Species Spotlight: Slow Worm

A very exciting Species Spotlight this week as we look at a rarity for our project - a reptile! User rachall1 photographed a common slow worm (Anguis fragilis) last week, which is only the second reptile we've had all project.

The slow worm is NOT a worm (although, to be fair, it's not the quickest). It is actually a lizard! This is a great example of why we have scientific names for organisms (the latin bit in brackets above). The common names for species are often much older than the scientific (binomial) name - the binomial system was only formally introduced in the early 18th Century by Carl Linnaeus, well before much of our current taxonomic knowledge was founded. The binomial name, as well as avoiding confusion between a single species that have lots of common name (looking at you cougar/puma/mountain lion/catamount/panther/painter/ghost cat/red tiger/silver lion....), also tells us something about the taxonomy and evolution of the species. The Anguis genus is a group of legless lizards, and we can follow its family tree back to see its in the Anguidae family, which is a family of lizards.

So let's take a look at this lizard. It's found throughout the UK, although it's most common in Wales, as well as much of Central and Western Europe. Along with the sand and viviparous lizards, it is one of only three lizard species in the UK (and ten reptile species overall), and as such it is granted protected status, meaning it is illegal to harm or kill them (not that our domestic cats pay any attention to this law - they are their biggest cause of mortality).

Slow worms are semi-fossorial, meaning they spend much of their time hiding underneath things, such as compost piles and leaf litter. They are able to shed their tail in order to flee from danger, which is one of the tell-tail (sorry) signs that they're not a snake. Let's take a closer look at this snake/lizard confusion...

Snakes and lizards are part of the same order of reptiles (Squamata/the squamates), but they belong to different groups within this order. The exact details are a little bit complex for this blog post (I've said it before and I'll say it again and again and again: nothing is ever straightforward in biology!), but a relatable (another terrible pun) example is this:
Imagine you are a lizard. Everyone in your family that shares the same Nain/Grandma as you is also a lizard. Your distant cousins are all snakes, and they have a different Nain. However, you all have the same Naina/Great Grandma, so you're all squamates!

Anyway, I promise this is going somewhere - I know you're all here to find out "Where are their legs?!"
Well, looking again at the family tree, the ancestors of these lizards (the slow worm group) lost their legs at some point during their evolution, but their even more ancient ancestors did have legs at some point. Looking at the evolutionary history of animals is much better way of categorising them compared to their morphology. A slow worm may look like a snake due it is legless nature, but the family history tells us otherwise. Other features that distinguish these lizards from snakes are their aforementioned ability to shed their tail, and the fact that they blink with their eyelids (snakes don't have eyelids - they just have a clear scale covering their eyes).

Losing things and/or discovering new things is a very common trait of evolutionary families, and the precise reasons why are as various as the examples themselves (although it always boils down to the fact that, at some point in time, a particularly characteristic was no longer necessary/now very necessary). The ancestors of penguins could fly, but penguins lost the ability; snakes and legless lizards lost the legs that the rest of the squamates have; birds lost their teeth.

So now we know a bit more about telling slow worms and snakes apart... but telling slow worms apart is a different story! They are something called a species complex, where several distinct species look very, very similar, to the point where their morphology can't really help. This is basically the opposite problem to the one posed last week by the Harlequin Ladybird! However, I think we've probably had enough taxonomy for one week, but I'll return to species complexes in the future when I put a butterfly under the Species Spotlight! For now, check out local woodland edges, grasslands or meadows to find slow worms near you (just don't bring your cat).

Diolch and hwyl fawr
Kieran

Julkaistu elokuu 11, 2021 03:36 IP. käyttäjältä kieran-182 kieran-182

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