UK Reptiles

Sunday the 8th October was a very special day for me. I saw an absolutely beautiful animal for the first time, and it marked a special occasion for me. I shall reveal both the creature and what it represents at the end of the blog post, but you will probably be able to guess before you reach it.

In celebration of the occasion, here is a blog post devoted to the UK’s 6 Reptiles – appearance, behaviour, physiology distribution etc.  It is a collection of information on all the reptiles, and I aim to delve into a bit of biology with each that I haven’t found collected in one place on the internet so far. I hope you find it interesting.

Let’s kick off with the UK’s most common snake – the grass snake.

Grass snakes have a grey-green body with black bars running down the sides, however their most distinctive feature is the yellow and black collar around their neck. They can grow over 6ft in length, taller than a man!
Males often have longer thinner tails, and are smaller than the females.

They can be found all throughout England and Wales, with a population, from an estimate of about 5 years ago, of 320,000 individuals. They feed mainly on amphibians and fish, and have the ability to swim – hence their other, more accurate name, the ‘water snake’.
They do this by creating S shapes with their bodies, and pushing those curves outwards and backwards like a paddle against the water, allowing them to race over the surface over the water with ease. It’s incredible.

As unique as our fingerprints, grass snakes have varied patterns on their stomachs, which can be used to discern between individuals, learn their ages and monitor population sizes.

If you should pick one up, it will play dead – a bit too convincingly for comfort. As well as lying limp across your hands, mouth agape and tongue hanging out, it can produce an extremely foul-smelling liquid, which is designed to give the effect of a rotten carcass. The hope is that this will deter any predators from trying to eat it. The only implication for humans is a horrible smell that will be very difficult to get rid of.
When my dad once handled a grass snake, he had to throw away the set of clothes he was wearing, because the scent wouldn’t go.

They are also the only British snake to lay eggs, rather than give birth to live young. They lay these in compost heaps and piles of cut grass where the natural heat from decomposing materials keeps them warm.
Interestingly, the warmth that they are incubated at affects a number of characteristics of the developing snake.
For example, if they are incubated at 31 degrees rather than 19, they will:
a) Require roughly 30 days less incubation before they hatch! (~25 rather than ~55)
b) Increase quite significantly in mass
c) have more predominantly yellow spots rather than white
d) exhibit less defensive behaviour.

With a lot of reptiles, the temperature of incubation can effect the sex of the individual. This is called Temperature Sex Determination. However, I’m not sure if this applies to grass snakes.

There was in interesting story in the news about grass snakes, not too long ago. Scientists analysed genetic samples and discovered that our UK grass snake is actually a different species to those found in the rest of Europe.
Before 2016, all grass snakes were considered the same species, Natrix natrix, with 14 subspecies distributed around the globe. However, last year scientists proposed that the Grass snakes in Iberia and North Africa should be considered a separate species, Natrix astreptophora. Continuing their research, they also decided that all species in Western Europe (the Rhine acts roughly as a divider) should be renamed as Natrix helvitica, while all in Eastern Europe should remain Natrix natrix.  They based this on genetic samples that they took across Europe. They identified contact zones (places where two diverging species mix and interbreed) around the Rhine area, which allows them to assess just how different the populations are and whether they should truly be considered separate species, or simply subspecies.
I’m not sure if this reclassification is officially verified yet.

The UK’s most common lizard is the Common Lizard (it makes sense). It is predominantly brown, about 15cm long, with patterns of spots and stripes. There is a lot of variation within the species, and yellow, red and greenish lizards can be found, some of which can be easily confused with the rarer sand lizard.
Males usually have orange stomachs with black spots, and females a plain cream stomach, such as the one below. 

They are distributed throughout the British Isles – yes, that means Scotland too! It has even been found in the Arctic Circle; meaning that it is the most Northerly distributed reptile, which I find impressive. They feed mainly on spiders and insects.

It is also known as the viviparous lizard, because it gives birth to live young, a behaviour rare among lizards. The advantage of such a behaviour in the UK is that it means the young are protected from the cold inside the thermoreuglated body of the mother. Once hatched, there is no maternal care – the young lizards immediately have to fend for themselves.

While Grass Snakes play dead to avoid predation, lizards have an equally gruesome but fascinating defense mechanism.  They can self-amputate their tails, in a process known as caudal autotomy. This allows them evade predators. When caught by the tail, the tail will simply fall off, and continue wriggling on the ground as a distraction to the predator while the lizard makes a hasty retreat. The tail eventually regrows.
The reason why they have the amazing ability to sever their own tails is because of a special weakness at a certain point in the vertebrae of the tail. Muscles constrict around this weak point, snapping it off, and all of the blood vessels at this point also constrict, preventing fatal blood loss.
This technique is only thought to effectively work against snakes, which have the greatest chance of catching a lizard by its tail.  In the UK, this has an additional advantage for the Common Lizard. By self-amputating, it prevents the venom injected by an adder from reaching its vital organs.
However, caudal autotomy does have its disadvantages. Counter-intuitively, tailless lizards cannot run as fast, and also grow more slowly, are less attractive to the opposite sex, and lose social standing. Not all of these necessarily apply to Common Lizards; these findings were sampled from a different species in Greece. However, I wouldn’t be surprised at all if there were similarities.

Perhaps my personal favourite is the slow worm. It’s not slow, and it’s not a worm. I think the name comes from the old English for slay, and their habit of eating worms (although their main prey is actually the slug).
They can grow up to about 40cm long, and vary in colour from the palish beige beneath to a deep rusty brown.

Males have proportionally larger heads than the females, and have a more uniform colour compared to the females, who often have a dark dorsal stripe running down their backs.

Neither is the slow worm a snake. It is in fact a legless lizard, as I’m sure you’re aware. We can tell this by the fact that it has eyelids with which it can blink, and that when caught, it has the ability to shed its tail (which snakes do not do), which gave it its Latin name of ‘Anguis Fragilis‘ meaning ‘fragile lizard’. In addition, if you were to X-ray a slow worm, you would find the remnants of the bones of limbs, so small that they are invisible from the outside.

They are ovi-viviparous, giving birth to live young inside a birth sack, containing up to 12 developed individuals. After a short while this birth sack breaks open and the slow wormlets (in absence of an official term) wriggle free, only a tiny fraction of the size of the adult (they take nearly 3 years to reach maturity!). They are so small in this period that they are at serious risk of being predated on by frogs and toads.

These lizards are smooth, good natured and a pleasure to handle, although of course you have to be careful not to trigger the tail-releasing behaviour.

The adder, on the other hand, is not really something I would feel totally comfortable handling. It is a viper,
and our only venomous snake, although they will only bite as a last resort – just like most wildlife.
The last adder death was in 1975. I don’t really worry about them on heathland, as long as I wear protective boots and don’t pick one up, it’s extremely unlikely I will be bitten. 100 people get bitten every year by adders, and none have died in the last 40 years, so there is really little to be afraid of.

Beyond their fearsome reputation, they too come with a host of interesting biology. They are the most northerly distributed snakes, for one thing.
In terms of identification, adders are quite distinctive (if you manage to pick them out from the surrounding heather). They have a black zig-zag running down their back, which is as varied between individuals as our thumbprints. They have a black slit for a pupil, unlike the vaguely similar smooth snake, which has a circular pupil.
Males are a silvery colour, whereas females are more brown, and they can grow up to 50cm long.
All of these characteristics make up for a pretty evil-looking creature, it must be admitted.

And yes, I’m sorry, this is the best photo I’ve got of an adder, despite living on a heath apparently crawling with them for ten years!

Sylvia Sheldon, an amateur naturalist who spent a lot of time studying adders, not only recognised that individual adders had different patterns, but used this fact to measure their age. She found that adders can actually live to quite an impressive age, with some recorded reaching over 30 years old.
Adders only eat between 6 and 10 animals in a year, and are able to lower their metabolisms dramatically in cooler seasons and when food is not available. They eat a wide variety of prey items, mainly small mammals but amphibians, lizards and even birds can make up part of the adders diet (you may remember a memorable episode of Springwatch where an adder was seen to take birds from a nest in a hedge).

When fighting for females, male adders put on an impressive display, entwining around each other and wrestling for dominance. While they are doing this they can actually rush forward at quite a pace. This spectacle is called ‘adder dancing’.

Once females have been mated with then they become much less active, sitting tight because they are pregnant, while males are much more active, and roam across hundreds of metres looking for food.

The UK’s rarest and most colourful lizard is the sand lizard. Stunning, isn’t it?
It is again a largely brown lizard, but in the breeding season males turn a bright, vibrant green. They are much larger than a Common Lizard, and have distinctive eye-spots (white dots surrounded by dark rings) running down their backs.

I managed to get very close indeed to this one by sitting next to a sheet of corrugated iron for twenty or so minutes, absolutely still.


Sand Lizards, as the name suggests, like sand and sandy habitats, and they are found on heathlands and coastal sand dunes.
Unlike the rest of the British lizards, Sand Lizards lay eggs. The female burrows about 8cm into the side of a sand dune, leaving behind a small hole just big enough to poke a finger into. Once she has found a location with the ideal temperature and humidity – a nice warm south-facing slope – she will lay 5 to 15 eggs, before exiting and burying the entrance to the tunnel, sealing the eggs in a safe incubation chamber. At the end of August they will hatch out, after two to three months of incubation in the natural warmth of the sand.
By following trails, you might be able to watch this behaviour for yourself. You need to look out for a series of small lizard-shaped footprints with a line in between, produced by the tail dragging on the sand. It’s pretty distinctive.

Sand Lizards have been in serious decline, but reintroduction projects are having some successes, and have restored breeding populations to areas where they have been previously locally extinct.

The lizard’s main predator in the sand dunes is probably the kestrel. In Cornwall I have seen four of these raptors scouring the cliff edges at the same time. Of course, Sand Lizards are not their only target, but in this area they are certainly on the menu.

I actually took some photos of a kestrel predating what I believe to be a Common Lizard (despite appearances) early this year, which proves it happens. I actually took them from a moving car, without realising what the kestrel had caught, so I got a very pleasant surprise when I reviewed the photos.

And finally…
The Smooth Snake.
The UK’s rarest reptile, and the one which I ticked off last from the list – on Sunday the 8th. I have now seen every British reptile!

Smooth snakes are beautiful, looking at first very adder-like, but with a few key differences upon closer inspection. The pattern on its back is less well-formed, with pairs of spots rather than a zig-zag, and its body is slimmer. Its head is darker than the rest of its body, with a little notch at the base. But the most distinctive feature is the round pupil, making it seem much more innocent than the slit-eyed adder.
They can grow up to 70cm long, live for 20 years and give birth to live young, up to 15 individuals at a time.

Smooth snakes are so called because of the fact that they don’t have any ridges on their scales, which makes them much more smooth to touch.
Unlike adders, Smooth snakes are constrictors, and suffocate their prey to kill it. It eats mainly lizards – Common and Sand (which like the same habitat as it does). It will also take smaller snakes.
Like grass snakes, they can excrete a smelly liquid from the anal glands as a defence mechanism.

Other than this, I have struggled to find any more information about the smooth snake, perhaps because their rarity makes them a much less-studied creature.

It is estimated that there are only 3,500 of these snakes in the UK (compared to, for example, 3.5 million resident blue tits in the UK to give you an idea of the scale) although they are so elusive that there could well be more.
They are so rare because of their restriction to sandy heathlands, which are a severely declining habitat. It is estimated that we are losing 15% of it every decade, and nearly 75% is in poor condition (heathland requires regular and careful maintenance, or it will turn into coniferous forest).
They are only found on a selection of heaths in Dorset, Hampshire and Surrey, with a few reintroduced populations in Devon and West Sussex.
One thing is for certain: I am very lucky to have seen it. Naturalists have gone decades without setting eyes on one, and after 10 years of searching my time finally came. It is absolutely beautiful, and I am fortunate to live this close to a site where I can find them.
Although I have now seen every species, as you will have seen, I lack good photos of all of them, and so there’s a challenge for me for next year!

TIPS FOR REPTILE WATCHING

– WALK SOFTLY – Although snakes have no visible ears and cannot pick up vibrations through the air like we can (so speak as loud as you like!) they do have the remnants of hearing apparatus in their heads, connected to their jawbones, which makes them very good at detecting vibrations in the ground.

– LOOK UNDER CORRUGATED IRON – Reptiles love them! They provide shelter and warmth. If you go to a well-managed heathland in southern England, there are quite likely to be several pieces of corrugated iron left about by the ARC trust. Have a look.

– THINK TWICE BEFORE HANDLING – Although adder attacks are rare, trying to handle them is practically asking for it. Make sure you know what you’re doing before you attempt it.
Also bear in mind that both Sand Lizards and Smooth Snakes are highly protected, making it illegal to handle or disturb them in any way.

– HEAD OUT EARLY – The best time to look for snakes is early in the morning on a warm day after a series of cold/wet ones. Reptiles will be sluggish early in the morning while they bask to warm up, so it is much easier to see them.

-IT’S A BIT LATE NOW THOUGH – Snakes go into hibernation about now, seeking refuge in mouse holes in the ground and staying there overwinter. However, on sunny, warm autumn days and even the odd freak warm day in the middle of winter can draw out some reptiles.
For the best chances, wait until spring, but in the meantime, there’s plenty of other wildlife about, so why not check for snakes at the same time?

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