The slow worm

David Chapman / 29 August 2012

They aren’t always slow - and they certainly aren’t worms - but slow worms are the most commonly-seen reptile in British gardens.

The slow worm is actually a lizard, though this lizard has lost its legs through evolution, obviously finding legs to be a hindrance to its lifestyle - probably while trying to hide in holes and compact vegetation.  Without legs, the slow worm cannot accelerate quickly and in cold weather it is inclined towards lethargy, but its long muscular body can wriggle quite vigorously.

Since slow worms lack legs they are more likely to be confused with a snake than a lizard but their smaller size and markings should be enough to distinguish them. Sexing a slow worm is also fairly straightforward.  Males (seen in the photo) vary in colour between silvery-grey and copper, but are always predominantly of one colour, whereas females are a bronze colour with dark flanks, belly and vertebral stripe. 

There are several biological differences which make the slow worm a lizard rather than a snake.  Unlike snakes, lizards have: a moveable eye lid, which can easily be seen in a slow worm; an ear hole, which is very small; a less flexible backbone and a solid jaw, unlike the dislocating jaw of a snake, which can eat prey much larger than itself. 

Like the common lizard the slow worm has the ability to shed its tail when under threat from a predator.  In fact the scientific name of the slow worm is Anguis fragilis which literally means ‘fragile snake’; obviously this is only partly correct. 

This shedding of the tail is only possible because lizards have special ‘fracture planes’ within some of the tail vertebrae.  When shed, the muscles in the tail will spasm so that the predator will believe it has caught something alive, allowing the slow worm to get away. The slow worm will re-grow its tail, though it is unlikely to achieve the same length or level of perfection as its original tail.

The slow worm should be regarded as a friend to us since it eats many garden pests, its favourite foods include insects, small snails, hairless caterpillars and slugs (this is one reason why we should not use slug pellets in our gardens, the harmful chemicals which are ingested by slugs can then be taken in by slow worms). 

September is a good month to look for slow worms. They don’t like very hot days, in fact when it becomes very hot they actually hide away and slow their bodies to a virtual shut down, a process known as aestivation. The best way to find them is to turn over logs, stones or loose paving slabs to have a look underneath.

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