Grass snakes are one of the few animals that play dead as a defence against predators.

Subspecies
There are nine subspecies of grass snake: N.n.helvetica is the largest, and is the subspecies that occurs in Britain.

Statistics
Length: 70-120 cm. Females are larger than the males, and can occasionally reach 200cm in length.

Physical description
Grass snakes are typically grey-green in colour, often with black spots and a yellow/cream/orange collar. Their colour varies according to distribution, and completely black or partial albino individuals sometimes occur. Black lines run down from their large golden eyes to their top lips. Their underside is usually white or pale yellow with a checkering of blue-black and white markings. Their forked tongues are blue-black.

Distribution
Grass snakes are distributed over much of Europe except for the far north, parts of North Africa and central Asia. Although absent from Scotland and Ireland, they are widespread in England and Wales, but have become increasingly scarce in recent years.

Habitat
They prefer damp habitats, including river banks, ponds and ditches, but they also inhabit hedgerows, woodland margins, farmland and meadows.

Diet
Grass snakes feed on tadpoles, frogs and toads, as well as fish, newts, and occasionally mice and small birds. Most hunting is done underwater, and prey is typically swallowed alive.

Behaviour
Grass snakes are active during the day and spend time basking in the sun to warm up. They hibernate from October to March, often communally in old rabbit burrows, wall crevices, in piles of manure or under tree roots. They are good swimmers - their generic name means water snake. They swim with their heads out of the water, but if disturbed, grass snakes will dive underneath and hide amongst water weeds. They can remain underwater for up to an hour. When threatened, grass snakes puff up their bodies and hiss loudly in an attempt to frighten the predator away. If contact is made, they emit a foul-smelling liquid from their anal glands (a mixture of asafoetida and faecal matter). If this fails to put off an attacker, they roll over on to their backs and play dead. They remain very still with their mouth open and their tongue hanging out for up to 15 minutes, or until the attacker loses interest. Since many carnivores will eat carrion, this seems like a strange method of defence, but it seems to work.

Reproduction
Grass snakes mate in April-May. The male follows the female about until they twist the lower parts of their bodies together and copulate. The female lays 8-40 eggs, depending on her size, in July-August. A clutch usually contains about 10 eggs held together by mucous, secreted by the glands of the oviduct, which then dries to hold the eggs together. Female grass snakes choose a warm site to lay their eggs, such as a compost heap or under rotting logs, and will often use the same egg-laying sites as other females. A communal site may contain over a thousand eggs. The females stay near the nest site for a few days. The young grass snakes have an egg tooth to help them hatch out of the leathery eggs in late August-September.

Conservation status
Grass snakes are protected under the Wildlife and Countryside Act 1981 from being killed, injured or sold. The Sardinian subspecies N.n. cetti is classified as Critically Endangered by the 2000 IUCN Red List.

Notes
Although grass snakes produce a venomous secretion that is toxic to small animals, they are harmless to humans.