Slow worms might look like snakes but they actually descend from a different family. Snakes belong to the family of Squamata, suborder Serpentes, while slow worms are neither a worm or a snake – they're actually a legless lizard.
Slow worms are classed under the suborder Anguimorpha, which makes them very distant cousins of snakes but certainly not the same, despite outward appearances.
Slow worms have a notched tongue where each ‘fork’ is quite short and thick. Snakes have much longer, slimmer forks and the tongue reaches out much further.
A snake has no eyelids, so cannot blink. Its eyes are protected by a fixed type of scale that acts like a contact lens to keep out dust and prevent damage from scratching. Consequently, it sleeps with its eyes open. A slow worm can get some shuteye because it has a flexible eyelid and it blinks to keep its eyeball clean.
Both animals shed their skins, but snakes do it all of a piece, whereas slow worms drop little patches at a time. So if you find small deposits of reptile skin in the garden it’s most likely to have come from a growing slow worm working its way out of its old coat.
In winter, both animals brumate, which is the snake/slow worm equivalent of hibernation and doesn’t involve going completely comatose in the cold. But their choice of accommodation varies, from snakes hiding in cracks and crevices to slow worms burrowing underground.
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