Something long and thin wriggles past you in the countryside. The knee-jerk response may be that you’ve just seen a snake but how can you be certain that what you’ve seen isn’t a slow worm instead? Let’s take a closer look at slow worms and the different species of snake present in the UK to give you a better idea of how to correctly identify and distinguish between snakes and slow worms.
There are a number of factors that can help us to tell the difference between slow worms and snakes. Some are “dead certs” – almost guaranteed to ensure you have the correct identification – whilst others are less certain and in these cases it may be necessary to use a number of different factors in order to be reasonably confident about an identification.
This is especially so if you only had a fleeting glimpse out of the corner of your eye rather than a good long look at the reptile in question. Wherever possible – both to make identification easier and to serve as a reminder in the future – try to take a few photographs of the animal in question.
These don’t need to be “award winning” nature photographs – certainly mine aren’t – but when a creature could vanish at any second grabbing a few quick pictures that you can analyze at your leisure later on can not only make your identifications more accurate but also more enjoyable as you sit and ponder them at a later date in the comfort of your own home.
Whilst the body of most snakes tends to taper gently from the mid section down to a fine point at the end of the tail the slow worm typically appears far chunkier with the “tail” appearing far blunter and ending far more sharply. In addition, be aware that unlike snakes, slow worms can “drop” their tails like many other lizards and so this can lead to an even “stubbier-looking” tail than normal.
The head shape differs between slow worms and snakes but it can be quite a subtle feature so isn’t recommended as the only identification source. In general the species of British snakes tend to have rather flatter-looking heads than the higher, rounder head of the slow worm. Remember that the slow worm is a lizard and not a snake and when you look closely at them it can be quite easy to see that their head is more lizard-like than snake-like.
Grass snakes, smooth snakes and adders all typically have quite clearly-defined patterns to help with camouflage. Spots and stripes are common in these species while the slow worm is typically a reasonably uniform brown in colour. Younger specimens may have stripes of colour but these tend to be longitudinal (from head to tail) rather than the more lateral marking of, for example, an adder.
British snakes feed on a variety of prey including frogs and small mammals but slow worms are rather different in that they prefer small invertebrate prey. Slugs are a perfect example of the type of food they enjoy and so should you see a “slow worm” eating a frog for example, it’s almost certainly actually a snake.
Snakes have sealed eyelids through which they see which makes them appear to have no eyelids. As a result they are also incapable of blinking. As lizards however, slow worms do have eye lids and with patience you may even see them blink. Blinking, therefore, is a guaranteed indicator that what you have seen is a slow worm and not a snake.
Of course baby snakes are smaller than adults but overall slow worms are far smaller than most of the British species of snake. Baby slow worms – which are born live rather than in egg form – can be just a few inches long and even the adult rarely exceed more than a foot. Compare this to the size that an adder or a grass snake may achieve and a smaller-sized, serpent-like creature is more likely to be a slow worm than a snake.
Thanks to their preferred prey, slow worms are most likely to be seen after rain and/or in the early evening where they will be searching for small invertebrates to eat. In contrast adders and grass snakes are often seen basking in the heat of the day though a slow worm that has been disturbed from it’s hiding place may still be seen at these times of day.
Adders, generally, seem to prefer heathland habitats, grass snakes those with open water in the form of ponds or streams while slow worms can be seen in a variety of habitats though grassland areas is where they are most often observed.
Telling a slow worm from a snake can take a little practise but hopefully you can see there are a number of factors that you can use to help you make a definitive identification.