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Look for a distinct dark zigzag running down the snake’s back: it is the clearest usual field mark of an adder. Colour varies, however, and other features matter. A grass snake usually has a yellow-and-black collar, while a smooth snake is slimmer and has a less defined back pattern. Do not approach or handle a snake to identify it. The NHS says the adder is the UK’s only venomous wild snake, and any suspected snake bite needs prompt medical attention.
How to identify an adder
Start with the pattern on the back. An adder usually has a distinct, dark zigzag running from behind the head down its body. It may also have a V- or X-shaped marking on its head. The Wildlife Trusts describes the adder as typically around 60–80 cm long; that is a species-description measurement, not a rule for identifying an individual snake.
Colour is variable. Males are often silvery-grey, females may be lighter or reddish-brown, and black forms also occur. The Wildlife Trusts notes the adder’s red eye; Woodland Trust’s 27 August 2026 guide also describes its slit-shaped pupil. These details can support an identification only if visible from a safe distance. Do not rely on colour alone: a grey or brown snake is not necessarily an adder.
How to tell an adder from a grass snake or smooth snake
| Feature | Adder | Grass snake | Smooth snake |
|---|---|---|---|
| Back pattern | Usually a distinct dark zigzag. | Dark markings along the sides; not the adder’s characteristic back zigzag. | Dark back pattern is less well formed. |
| Other useful marks | May have a V- or X-shaped marking on the head. | Usually has a yellow-and-black collar and pale belly. | Round pupil; usually grey or dark brown. |
| Build and length | Typically around 60–80 cm, according to The Wildlife Trusts. | Can grow up to 150 cm, according to The Wildlife Trusts. | More slender than an adder; around 60–70 cm, according to The Wildlife Trusts. |
| Human safety | The UK’s only venomous wild snake, according to the NHS. | Harmless to humans, according to The Wildlife Trusts. | The supplied species descriptions do not state a human-safety classification. |
These are typical identifying features, not a validated scoring key. Pattern, body shape and the grass snake’s collar are more useful together than any single colour or habitat clue. Smooth snakes are rare in the UK and occur at only a few heathland sites, but location alone cannot confirm what you have seen.
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What to do if you see a snake
The NHS advises: “do not go near the snake, or try to catch or kill it”. Do not handle it to inspect its markings or pupil. Adders are secretive and typically move away rather than confront people, according to The Wildlife Trusts, but that is not a reason to approach one. If you can take a photo from a safe distance without going closer, it may help describe the sighting; identification is not worth risking a bite.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to do after a suspected snake bite
Get medical attention as soon as possible. The NHS says all UK snake bites should be checked promptly. Do not try to suck or cut out venom, tie anything tightly around the bitten area, or take aspirin or ibuprofen. Do not delay care because the snake seemed small, was thought to be rare, or may have been harmless.
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