain's only venomous snake. It is a small squat species, fairly heavily bodied with a short tail and a well-defined triangular head, the female approx 55cm long and the male 50cm. One of the largest adders recorded in Herefordshire was 72cm, discovered by Dr Leighton in 1900.

The adder always has a ‘V’ or ‘X’ shaped mark behind the head and zigzag patterning down the back. Colouring varies between the sexes, the males having a pronounced black zigzag with a white or pale background coloration. Females are normally red/brown or darker with a brown background colour. This makes them very hard to see in a bank of dead bracken. The young, 15 – 20cm at birth, are generally reddish brown with a yellow tail tip. The eyes of the adder are red or coppery red with a cat-like vertical pupil. The reason for this vertical pupil is unclear as they are a typically diurnal species.

Very occasionally dark or melanistic adders, the ‘black adder’, occur locally in many parts of Britain, but are seen more in colder, mountainous areas of their distribution, especially closer to the Arctic Circle. Obviously a dark body colour will absorb more heat.

Nigel Hand's videos of adder behaviour in Herefordshire


Click to start video

Range and distribution

The Adder is absent from Ireland but present in most of Europe as far as 69’ N in Scandinavia, parts of France, Germany, northern Switzerland, Austria, across Russia and through Asia to northern China. This is the most northerly ranging snake species in the world. 

Its ability to hibernate for up to 5 months of the year and its dark melanistic coloration enable it to survive the short warm season in the very north of its range. Giving birth to live young only every 2 - 3 years is another useful adaptation. In Britain the adder is sparsely distributed throughout England, Wales and Scotland. Population numbers in the midlands are especially sparse due to high urbanization and fragmentation of suitable habitat. 

Heath land, moors, chalk down land, coastal dunes, rough commons with plenty of scrub, brambles, juniper and bracken and bracken lined field edges are typical habitat. Most habitats are situated on a sloping gradient with a south or south-easterly aspect. On flat heath land or ancient meadowland large grassy tussocks or anthills make good sunning spots for the adders.

The Adder Year

Males leave the hibernation site normally at the end of February or beginning of March, depending on the weather conditions. They shed (or slough) their skins around now and disperse toward the breeding areas and favoured basking sites ready for the arrival of the females a few weeks later.

This is the best time to observe adders as their patterning and coloration is at its peak after this first skin slough. In March/April, the males begin the ‘Dance of the adder’ where the males perform spectacular mating combat rituals. The males entwine and twist against each other with the front of their body and try to wrestle each other to the ground. The larger snake is normally the victor and goes on to mate with the female who has remained in attendance. 

Female adders appear to have a particular smell around this time, perhaps a pheromone, which the males can detect. Mating can last up to 2 hours with the male being dragged through the vegetation backwards. After mating is over the male will stay near the female for several days before departing to summer haunts. These are usually a damper site than the winter one and here they will feed. 

Adders give birth to between 3 and 10 live young. Having young tends to put great stress upon a female. Good prey years could result in more frequent births. This has only been proved in captive animals so far, but in theory this could happen in the wild. Females do not become sexually mature until 4 or 5 years of age and can live to over 10. 

Population densities in the wild are about 1 to 12 individuals per hectare, and occasionally higher in some of the good southern heath lands. Male adders will travel 0.5 – 2 km from hibernacula sites to breed and to reach summer quarters.  So plenty of habitat is essential to this species. 

The adder year ends with a return to the hibernation site ready to emerge again in late February/March the following year.

Nigel Hand's second video of adder behaviour in Herefordshire


Click to start video

Prey

Adder fangs
Adder head showing fang © Nigel Hand

Adults' prey will mainly be voles, mice, frogs, newts and lizards including slow worms. The prey is dispatched with a venomous bite, taking less than a minute to kill a lizard. The injected venom starts to digest the prey from the inside, speeding up the time when the snake may be vulnerable to attack. Adders 25cm in length are capable of swallowing a fully grown common lizard. The adder will eat between 6 and 9 vole sized meals within a year. Good vole years will mean a good adder year. 

Young adders tend not to feed until their second year as straight after birth in September they go into hibernation. They feed on small lizards and mice pups.  Captive young snakes have shown no reaction to insects, but have fed on lizards and vole viscera.

Adder bites

Belonging to the subfamily viperinae, a family ranging from Europe, Asia & Africa and closely related to the rattle snakes subfamily crotalinae, from the USA. The adder possesses 2 sophisticated fangs up to 7mm in length which when the snake strikes hinge forward, each fang having a venom gland supplying venom to the hypodermic fang. This is embedded into the victim and venom pumped in. The venom is cytotoxic, attacking the blood system and eventually the heart. 

Adders very rarely bite humans. If they do it is in defence, possibly as they are frightened of being trodden on or roughly treated. Most bites are to young males picking up adders in a show of bravado. The chances of being killed by an adder bite are very rare. There is a greater chance of being killed by a wasp or bee sting, stray dog or in a horse riding accident. Statistically one person in a decade of bites in Britain has died, and with nearly one hundred bites per year fatality must be one in a thousand bites. 70% of bites are dry bites, all bluff no venom injected. Deaths of pets or domestic animals from adders are also rare.

Adders in Folklore

Adders are surrounded in superstition even today in the 21st century. One tale I still regularly come across from countrymen who have spent their lives amongst adders is that female adders swallow their young to protect them from danger. I have also seen this in old natural history books. This most likely originated when a gravid female adder was killed with well developed young inside her. If she did attempt to swallow her own young the strong stomach acids would digest them. 

Snakes do not hypnotize their intended prey. This story was even related in Rudyard Kipling’s The Jungle Book. Snakes do appear to stare, as they have no eyelids, meaning they even have to sleep with their eyes open. 

Adders will not die till sunset if mortally wounded. More fantasy - they will take time to die if wounded, but won’t wait till sunset.

Adders and Game Birds

Gamekeepers have informed me that if an adder comes across a clutch of pheasant eggs it will eat the whole clutch. While they may occasionally take the odd ground nesting bird I have never heard of or seen an adder take eggs. The biggest threat to egg clutches is from rats, hedgehogs, corvids and foxes. Adders live mainly on rodents and lizards with also the occasional amphibian. In reality game birds do more damage to them. In the late summer they constitute a lot of reptile mortality, feeding on lizards and small snakes. The large numbers released must have an impact on the ecosystem. Anyone who keeps chicken will know how in a coop they clear the ground of vegetation and insects leaving bare earth.  More game birds appear to die on the roads than go to predators anyway. 

Conclusion

The adder has survived in our country for hundreds of years and should remain for the future. Human persecution and habitat loss are its main threats. Folklore and superstition even today have helped instil a hatred for this shy and retiring reptile, which many people have never even seen. It has a fascinating natural history and is essential to the balance of our ecosystem.

References

  1. British Snakes, Leonard G Appleby, 1975
  2. Collins Field Guide Reptiles and Amphibians of Britain and Europe, E.N. Arnold & Denys Ovenden, 2002
  3. Snakes & Lizards, Tom Langton, 1989
  4. Amphibians & Reptiles, Trevor Beebee & Richard Griffiths, 2000
  5. Habitat Management and conservation of the adder in Britain, Chris Wild & Carole Entwhistle, British Wildlife Volume 8 No. 5, June 1997
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