The viviparous lizard, more often simply referred to as the common lizard, belongs to a large family of lizards known as the Lacertids, containing approximately 250 species worldwide. Remarkably it is the only member of the entire family that is viviparous, (or more correctly, ovoviviparous), giving birth to live, fully developed young; all the others lay eggs.
Even more remarkably, populations of this same species living in the Pyrenees, at the far south of their range, are not live bearers at all, but like the rest of the species in the family they too lay eggs! Here in Britain, however, the species lives up to its name, Zootoca vivipara, both parts of which refer to its live-bearing mode of reproduction.
The viviparous lizard is a small lizard reaching lengths of about 12-14cm, of which approximately 60% is tail. The colour and markings are extremely variable, although most individuals are some shade of brown or pale green with a complex pattern of stripes running the length of the body. These usually take the form of a dark vertebral stripe which may be complete or broken up into a ‘dotted line’, together with parallel stripes down either side, often comprised of dark or light spots varying from bold to indistinct. As a rule the stripes are generally more pronounced in the females, while the spots are better defined in the males. The undersides of the males are orange or red, speckled with dark flecks, while those of the females are uniform pale yellow or peach with few, if any, dark markings. Completely black, or melanistic, specimens can be found from time to time.
Occasionally, the males may appear bright emerald green, potentially causing confusion with another British lizard, the sand lizard. However, no such confusion should occur in Somerset where sand lizards do not exist. In common with many other lizards, it would appear that the colour of viviparous lizards may vary under different circumstances, as the intensity of green can rapidly fade when the animals are captured and handled.
When first born, the young are about 4 cm long and are very dark brown or black, although within a few weeks the colour lightens to a paler bronze and their markings begin to appear.
Viviparous lizards are usually found in unmanaged, or lightly managed, undisturbed places, generally preferring open country that provides cover but also plentiful basking opportunities. Their habitat preferences are wide and they can be found on heathland, commons, scrubby hillsides, cliffs, road or railway embankments, woodland edges, hedgerows, banks, derelict land or abandoned quarries. They are found predominantly on dry, well drained soils but may be equally at home in bogs and marshes.
The viviparous lizard is unusually cold-tolerant and on the continent it ranges further north than any other species of lizard, being found well within the Arctic Circle. This tolerance means the viviparous lizard is often the first reptile to be seen in the spring; with males sometimes emerging from hibernation in February, while females will not emerge until several weeks later, usually around mid-March.
This is a very alert, fast and nimble creature, disappearing like a flash at the first hint of any danger. However, if disturbed while basking they will often re-emerge within a few minutes, so patience may be rewarded when watching these creatures. They spend much of their time basking, particularly in the morning when temperatures are low, and often utilise a feature in the landscape, such as a tree stump, fence post or anthill as a favoured basking site. During the breeding season they may defend their basking sites from intruders, yet at other times they can be surprisingly gregarious often basking in groups, each lizard flattening and angling its body to expose the maximum surface area to the sun.
From these favoured basking sites they have little circuits that they regularly patrol in search of prey which consists of a wide range of insects and soft bodied invertebrates. Favoured food items include small beetles, grasshoppers, spiders, harvestmen, flies and caterpillars, although they tend to avoid the very hairy species of caterpillars. They will lick early morning dew from the ends of grass blades.
Mating occurs during April when the males may become quite quarrelsome. Females appear to initiate the courtship, seeking out the males who then seize the female in their jaws, either behind the head or by a flank, before inserting a hemipene into her cloaca. Mating may last up to half an hour.
The females become increasingly conspicuous as summer progresses and they become heavily gravid, spending more time basking. In July or August they give birth to an average of 5-8 young, each born enclosed in an egg membrane which they quickly rupture to emerge as fully developed miniatures. At this time the populations increase appreciably, boosted by large numbers of juveniles. However mortality during the first hibernation would appear to be high as comparable numbers of juveniles never seem to reappear in the subsequent spring. Within just a couple of days of birth the young slough their first skin and begin to feed. Sloughing in lizards is done piecemeal, the skin breaking up into fragments as it peels away, unlike snakes in which the skin is sloughed in one piece. Growth of young lizards is rapid, males reaching sexual maturity on emergence from their second hibernation and females on emergence from their third.
Together with the slow worm, the viviparous lizard is capable of autotomy, the shedding of the tail to escape from predators. The fracture occurs along predetermined autotomy planes situated across selected vertebrae within the tail. When the tail is discarded it begins to twitch vigorously distracting predators from the escaping lizard. A new tail will eventually grow to replace the discarded one, however the process is slow and replacement tails are easily recognisable, never being quite the same as the original. A new tail will contain a cartilaginous rod rather than fully formed, ossified vertebrae, therefore there are no replacement autotomy planes and a replacement tail can only be shed a second time if an autotomy plane still exists anterior to the original break.
Viviparous lizards are widespread across northern and central Europe from arctic Scandinavia south to northern Spain and northern Italy. They are not found in the Mediterranean basin, where conditions are too hot for them, although they are present at high altitude in the central Balkans as far south as Macedonia. Their range extends eastwards across Russia and northern Asia as far as the Pacific coast and Sakhalin island.
They are widespread throughout Britain, and are the only species of lizard found in Ireland.
William Baker in 1851 declared the species common in many parts of Somerset and described watching them basking on dry hedgerow banks around Bridgwater as well as on the Quantocks and Mendips.
Likewise, Charbonnier, both in an article for the Proceedings of the Bristol Naturalists Society in 1887, and again in correspondence to Gerald Leighton in 1903 describes the species as fairly common on Leigh Down and Brockley Common, in North Somerset. Herbert Balch also corresponded with Leighton, stating that common lizards ‘abound in Somerset’, although his assertion that sand lizards are found on the Mendips is incorrect and undoubtedly refers to this species.
In 1974 John Burton writing in the Annual Report of the Somerset Trust for Nature Conservation suggests that apart from the inevitable destruction of some of their habitats through human activities of one kind or another, the abundance of viviparous lizards in Somerset does not appear to have changed very much since the time of Baker and Charbonnier, and he sees no need for any special measures for their conservation in the county.
Today viviparous lizards remain widespread across the county but I would not assert that they are common or that they ‘abound in Somerset’; in fact they are generally rather uncommon, and highly localised, although they can be quite abundant on some of the sites where they do occur. They are significantly more common in the west of the county than the east. Burton’s comment about the inevitable destruction of some of their habitats is curious as it fits with a general perception of a low intensity pattern of decline and it seems likely that viviparous lizards would once have been more widespread in Somerset than they are now, intensification of farming and development having pushed them to the margins.
Their strongholds in the county are the upland heaths and moors of Exmoor and the Brendons, the Quantocks, the Blackdowns and the Mendips, where they often live sympatrically with adders. It is unusual to find an adder site where there are not also lizards, although their habitat preferences are wider than those of adders, so the opposite is not true.
Away from these strongholds there are various small populations scattered across the county, predominantly on reserves or other protected sites. The species is rare both in and around urban areas and on farmland, although where linear features such as railway embankments or canals penetrate these habitats lizards may follow them in.
Lizards are found on several lowland sites in the Vale of Taunton as well as on the peat moors and along the river Parrett around Bridgwater. However, the recent rapid expansion of Bridgwater has displaced several populations of viviparous lizards, perhaps from sites where Baker once watched them basking on the hedgerow banks.
In North Somerset the species is present in the Gordano Valley and there is a significant population on the calcareous grassland of Walton Common overlooking the Valley.