Grass Snake (Natrix natrix): Facts, Habitat and Behavior

What does a grass snake look like?

The grass snake is a slender, medium-to-large snake with a clearly defined head, round pupils and keeled scales, which have a small ridge along the middle that gives the skin a slightly rough, matte look. The upper body is usually gray, olive or greenish-brown, often with rows of small black spots along the back and sides.

The best field mark is the collar. Just behind the head sit two bright yellow, cream or white patches, each bordered behind by a dark, half-moon-shaped band. This collar is the source of its old names, ringed snake and, in German, Ringelnatter. The belly is whitish or gray with a bold black-and-white checkered pattern that varies from snake to snake.

Color is variable. Some snakes have faint collars, and fully black (melanistic) grass snakes occur, especially in cooler or mountainous areas, where dark skin helps them warm up faster. In southeastern Europe and western Asia, some grass snakes have two pale stripes running down the back.

Grass snake or barred grass snake?

Until 2017 the grass snakes of western Europe were treated as a subspecies of Natrix natrix. That year a genetic study by Carolin Kindler and colleagues showed that the western snakes form a separate species, now called the barred grass snake (Natrix helvetica). It lives in Britain, France, the Benelux countries, western Germany, Switzerland and Italy, and meets the grass snake along a narrow zone near the Rhine, where the two sometimes hybridize. A third close relative, the Iberian grass snake (Natrix astreptophora), lives in Spain, Portugal, southwestern France and northwestern Africa.

The barred grass snake usually has a row of dark vertical bars along each side and a paler, less contrasting collar. In everyday English, especially in Britain, both species are still simply called grass snakes, and their biology is very similar. The snakes in snakes in the UK are therefore barred grass snakes.

How big do grass snakes get?

Grass snakes are among the longest snakes in central and northern Europe. Females are clearly larger than males:

Adult weight is rarely recorded and depends heavily on how recently the snake has fed. Most adults weigh well under 300 g (11 oz), with large, egg-carrying females the heaviest. Hatchlings are only about 15–20 cm (6–8 in) long.

Habitat and range

The grass snake lives across most of mainland Europe east of the Rhine, from much of Scandinavia and Finland south through Germany, Poland, central Europe and the Balkans to Greece. Its range continues east through European Russia and Kazakhstan to the region around Lake Baikal in Siberia and northern Mongolia, and south to Turkey, the Caucasus and northern Iran. In the Alps it reaches about 2,000 m (6,600 ft).

It is strongly tied to water but not confined to it. Typical habitats are ponds, lakes, slow rivers, ditches, marshes, bogs and wet meadows, together with nearby woodland edges, hedgerows, field margins, parks and gardens. Over a year, a snake may move more than 1 km (0.6 mi) between hunting areas, sunny basking spots, egg-laying sites and dry places to spend the winter.

What do grass snakes eat?

Grass snakes are carnivores and specialists in amphibians. Their main prey are common toads, common frogs and other frogs, along with newts and tadpoles; young snakes start on newts, tadpoles and tiny froglets. They also catch fish, and occasionally eat small mammals, nestling birds and lizards.

They hunt actively by day, searching pond edges and swimming through shallow water, and find prey by sight and by smell, collecting scent particles with the flickering tongue. Grass snakes do not use venom or constriction: they simply seize their prey and swallow it alive, often starting with a back leg. A large female can swallow a big female common toad, whose skin toxins grass snakes tolerate. After a big meal a snake may rest and bask for days while it digests.

Behavior

Grass snakes are active by day. They regulate their body temperature by moving between sun, shade and water, flattening their bodies to soak up warmth in the morning and coiling up when it is cool. They are excellent swimmers and often cross ponds with the head held just above the surface.

In central Europe they usually spend the winter from about late September or October until March or April in a sheltered spot that does not freeze, such as a rodent burrow, a gap among roots or rocks, old masonry or a heap of compost, manure or straw.

Like all snakes, grass snakes shed their skin as they grow, at least once and usually several times a year. A few days before a shed, the eyes turn milky blue-white, a stage called being “in blue”, and the snake hides and stops hunting because it cannot see well. The old skin peels off in one piece, inside out, and whole sloughed skins are often found near ponds.

Grass snakes are shy and usually slip away long before a person sees them. When cornered they have a whole series of bluffs: they inflate or flatten the body, raise and flatten the neck somewhat like a cobra, hiss loudly and make lunging false strikes, usually with the mouth closed. If picked up they writhe, smear the attacker with a foul-smelling musk from glands near the tail, and may then play dead. This remarkable display is described in do grass snakes play dead?.

Reproduction and life cycle

Mating takes place mostly from late April to late May, soon after the snakes emerge from hibernation. Males find females by scent and sometimes many males, occasionally more than 20, court the same female at once, without fighting each other.

Females lay their eggs from late June to early August. A clutch typically holds about 10–30 white, leathery eggs that stick together in a clump. Unlike most European snakes, the grass snake actively seeks out warm places to lay: compost heaps, manure piles, sawdust, rotting tree stumps and heaps of reeds, where decay generates heat. Good sites can hold the eggs of many females, sometimes more than a thousand eggs in total. The young hatch after about one to two and a half months, depending on temperature, usually between late July and late September. More detail is in where do grass snakes lay their eggs?.

Lifespan

Grass snakes grow slowly and may live a long time. Many wild adults probably live around 10–15 years, and ages of about 20 years or more have been reported, though precise wild records are scarce. Most young snakes do not survive their first year.

Predators and threats

Grass snakes, especially young ones, have many predators: herons, storks, owls, buzzards and other birds of prey, crows and other corvids, foxes and domestic cats. Hatchlings and small juveniles are the most vulnerable, and many are eaten in their first summer.

The main human threats are the loss of ponds, wetlands and rough field margins, the decline of amphibian prey, road traffic, and the removal of compost and manure heaps that provide egg-laying sites. Some people still kill snakes out of fear, even though grass snakes are completely harmless.

Conservation status

The IUCN Red List classifies the grass snake as Least Concern because it is widespread across a huge range. Local declines are common, however, and the species is legally protected in many European countries, including Germany and Denmark. In Britain, the barred grass snake is protected against killing and injury under the Wildlife and Countryside Act 1981.

Conservation projects often focus on creating ponds for amphibians and building or maintaining compost and manure heaps as egg-laying sites, measures that also benefit gardeners who want wildlife nearby.

Myths and facts

• Myth: grass snakes are venomous. They have no venom fangs and are harmless to people. Very rare bites cause no more than minor scratches.
• Myth: the flickering tongue is a sting. The forked tongue is completely harmless; it collects scent particles and carries them to a smell organ in the roof of the mouth.
• Myth: grass snakes drink milk. Folk tales from the Baltic region and elsewhere describe house snakes drinking bowls of milk, but snakes do not drink milk.
• Fact: a “dead” grass snake may be alive. A snake lying belly-up with its mouth open and tongue hanging out is often just playing dead and will slip away once left alone.
• Fact: grass snakes are often seen swimming. A snake swimming across a pond in Europe is far more likely to be a grass snake than an adder.

Relationship with people

The grass snake has a special place in European folklore. In Lithuanian and Latvian tradition it was a sacred household snake, called žaltys in Lithuanian and zalktis in Latvian, believed to bring luck and protect the home, and stories tell of a snake king wearing a golden crown, possibly inspired by the yellow collar. Similar crowned-snake legends exist in the Spreewald region of eastern Germany.

Grass snakes are often confused with venomous adders. The common European adder is shorter and stockier, with a dark zigzag along the back and vertical pupils, while the grass snake usually has a pale collar and round pupils.