Adder (Vipera berus): Timid reptile with a bite.
EVEN THE GREAT NATURAL HISTORIANS OF THE PAST get it wrong sometimes, even the famed Gilbert White, so let me start by exploding a myth relating to the adder straight away: they don't -- and probably never have in their long existence on Earth -- swallow their young in an undertaking to protect them from danger. It is quite easy to comprehend how naturalists of yesteryear made this fundamental error -- crocodiles, caiman and alligators manoeuvre their offspring to safety by means of oral transportation -- through a number of animal behaviours discovered during field observations that would have strongly influenced their theories. White, for instance, in his much admired 'The Natural History of Selbourne', noted on cutting open a female adder after she had been basking in a grassy spot, "There was little room to suppose that this brood had even been in the open air before... because then probably we should have found them in the neck, and not in the abdomen." The female had been carrying fifteen young snakes on this occasion, and since adders give birth to live young, it is obvious where White and many other field naturalists of the time came to make such an incorrect observation. The modern scientific family name of Viperidae is supposedly derived from the Latin 'vivus' and 'paro' -- viviparous -- meaning to bare live young, although there are many snakes of the viper family that lay eggs rather than young serpents.
Another myth of folklore: the miniature reptilians do not hide under the belly of their mother when threatened. The simplest explanation for the notion that the young are protected by hiding under the adult's belly must be derived from the habit of the infant snakes, immediately after birth, taking-up the same favoured sunbathing spots as the adults, even lying on top of them at times to soak up as much warmth as possible. However, it is equally as likely that the adult snake will reverse the favour, giving rise to the mistaken notion of overbearing maternal protection. Indeed, White also noted that the neonates are "issued into the World with the true viper spirit about them," suggesting that parental protection is not required, and fortunately so, for the female has no further interaction with her offspring once they are born. An internal yoke sac keeps the young animals alive just long enough for them to find their bearings in the wider world, before heading out into the heath and scrubland in search of a first meal.
The adders of Norfolk's heathlands are at the western edge of their global range, one that extends across Europe, touches Mongolia and northern China, delves into Russia, southern Siberia and the Arctic Circle (up to 67°N), eventually culminating on Sakhalin Island, just north of Japan, comfortably commanding the largest known terrestrial range of all snakes: a remarkable achievement for any animal, particularly so for a reptile. Justifiably, you might be wondering how an ectothermic (cold-blooded) creature -- requiring an internal body temperature of 30°C to be fully operational -- can get by in such extreme environments where wintertime temperatures can render them completely immobile and cause certain death? The answer to this precarious conundrum lies in the rays of the sun, which are of vital importance to the adder, providing them with the body heat they need to get about, to find food or a mate and to flee danger. The warmth of the sun helps males develop sperm and gravid females to speed up the growth of their unborn young. It is the adder's ability to absorb summertime heat that facilitates their success over such a vast global range; but when the heat runs out, they must shut-up-shop, they must hibernate.
Using old rabbit burrows, mouse holes and deep crevices located within the root systems of old trees, Norfolk's adders will leave the openness of the heath for the confines of their subterranean winter accommodation once the cooler days of autumn have commenced. In this hibernaculum they will share space with other adders, grass snakes, toads and lizards, all seeking shelter from the lethally cold conditions exhibiting on the land above them. Here they will stay, putting their body-clocks into slow-motion until the springtime. It is not until late February -- on a particularly warm day -- or early March before they rise from their 5 - 6 month shut-down, and during this time it is possible to observe their most interesting behaviours at close quarters. Whilst kneeling down next to an hibernacula well known to me -- many days before the Spring Equinox -- I've watched in near disbelief as adders emerged from their wintertime confines in a state of juddering rigidness, barely capable of moving across the frost covered lichens and birch leaves, suffering the apparent numbness of body that must be likened to human fingers of the most paralysed kind, frigid with cold and pain, and utterly useless to their owner. For the following few weeks the snakes -- all male at this point in time, the females appearing some weeks later -- will bask at every opportunity, soaking up the milky rays of early season sunshine, renewing their brio in anticipation of reproduction.
Flattening their bodies by opening the rib cage to expose maximum body mass to the sun, adders can appear almost trodden upon, such is the apparent spread of their girth. Unlike mammals, however, the snakes cannot regulate their body heat internally (homeostasis). Instead, they prevent themselves from overheating by either changing body position, to the extreme extent of coiling up into a ball as tight as a clenched fist, or moving into partial shade under nearby vegetation -- either method produces the desired effect of reducing the relative exposure of scaly body mass to the sun's warmth. On the coolest days, it's possible to observe a solid clump of male adders basking together outside their wintering quarters, a partially intertwined mass containing eight snakes or more, each using the limited body heat of his congener to retain as much warmth as possible. I've read that adders will contentedly remain basking during gentle precipitation (even drinking water droplets from their scales), although I haven't witnessed this myself, but I can confirm that hail and sleet are not to their liking, sending them back into the shelter of their underground chambers until the inclement bombarding has ceased. Incredibly, whilst underground, it is understood that they can determine when weather conditions are clear enough to resume their sun worship by detecting the vibrations of hail and rain through their lower jaw bone, the oscillations of which are subsequently relayed to the inner ear for Enigma-style processing.
ALL OF THIS LAZING ABOUT IN THE SUNSHINE is a mere preamble to the more important matters of procreation, but first the increasingly amorous male must spruce himself up, look dapper and don his most splendid bib and tucker -- not by wearing more, but by wearing less. Sloughing (pronounced sluffing) is the act of shedding old skin, which, in the case of adders, becomes dull and worn after a full year's worth of use on the heath and needs to be replaced. Easier said than done for a snake you might think, but they've perfected a method of skin removal that is as simple as it is clever. Firstly they produce a secretion, a type of loosening agent that lifts the old unwanted skin away from the clean layer beneath, giving the reptile a milky, opaque appearance, particularly around the eye (snakes have no eyelid, instead a transparent scale called the spectacle sits over the optic). Once loosened and beginning to fray, the adder will deliberately snag the corner of its mouth on spiky vegetation, prompting the skin to separate from the animals head and peel off backwards along the snake's body as the reptile moves forwards. After half-an-hour or so, a perfectly formed, transparent, inside-out husk is left hanging from the heather or gorse, discarded by the serpent in the manner a country gentleman would divest himself of his long stockings after a day in the field.
It is now that the little male snakes (normally up to 60cm long) look their most resplendent, sporting a bright green and black livery with a satin-like, pruinose effect: sea green to oyster grey is in stark contrast with the charcoal hued, diamond shaped wedges that decorate the adder's spine as they sparkle against the drab, vapid bracken and gorse. Freshly attired, their activities increase tenfold as they gently crunch and rustle circuits through the brittle undergrowth, forked-tongues flicking eagerly in search of the most valued catch -- a receptive female. Emerging several weeks later than the males, the noticeably larger females release pheromones that waft across the heathland and prove irresistible to their potential suitors, who make great speed towards their temptress. Once united, it is not all plain-sailing, as more than one beau may be drawn to their serpent-siren, provoking behaviour rarely witnessed and most obscurely named: the dance of the adder.
This is no foxtrot or tango, no salsa or waltz, just a plain and simple arm-wrestle, a show of bravado and brawn: a contest. Should our combatants be of near equal size --squaring-up as red deer stags do during the rut -- they will engage, wrapping their brightly coloured bodies around each other, striving to attain leverage over the other, endeavouring to push his opponent into the ground, and keep him there until exhaustion causes the vanquished to retreat, at pace, into the open country of the heath. At no point during this contest do the adders use their venom as a weapon against each other, perhaps because they are immune, or perhaps it's a gentleman's agreement, Queensbury rules, no biting below the ventral scales... The winner wins the right to court his quarry, a graceful and seductive affair with the male trembling and jerking his body over the female, tongue flicking, tail quivering as he slowly wears down her defences and mates, a wooing that can last for several hours. Then they will go their separate ways, the male to secure another female, and the dam to generate her young.
ONCE THE MONTH OF MAY IS THROUGH the adders will become scarcer, abandoning their hibernation and breeding locals in favour of damper, grassier terrain lower down on the heath, where they will find sustenance in the form of field voles, mice, small rats and occasionally amphibians. It is now that an astonishing sensory system is deployed. Their perpetually flicking, forked tongue collects particles from the air, transferring them into a small aperture located in the roof of the mouth called the Jacobsen's organ. Here the chemicals within the gathered particles are analysed, interoperated and translated into useful information: friend or foe; chase or hide; mouse or frog. Vipers are generally ambush predators, their powerful and muscular bodies providing great speed in attack, with adders working in a similar fashion, locating areas where prey is abundant, and waiting. Should a potential victim come within range, the adder will strike at fulgurous speed, and then wait once more. The venom, a toxic concoction of enzymes -- mostly proteinase in viper venom, causing severe tissue trauma -- is injected through hollow, hinged hypodermic fangs that are connected to venom glands sequestered under the eye sockets, and propelled with a rapid muscular contraction into their prey's punctured body, causing imminent, if not instant mortality. Should the stricken animal be capable of escape, the adder will find it, following the trail of scent left by the creature, and then the adder will once again wait, until its victim is fully disfunctional. Upon locating the dead animal, the adder will disconnect its lower jaw and walk the dead carcass down its throat -- head first and whole -- using muscular contraction, realigning the jaw bone with the aid of ligaments possessing bungee cord qualities through bouts of exaggerated gaping and yawning. Powerful digestive juices and a lengthy spree of sunbathing complete the feast, something that only needs to be implemented 5 - 10 times a year; such is the efficiency of the reptilian's ectothermic lifestyle.
Observing adders in the field is an extremely rewarding experience, should you have the tenacity to wait around for the action to happen. Locating the snakes is no easy task for the untrained eye however, even when in the perfect location. The patterning of the skin morphs remarkably well with the shadow and light created by dead bracken, yet this broken foliage is also the giveaway clue: there's a strong link between adders and bracken, their hibernacula often located where the plant is abundant, with the thick, matted layers of dead material providing both aboveground insulation and a perfect platform to bask upon. If you are fortunate enough to find the animal, keep your distance and do not attempt to pick them up or disturb them, rather enjoy the knowledge that you're observing one of the Natural World's most sophisticated innovations only a few miles from where you live.
Female adders are only capable of bearing young once every 2 - 3 years; such is the stress of pregnancy and parturition. They do not eat during this time and can be near to atrophy once the cycle is over. It's also worth noting that they do not normally breed until 8-years of age or reaching 20-inches in length, when they will produce 6 - 12 live young, the sexes of which are equally divided between males and females. It is no wonder that they need to live for 30-years or more.
So how can an ectothermic creature, that requires an internal body temperature of 30°C... get by in such extreme environments where wintertime temperatures can render them completely immobile and cause certain death?
With its scales glinting in the early spring light, an adder soaks up every last drop of warmth offered by the setting sun. The snake's appearance will brighten once the layer of old skin that's lasted throughout a winter's hibernation has been sloughed.
Hidden amongst dried gorse and bracken as it peers out at the golden spring sunshine, this male viper gently warms it body during early March. After mating, it will be heading off towards valley mire where it will feed for the first time in months.
Coiling tightly amongst dried birch leaves and the lichen Cladonia fimbriata, this adder is reducing its exposure to the warming sunshine by lessening relative body mass made available to absorb the electromagnetic radiation of the brightest star, thereby avoiding the risk of overheating.
Resembling a tortured soul from a Gothic novel, the shed skin of an adder recently emerged from hibernation rests amongst stems of heather. It can take several hours to remove the unwanted layer, leaving the snake vulnerable to predators.