Grass Snake

As its name suggests, the Grass Snake favours damp areas with long grass, often close to water. Grass Snakes will cover significant distances in search of suitable hibernation sites or feeding areas and may sometimes be found in gardens or parks. Sheltered garden ponds provide a useful hunting ground during spring as individuals recently emerged from hibernation seek out frogs and their tadpoles. Although the Grass Snake is a ‘sit and wait’ predator, it is not poisonous (nor does it constrict its prey). Prey that comes within striking range is caught and held in the backwards-facing teeth before being swallowed whole. Research suggests that an adult Grass Snake can survive a whole year on just six or seven frogs. Grass Snakes are wary creatures and are often overlooked.

Behaviour and Ecology

Grass Snakes typically emerge from hibernation in March or April and spend the first few days close to the hibernaculum. They will then move away in search of food and a mate, with mating itself taking place in April or May. Females seek out nest sites where warmth is generated artificially by the surroundings. Manure and compost heaps, together with piles of rotting leaves or reeds, are ideal and it is into these that between 30 and 40 eggs are laid during June or July. Young females lay fewer eggs (typically 8-10). The eggs are deposited over a 10-12 hour period, the first few eggs being laid in quick succession, with a greater interval elapsing between the last few eggs to be laid. Depending upon the temperature, the young emerge from the eggs after some ten weeks (August-September) and are about the same length and girth as a pencil.

Although the Grass Snake rarely bites, it can put on a seemingly aggressive defence if cornered, inflating the body, hissing loudly and striking with the mouth closed. On occasion an individual will adopt a completely different form of defence by feigning death. This very convincing display involves the snake writhing onto its back, the body becoming flaccid and the mouth open with the tongue hanging out. If further provoked or caught, they will struggle violently and discharge an evil-smelling fluid from their vent.

Identification

There is a tendency for casual observers to misidentify a Grass Snake, fearing that it is actually an Adder. However, the two species (in their normal colour forms) are quite different in appearance. A fully-grown adult Grass Snake may be more than a metre in length and is typically a medium olive green or grey above, with a series or regular small black markings along the side. The yellow and black collar markings are distinctive and any snake seen in Britain with such markings will be a Grass Snake. Some individuals, though, lack these markings but the general body pattern, large size and round pupil to the eye should still be distinctive. Complete melanism is rare and has not, to my knowledge, been reported in Britain (melanism is more frequently reported in the Adder).

Grass Snake head				Grass Snake head

The use of gardens - results from Garden BirdWatch

Grass Snakes emerge from hibernation during March and April and return to their hibernacula from late October, a pattern that is reflected in the seasonality graph shown below.

Seasonality in the use made of gardens by Grass Snake

The choice of habitats and sensitivity to disturbance explains the different reporting rates for urban, suburban and rural gardens, with rural sites the most frequently used of the three.

Differences in the use of rural, suburban and urban gardens

The Grass Snake has a southerly distribution within Britain and is absent from Ireland. Click here to see a map showing the distribution of Grass Snakes within gardens at the national level, as recorded by BTO Garden BirdWatchers during 2007.

Regional variation in the use of gardens by Grass Snakes

Click here to see what the region codes on the above graph mean.