The slow-worm - Anguis fragilis, or blind-worm as it is sometimes called, is a legless lizard. It is certainly not blind and it is not always slow, but can be rather slow and deliberate when stalking prey. Rather, its name comes from the Old English slá-wyrm meaning 'slay worm1' and refers to the fact that it will feed upon worms.
Often found in gardens, the slow-worm eats large quantities of slugs which are its principal food. For this reason it is often referred to as the 'gardeners' friend' and should therefore be valued by farmers and gardeners.
Slow-worms belong to the class Reptilia, which also includes:
- Lizards and snakes - Order Squamata
- Turtles and tortoises - Order Chelonia
- Crocodiles and alligators - Order Crocodilia
- New Zealand tuatara - Order Rhynchocephalia
These represent only four of the 16 orders known to have flourished during the Mesozoic era, the so-called Age of Reptiles, when these were the dominant animals.
Adaptations of Reptiles
Reptiles are the first group of vertebrates adapted for life in dry places on land. They have dry horny skin and scales to prevent loss of moisture from the body and to facilitate living on rough surfaces. The class name refers to the mode of travel (L. reptum - to creep).
The study of reptiles is called herpetology (Gr. herpeton - reptile).
The reptiles show advances over the amphibians in having:
A dry scaly body covering adapted to life away from water.
Limbs suited for rapid locomotion.
Further separation of oxygenated and deoxygenated blood in the heart.
Complete ossification of the skeleton.
Eggs suitable for development on land with membranes and shells to protect the embryo.
Reptiles lack the insulated body covering, regulated body temperature, and some other features of birds and mammals.
During the course of evolution the slow-worm, like other legless lizards, changed its habits and so, instead of living above ground, burrowed into it. To facilitate this the bodies of the legless lizards became streamlined and their legs receded.
Description of the Slow-worm
Slow-worms are always shiny. The colour of slow-worms is variable and they can be brown, bronze or greyish. Usually the males are greyish and the females are brown or bronze with a dark stripe running down their backs. There is also a blue spotted variety, this being more common in coastal locations, and does not usually occur until an animal is at least three years old.
Being legless they do look rather snake-like, but are distinguished from their close relatives, the snakes, by a fold of skin running along each side of the body, and by the fact that they have eyelids. The slow-worm also has a black forked tongue, which it flicks in and out of its mouth and uses as a feeler.
Due to its snake-like appearance and forked tongue (sometimes referred to as a 'sting'), the slow-worm is often mistaken for an adder and slaughtered. However, it is perfectly harmless and quite safe to handle.
Slow-worms live mostly in heaths and open woods, and are frequently found beneath rocks and stones. They are frequently found in domestic gardens where they will often be found at the top of compost heaps or underneath carpet, corrugated iron or slate. Provision of these natural radiators, or even black plastic, will do much to encourage slow-worms in the garden. Due to their secretive nature, little is known about the life history, habits and ecology of slow-worms.
In order to encourage slow-worms in the garden it is a good idea to leave some untidy corners or an overgrown rockery. Slow-worms also need a place with light, loose, well-drained soil where they can burrow. They use the underground burrow to rear young and hibernate in winter. Embanked hedges are good places for their burrows.
Slow-worms feed on invertebrates, such as slugs, snails and worms and catch them in the mouth. They use the tongue to 'taste' the air and detect their prey. The grey slugs, which attack the gardener's lettuces, are particularly liked. Compost heaps attract a lot of worms - which is a reason why slow-worms are often found there. They also eat hairless caterpillars and other grubs.
Snails are a vital source of calcium for the breeding female slow-worm.
As slow-worms hunt at night, it is difficult to observe them feeding.
Mating occurs in late April or May, and there is often rivalry between males for a particular female. Some old males bear permanent battle-scars on their bodies. The successful male grabs a female by the neck during a long mating ritual.
After mating, the female incubates the fertilised eggs inside her body. Each young slow-worm develops inside an egg sac, which breaks when the mother gives birth in August/September. During the summer she lies in the sun to help the developing eggs grow. This way of looking after the eggs is called ovo-viviparous, because the young emerge from their mother inside their egg sac.
Reptiles in hot countries lay eggs and incubate them outside the mother's body - often in hot sand.
The young slow-worms develop inside their mother's body during the summer - each one in a separate egg sac. They are born in August or September, the litter size ranging from six to twelve. After birth they are able to fend for themselves immediately, even though they are only 5cm long when newborn.
When born they are a beautiful pale gold colour, but this becomes duller as growth proceeds. As they grow, they shed their outer skin, which peels off.
An adult usually grows to about 30cm in length but can reach lengths of up to 50cm.
The slow-worm is possibly the longest-lived lizard in the world. Records show that they can live up to 30 years in the wild, and they have been known to survive to 54 years in captivity2).
Predators and Other Threats
Slow-worms are eaten by birds (eg, buzzards, and some people think, even pheasants), but cats also catch a lot and, although they probably don't eat them, they can unfortunately maul them to death.
Slow-worms, like the other two of Britain's native lizards, the common lizard and the sand-lizard, are able to shed their tails at will. This is because the tail vertebrae are completely ossified at their centres and if the tail is seized, the vertebrae separate at one of these 'breaking points'. This process is known as autonomy, and enables the lizard to escape if seized by a predator. The predator is left holding only the tail end. The lizard is able to regrow its tail in time but, unfortunately, the new tail never achieves its original length.
The slow-worm is common in Great Britain but is naturally absent from Ireland (those found there, in the area of the Burren, are thought to have been introduced).
In Britain, slow-worms can be found as far north as the Hebrides. The most recent UK distribution maps seems to show that the slow-worm, although widespread across the UK, is more common in the south and becomes scarcer in the north and west of the county.
Slow-worms are not found further north than 60° of latitude, but extend southwards through Europe to North Africa and western Asia. There are 40 species of slow-worm worldwide. However, there is only one other species of slow-worm in Europe, which is the glass-lizard (Ophisaurus)3.
The Slow-worm is protected from being 'sold or killed or injured' under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended). The species was included in the schedule due to its decline in the UK.
It is an offence to kill any British reptile species (snakes or lizards).