Lovely little creatures, Slow Worms are well known for being the little gems of buried treasure you find under pieces of old corrugated metal, or at the end of the garden. And even more well-known from the textbook saying, “it isn’t a snake, it’s a legless lizard”. Which we’ve probably all heard said enough times now.
They’re our most commonly encountered lizard, coming in a range of patterns and colours. This is just a little overview of what they mean, and how to tell from them whether that one you’ve just found is a male, female or a juvenile.
Males + Females:
Unlike most animals one sex isn’t noticeably bigger/smaller than the other, although if you look carefully, you’ll see that males have a slightly wider jaw then the females, giving them a ‘neck’ where their body narrows behind it. This is thought to help them defend females, and in their brutal courtship, where they bite the female in the back of the head, forcing her to mate (probably not much fun for her).
The backs of slow worms are a good starting point for telling their gender, with females being anywhere from a warm gold to a dark copper on top. Males can cross over a little, sometimes being a golden-brown colour, but it’s usually much duller than the females, and usually more of a dull brown or grey.
But if you’re unsure, then you can look at their flanks. While males’ flanks are the same tone as on their back, females have contrastingly darker ones, almost always a shade of dark brown. If you’re still really unsure though, you can pick them up (gently!) and have a look at their bellies. The females’ will be even darker than their flanks-normally pitch black, while the males’ will be a pale blue/steely grey colour. (Top-tip: Do not lift them up directly above your face to look at their bellies because if they do get scared, they’ll musk all over your face. It’s not nice.)
Sometimes you’ll find some unusual makings or patterns on a Slow Worm. Melanistic (all black) or leucitic and albino individuals don’t have any association with their gender (but are extremely rare occurrences). However, you’ll find some that have blue dappling on its back. This is a sexist colour variation, almost exclusive to males (to double check see if the flanks are darker than on top).
Females also have their own colour variation-a narrow black or dark-brown dorsal line (juveniles also have these but males and most females loose them at a few months) is a near sure-sign you’ve found a female. Apart from these, all other markings on Slow Worms are usually nothing to do with gender; often unique to that individual-the tiny specks on their faces are their equivalent of fingerprints.
Juveniles:
For the first day or so after being born, Slow Worms will be a pale silver colour with a slight green hue; a thin dorsal stripe running down their back and pure black flanks and underside. After a few weeks, this is replaced by a warm gold colour on their backs, but still with a black colour on their flanks and undersides, and the dorsal stripe is still present. This looks almost exactly like an adult females’ colour, but females won’t have black flanks, just very dark brown. They can also be up to five times bigger.
With age, the black dorsal stripe will fade a little, disappearing on all males and some females. The flanks on the females will get slightly paler too, while the males’ will rapidly get paler, turning the same colour as their back (usually a hazel brown to begin) and their bellies will go a pale silver, taking
on a blue hue with age.
A young male and the color changes he goes through.
Thanks so much for reading! I hope you learnt something new and if you’ve got any questions/other things to add feel free to comment on here or social media. If you’d like to find out more, you can have a look at my Instagram and twitter accounts or my other blogs on here.
(For more info on Slow Worms I found quite a useful link here: https://www.arc-trust.org/slow-worm ).
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