The grass snake is the largest species of British snake, and is identified by its olive green body and darkish spots or streaks on the flanks. However, colouration can vary. Grass snakes have a distinctive yellow and black collar behind the head and have round pupils.
They can often be confused with the adder which has a more thick-set body and a distinct zigzag down its back, and it also has a vertically slit pupil. The adder is venomous, whereas the grass snake is not. Adders are rarely found in gardens.
Grass snakes can also be confused with slow worms, which are not snakes but legless lizards and are much smaller, with a glassy grey/brown appearance.
Males can be told apart from females by a swelling at the base of the tail, and a longer tail in relation to the females tail.
The grass snake can range from 70-100cm (27-39in) in length.
Females tend to be longer than males, however males have a longer tail section than females.
Found in lowland areas of Britain, the grass snake is widespread and common in some areas of the south and south east of England, absent from Scotland and rare in central Wales. It is absent from Ireland.
The grass snake has become gradually scarcer over recent years throughout the UK, and has been added to the list of priority species for conservation. It is also protected under the Wildlife and Countryside Act, and the Bern Convention.
Threats to the grass snake are largely due to human activity, for example habitat loss and modification due to urbanisation, road building and agricultural intensification, loss of egg-laying sites as compost and manure heaps become rarer, and inappropriate management of grass snake habitat.
Protection measures include management of suitable habitat areas, rescue programmes for breeding grass snakes that have been disturbed, encouraging natural colonisation of new habitats and providing advice to landowners on the importance of fresh water habitats and their surroundings to grass snake survival.
The grass snake favours rough land and pastures, open woodland, wet heathlands, gardens, parks and hedgerows. They are found in habitats which feature ponds, lakes, streams, marshes and ditches, which also provide access to sunshine for basking and plenty of shelter.
Where to find them in the garden
There are a variety of suitable places in gardens which you could find grass snakes. Compost heaps are often used as egg laying grounds due to their warmth which acts as a natural incubator. Garden ponds are used as foraging grounds for their food, as are any streams or ditches that may run through or close to your garden. Banks, mounds and rubble piles are used as areas to bask in, and they can also act as hibernation sites. Areas of short and long grass interspersed will often be used for foraging (long grass) and basking (short grass).
Role in the garden
The grass snake's diet consists mainly of amphibians such as frogs, toads and newts, but they can be known to also eat small mammals, young birds and some fish.
The snakes natural predators are badgers, foxes, cats, hedgehogs and a number of birds. The snake has two tactics to dissuade certain predators from killing them - 'playing dead' and releasing pungent and foul-smelling substances from the anal gland.
Much of the snakes diet and preferred habitat is found in many gardens, particularly those with ponds. As their natural habitat is lost and modified, the snakes are relying increasingly on gardens with favourable habitat to forage for food and for nesting sites in particular. Snakes will do no damage to your garden or to you as they are not venomous and do not bite, so do not discourage them!