Adder vs Grass Snake: How to Tell UK Snakes Apart

Key differences at a glance

Britain has three native snakes, and these two are by far the most often seen. The common European adder (Vipera berus) is a viper, while the grass snake belongs to the large colubrid group of harmless snakes. They are not closely related and cannot interbreed.

British grass snakes are now classified as the barred grass snake (Natrix helvetica). Until 2017 they were treated as part of the wider grass snake species (Natrix natrix), which lives farther east in Europe. The two look and behave very similarly, so the identification tips here work for both.

If you only remember three things, remember these: zigzag means adder, collar means grass snake, and a long snake swimming in a pond is almost always a grass snake.

Pattern and color

The adder’s zigzag is its trademark. It runs from the neck to the tail tip and is usually bold and continuous. Most adders also have a dark V or X shape on top of the head and a row of dark spots along each side. Males are pale gray, cream or yellowish with a black zigzag; females are brown, tan or reddish with a dark brown zigzag.

The grass snake has no zigzag. Its body is olive green, gray-green, brown or gray, with a row of short black bars along each side. Behind the head is a collar of yellow, cream or white, edged with black. In some older snakes, especially big females, the collar can fade and become hard to see.

Both species have occasional melanistic, almost all-black individuals, though black adders are much more common than black grass snakes. In that case, check the build and the eyes.

Size and shape

Grass snakes are Britain’s longest snake. Adults are usually 70–100 cm (28–39 in) long, and big females can exceed 1 m (3.3 ft). They are slim, with a long, gradually tapering tail and a fairly narrow head.

Adders are much shorter. Most adults measure 55–65 cm (22–26 in), and British adders rarely exceed about 80 cm (31 in). They are thick-bodied, with a short tail that narrows abruptly and a broad, flat head.

Eyes and head

Close up, the eyes are a reliable clue, but only look through binoculars or a zoom lens. The adder has red, orange or coppery eyes with vertical, slit-shaped pupils, like a cat’s. The grass snake has round pupils and dark or golden eyes.

The adder’s head is broad and distinct from the neck, with the V or X marking on top. The grass snake’s head is narrower, with large, regular scales and the bright collar just behind it.

Habitat and range in the UK

Grass snakes are strongly linked to water. They swim well and are often seen in ponds, lakes, slow rivers, ditches, marshes and wet meadows, as well as in gardens with ponds and compost heaps. They live across most of England and Wales, but are rare in Scotland, found only in the far south.

Adders prefer drier, open habitats: heaths, moors, rough grassland, bogs with dry edges, woodland edges and coastal dunes. They live across mainland Britain, including much of Scotland, but in scattered pockets. Neither species lives in Ireland.

The two can overlap on heathland with ponds or wet hollows, so habitat alone is not proof. Season helps too: adders are often seen basking in early spring near their winter dens, while grass snakes become more visible in late spring and summer around water.

Behavior and defense

Both snakes are shy and usually flee. Their tactics differ when they are cornered.

An adder hisses, flattens its body and draws its neck into an S-shape, ready to strike. It may bite in self-defense if handled or trodden on. Bites are rarely fatal but always need emergency care; see Are adders dangerous?

A grass snake almost never bites. It may hiss and make false strikes with its mouth closed, and if picked up it releases a foul, garlic-smelling fluid. As a last resort it may play dead, rolling over limp with its mouth open and tongue out; read more in Do grass snakes play dead?

Diet and breeding

Grass snakes feed mainly on amphibians, especially frogs, toads and newts, and sometimes fish. They swallow prey alive without venom or constriction. Adders feed mainly on small mammals such as voles and mice, plus lizards and frogs, killing them with venom.

They also breed differently. Grass snakes are Britain’s only egg-laying snake. In June and July, females lay 8–40 leathery eggs in warm rotting vegetation such as compost and manure heaps, and the eggs hatch about 10 weeks later. Adders give birth to 3–20 live young, usually in August or September.

Look-alikes: smooth snake and slow worm

The third native snake, the smooth snake (Coronella austriaca), is harmless and very rare, found only on sandy heathland in southern England. It is gray or brown with two rows of faint dark spots, a dark crown-shaped mark on the head and a dark stripe through the eye, but no bold zigzag and no collar. It has smooth, flat scales and round pupils.

The slow worm is often mistaken for a snake, but it is a legless lizard. It is shiny, gold, bronze or gray, has no visible neck and can blink. See Is a slow worm a snake?

All of Britain’s snakes are protected by law, and none should be handled. Watch from a distance and let them move away.