Grass snake  (Natrix natrix)

The grass snake is Britain's largest terrestrial reptile. This snake is typically olive-green, brown or greyish in colour, with a variable row of black bars along the sides, occasionally with smaller round markings along the back in double rows. The underside is off-white or yellowish with dark triangular or rectangular markings. A characteristic black and yellow collar is present behind the head, which has earned the species the alternative name of 'ringed snake' (2). Totally black (melanistic) forms and albinos occasionally arise. Males and females are generally similar in appearance, although females are often larger; males can be identified by the presence of a swelling at the base of the tail and by the fact that they have longer tails relative to females (2).

This snake is found in lowland areas of Britain. It is widespread and common in some areas of the south and south east of England, is absent from Scotland and becomes rare in central Wales (2). It is absent from Ireland, where it is said to have been expelled by Saint Patrick (4). Elsewhere it has a wide distribution in continental Europe, from southern Scandinavia to southern Italy, reaching as far east as Lake Baikal. It also occurs in northwestern Africa. Experts currently disagree as to the number of subspecies of the grass snake; British grass snakes belong to the western subspecies Natrix natrix helvetica (2).

Like all members of the genus Natrix, the grass snake is an aquatic species that is usually closely associated with water (4). They are found in habitats featuring ponds, lakes, streams, marshes and ditches, which provide access to sunshine for basking and plenty of shelter. They may be found in open woodland, rough grassland, wet heathlands, gardens, parks and hedgerows (2).

Grass snakes are difficult to observe as they are fast-moving and wary (2). Because they derive their body warmth from the environment, this snake has to bask in the sun after emerging in the morning in order to reach high enough body temperatures to be able to function efficiently and digest their prey (3). During winter, temperatures are too low, and grass snakes find frost-free places such as deep leaf litter or rock piles in which to hibernate between October and March or April (2).

Courtship and mating take place from March to June. When a male finds a receptive female, he curves his body around the female, whilst rubbing her with his head. He wraps his tail closely around the female and copulation takes place, the female then departs and searches for a nesting site (2). The grass snake is Britain's only egg laying snake (3); eggs are laid in compost or manure heaps, where the rotting vegetation creates warm conditions (2). Development of the leathery white eggs depends on the temperature, but hatching usually occurs 6-8 weeks after egg-laying. The hatchling snakes escape from the eggs by chipping at the shell with an egg tooth, which is lost shortly after hatching. Males become mature at 3 years of age, but females do not begin to breed until they reach their fourth or fifth year. After reaching maturity, males shed their skin twice a year, whereas females slough their skin once a year just before egg-laying. Grass snakes can live for up to 15 years (2).

The grass snake is an active predator of frogs, toads and newts, although fish, small mammals and young birds may also be taken. Prey is grabbed, then swallowed alive. This snake is a good swimmer, and is able to stay submerged for over half an hour (2). This species is predated upon by badgers, foxes, domestic cats, hedgehogs and a number of birds; the snakes rely on their wariness for protection but often 'play dead' when threatened, which may dissuade certain predators from killing them. When caught, they hiss loudly, release pungent and foul-smelling substances from the anal gland, and frequently strike with the head, although they do not bite (2).

The grass snake is a much maligned species, and is often an unwelcome visitor to gardens. In some habitats, basking and egg-laying sites have been reduced in numbers (5).

This species is fully protected against being sold, injured or killed in the UK under the Wildlife and Countryside Act 1981 (3). One main aim of the conservation strategy for this species is to educate people about the grass snake, and to encourage them to tolerate its presence (6).

For more on this species and other British reptiles and amphibians see: The Herpetological Conservation Trust:
http://www.hcontrst.force9.co.uk/

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk