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
amongst a bank side 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 player, then click play button
to see video Video 2
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
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.
Current
biodiversity action plans seem to omit the adder possibly afraid
of the bad publicity of backing a venomous creature.
Building and habitat loss are making translocation an only
alternative, but habitat at the new sites must be suitable.
Adders need large tracts of land including hibernacula, summer
quarters and abundant prey if they are to prosper. More
legislative protection and better education of the general public
is the way ahead. It may not be a loveable furry animal with
human attributes, but it has a fascinating natural history and is
essential to the balance of our ecosystem.
References
British Snakes
Leonard G
Appleby 1975
Collins Field Guide Reptiles and
Amphibians of
Britain and Europe
E.N.
Arnold & Denys Ovenden 2002
Snakes & Lizards Tom
Langton 1989
Amphibians & Reptiles
Trevor Beebee & Richard Griffiths 2000
Habitat Management and
conservation of the adder in Britain
Chris Wild & Carole
Entwhistle British Wildlife
Volume 8 No. 5 June 1997
