July 13, 2024, 10:48 am | Read time: 5 minutes
Slow worms are neither blind nor are they snakes, but they look very similar to them. PETBOOK editor and biologist Saskia Schneider explains how the slow worm got its name and how to tell it apart from a snake.
If you encounter a snake-like creature in the forest, chances are it’s a slow worm. Indeed, they are among the most common reptiles in Central Europe. With their limbless, elongated bodies, they slither across the forest floor, looking confusingly similar to snakes. But don’t worry! They have neither venom nor do they bite. In the following article, we introduce you to these shy reptiles and explain how the slow worm got its name and how to tell them apart from a real snake.
Overview
Why slow worms are not snakes
The Latin name for the slow worm, Anguis fragilis, translates to “fragile snake”. However, they are not closely related to snakes; instead, they belong to the lizard family, specifically the Anguidae or slow worm family. This family consists of more than 70 species. Not all of them look like snakes. There are species that have fully functioning legs containing five toes, and others that only have small stumps.
Similar to lizards, slow worms can shed their tails when threatened. They have several predetermined breaking points where the tail simply breaks. However, unlike the tails of many other lizard species, a slow worm’s tail does not regenerate, resulting in many of them not having one at all. 1
How the slow worm lost its legs
The main reason why slow-worms look so similar to snakes is their lack of limbs. Just like snakes, these have become smaller over the course of evolution. The reason for this has not yet been clarified conclusively, but a theory exists.
Scientists assume that snakes have regressed their legs over the course of evolution because they were able to move faster and more silently on land or in water. The same is true of slow worms.
If you look at the lifestyle of native reptiles, they spend a large proportion of their time underground. With their cylindrical bodies, they can move particularly well on sediments such as sand or soil. Legs would only be a hindrance in these environments. 2
However, it is also likely that their similarity to real snakes gives the slow worm a further advantage. Just like us, other animals and predators confuse the lizards with their poisonous doppelgängers and prefer to keep their distance.
Are slow worms blind?
The German name for these animals is somewhat misleading, as these blindworms can indeed see. The term “blind” likely derives from Old High German and signifies “dazzling” or “shining”. In fact, the many small scales on their body reflect the sunlight. As a result, they glisten as they move. 3
Is it a slow worm or a snake? How to recognize the difference
Since slow worms and snakes have different evolutionary lineages, they exhibit distinct anatomical differences. However, these differences are not always immediately apparent. One of the primary differences is size: snakes can grow throughout most of their lives, whereas slow worms typically reach a maximum length of about 50 centimeters (about 19.7 inches). However, most are between 35 and 45 centimeters (13.8 and 17.7 inches) long.
The basic coloration of slow worms can vary and include shades of brown, gray, yellow, bronze, or copper. Many slow worms exhibit what is known as an eel line—a dark stripe extending from the back of the head to the tip of the tail. Some have distinct and less distinct dark spots and lines, while others have no markings at all.
An important distinguishing feature compared to snakes is the shedding or breaking off of their tail. However, you don’t want to frighten or touch them to make sure that they are a slow worm and not a snake. To tell the two apart, you should take a closer look at their heads.
Unlike snakes, slow worms have a movable eyelid, allowing them to squint their eyes or close them completely. Conversely, the slow worm’s mouth remains slightly ajar when flicking its tongue. In contrast, snakes can flick their tongues with their mouths closed due to a gap in their upper lip. 4
Are slow worms dangerous?
Slow worms are not dangerous to humans or most animals, such as dogs or cats. Their diet consists primarily of invertebrates, with slugs and earthworms making up about 90 percent of their intake. Thus, they are helpful to gardeners, although they are seldom found in gardens unless one lives near a forest. This is because they prefer vegetation-rich and moderately moist habitats in or around woodland.
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What should I do if I encounter a slow worm?
If you come across a slow worm in the forest, you should avoid them if possible to prevent causing them stress. You should avoid touching or moving them, even if they like to crawl across footpaths. There is a significant risk that the slow worm may drop its tail due to fear. If you are accompanied by a dog, it’s advisable to keep your pet leashed and guide it carefully around the reptile.
My slow worm sightings
As a child, I always thought slow worms were snakes. At first glance, their shape, and body correspond to what is generally classified as a snake. It wasn’t until a recent vacation in the Harz Mountains that I was actually able to see them in action. When they are not motionless on the path, their movement is relatively rigid when they slither. I felt more reminded of a gecko or an iguana than a snake.