From the team at BBC Wildlife Magazine

Snakes of the British Isles: how many are native, which are venomous, and how to identify

Meet the native and non-native snakes of the UK and the British Isles, and find out why there aren't any snakes in Ireland.

A smooth snake coiled up in heathland.
Published: June 20, 2022 at 7:00 am
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How many species of snake are native to the British Isles?

There are three native snake species in the British Isles: the grass snake, the smooth snake and the adder.

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The aesculapian snake (Zamenis longissimus) is a species found in Colwyn Bay in north Wales, Brigend in South Wales and by the Regent's Canal in London, and is thought to be the only non-native snake species known to form a breeding population in the UK.

Are slow worms snakes?

A slow worm on moss.
The slow worm is a legless lizard, native to the UK. © Kristian Bell/Getty

Despite their lack of legs, slow worms are not actually snakes, instead they are legless lizards.

Are any snakes found in Ireland?

Ireland has no native species of snakes, though slow worms have been introduced. According to legend, this lack of snakes is thanks to Saint Patrick who is said to have banished these reptiles from Ireland whilst converting the Irish people from paganism to Christianity.

However, there is a scientific reason behind this absence. The most recent Ice Age kept the island too cold for snakes. As the glaciers retreated northwards 10,000 years ago at the end of the Ice Age, so the snakes also moved northwards into western and Northern Europe. They returned to England, Wales and Scotland since these were still connected to continental Europe but met a barrier beyond Wales: The Irish Sea. The land link between Ireland and the rest of the British Isles had been severed by rising sea levels.


Native snakes of the British Isles

Barred grass snake (Natrix helvetica)

A grass snake on a woodland floor, lit up by a patch of sunlight
Grass snake on the woodland floor during the summer. © Jamie Hall/Getty

Typically referred to in the UK and British Isles as just the ‘grass snake’, this is our largest native snake species, growing up to 1.8m in length. The barred grass snake was previously considered to be a subspecies of the grass snake species, but in 2017, a taxonomic study split the grass snake and barred grass snake into distinct separate species.

The grass snake typically has a olive-green to brown body with black markings on its flanks, with a yellow and black collar marking.

After mating in spring, female grass snakes lay eggs during the summer in warm areas such as compost heaps, these eggs then hatch in the late summer months.

Adder (Vipera berus)

An adder coiled up in moss
An adder coiled up in moss. © Mark Smith/Getty

The adder is the only venomous native snake species, and the only viper, found in the UK and British Isles. It is the smallest snake species found in the UK, growing to an average length of only 60cm in length (slightly smaller than smooth snakes and half the size of barred grass snakes).

Male and female adders differ in appearance – known as sexual dimorphism. Females are light or copper brown, whilst males are light grey. Both have a dark zig-zag running down their back. Black adders can also be found, which are usually female.

Following mating in spring, females give birth to live young (known as ovoviviparity) in August or September.

Smooth snake (Coronella austriaca)

Smooth snake curled up in heather
Smooth snake in Hampshire. © Ian West/Getty

The smooth snake is the UK’s rarest snake – and in fact, the UK’s rarest reptile, restricted to sandy heaths in southern England.

Like the adder, it’s a relatively small species compared to the grass snake, and grows to between 60 to 70cm in length. It is grey or brown in colour, with dark markings along its body – which are less defined than those on an adder.

Like the adder, the smooth snake gives birth to live young in September.


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Main image: A smooth snake coiled up in heathland in the UK. © Sandra Standbridge/Getty

Authors

Megan ShersbyEditorial and digital co-ordinator at BBC Wildlife Magazine, and countryfile.com
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