Head to head
European Adder vs Grass Snake
In Britain and much of northern Europe these are the two snakes you are most likely to see, and telling them apart matters, because one is venomous and one is completely harmless. The good news is that with a decent look they are easy to separate on shape, markings, pupil, and behaviour.
| European Adder | Grass Snake | |
|---|---|---|
| Venom | Venomous; the only venomous snake native to Britain | Harmless; no venom at all |
| Length | Usually 60 to 75 cm | Often over 1 m, sometimes close to 2 m |
| Build | Short and thick, with a distinct neck | Long and slender |
| Pupil | Vertical slit | Round |
| Key marking | Continuous dark zigzag down the back | Yellow, cream, or orange collar behind the head |
| Habitat | Heath, moor, bog edge, open woodland | Wet meadows, pond and river margins, gardens |
| Reproduction | Gives birth to live young | Lays eggs, often in compost or manure heaps |
| Defence | Hisses; bites as a last resort | Hisses, musks, and plays dead belly-up |
Adder vs Grass Snake: common questions
How do I know if the snake in my garden is an adder or a grass snake?
Start with size and shape. A grass snake is long and thin, frequently more than a metre, and moves fast and fluidly; an adder is shorter, rarely much over 70 cm, and looks stout with an obvious head. Then look at the back. A grass snake has, at most, faint dark bars along the flanks and a bright pale collar just behind the head; an adder has a single bold dark zigzag running the whole length of the spine. If you can see the eye, a grass snake has a round pupil and an adder a vertical one. Behaviour helps too, since a snake swimming across a pond or basking on a compost heap is a grass snake, while one coiled on open heath is more likely an adder. Black snakes are almost always melanistic adders, as all-black grass snakes are very rare.
Which is more dangerous to people and pets?
Only the adder can hurt you, and even then the risk is modest. Its venom is made for small prey, and a bite to a healthy adult causes severe local pain and swelling but is very rarely life-threatening, with no confirmed death in Britain since 1975. Bites are more serious in children, elderly people, and dogs, particularly dogs bitten on the face while investigating a snake, so a bitten pet should see a vet promptly. The grass snake cannot bite in any meaningful way and has no venom; the worst it will do is smear a foul-smelling musk on your hands. Both snakes would far rather escape than confront anything as large as a person, and almost all adder bites happen when a snake is trodden on or picked up.
Do adders and grass snakes live in the same places?
Their ranges overlap broadly across Britain and northern Europe, and you can find both in the same general landscape, but they favour different parts of it. The grass snake is tied to water and damp ground, hunting amphibians and fish around ponds, ditches, marshes, canals, and wet meadows, and it often turns up in gardens with compost heaps and ponds. The adder prefers drier, sunnier, rougher habitat with a mix of open basking ground and dense cover, such as heathland, moorland, bog margins, coastal dunes, and open woodland rides. Where a heath sits next to a wetland you might encounter either, but as a rule a snake near water is a grass snake and a snake on dry heath is an adder.