Grass Snakes Natrix helvetica are Britain’s largest native land reptile. As serpents, they are reviled by some, but celebrated by others as a striking member of British fauna (The Naturalist Chris Packham described them as “really, really, very, very beautiful animals.”). Hampstead Heath has the honour of supporting the closest population of these non-venomous snakes to central London, so they deserve an introduction.

Adult grass snake on Hampstead Heath © Duncan Chapman

Adult female grass snakes can reach an impressive 180cm long, although both sexes are usually less than a meter. Their slender body is coloured in shades of green or olive- varying with the individual - and usually with blacks bars along the sides. The species’ most distinctive feature is their bright yellow or cream collar. If one is captured, a look at the underside reveals a chequered pattern, which can be used to identify different individuals like a fingerprint. Grass snakes are often confused with venomous Adders Vipera berus, but adders are easily identified by the dark zigzag marking down their back. Occasionally ‘melanistic’ black forms of both species appear. In 2017, genetic analysis revealed that Northern European and British grass snakes are a separate species from their Central and Southern neighbours Natrix natrix .

Grass snakes inhabit a variety of open habitats, including gardens. Their main requirement is a nearby freshwater source which supports their major prey of amphibians. Fish, other reptiles, small mammals and birds are also taken. Springwatch footage of a grass snake raiding chicks from a Skylark nest divided opinion amongst viewers!

Grass snakes are proficient at swimming and diving so can pursue and catch their amphibious prey on land or in the water, so you might occasionally see them swimming in the ponds on Hampstead Heath. Once prey is caught, it is swallowed whole, without constriction or venom. Contrary to popular belief, snakes can’t dislocate their jaws, but they are connected by stretchy ligaments, allowing the grass snake to swallow prey larger than its head. The sharp-toothed upper mandibles can also move independently, acting like ratchets to ‘walk’ the prey into its mouth. A rather gruesome end!

The hunter can also become the hunted. Grass snakes must watch out for birds of prey, crows, herons, foxes, cats and even hedgehogs. To avoid attack from the air the snakes prefer to stay under cover, often basking in the dappled sunlight of scrub and brambles, known as ‘pattern basking’. To put off an approaching predator, grass snakes will sometimes play dead, putting on an Oscar-worthy performance by keeling over and lolling their tongue! To complete the illusion they excrete a pungent musk to smell like a rotting corpse. A captured grass snake will also release this musk along with a squirt of excrement, wrapping around the attacker to slather the smelly liquid. That’s enough to put anyone off a snack of snake!

If a female grass snake does manage to survive to adulthood and mate, she needs to find a nest site. She is the only British snake which lays eggs (Adders and Smooth Snakes give birth to live young), but it is a challenge to keep them warm in the cool British climate. The mother snake’s solution is to lay her eggs a pile of rotting vegetation - or even better, a compost pile or manure heap - where the heat from the decomposing organic matter will incubate her eggs. We try to give the snakes a helping hand on the Heath by making heaps from grass cuttings, compost and donkey manure. You can support this work by adopting a grass snake compost heap here!

The hatchling snakes measure just 16-20cm, but resemble miniature adults, with the predatory instincts to match. They will hunt tadpoles, small fish, young newts, froglets, earthworms and slugs. As the snake grows, it must shed its tough, scaly skin. It does this in one piece, like a stocking. Even the eyes are visible on the skin slough, since they are covered by a hard, transparent scale. All things being well, grass snakes can live up to 15 years in the wild.

Unfortunately, grass snakes have greatly declined in the UK. The reasons include habitat loss (e.g. to development, wetland drainage and changes in farming practices) as well as the loss of muck heaps and compost heaps in our modern landscape. As a result, grass snakes are a key species on the Heath’s annual work plan and our volunteer Reptile Monitoring Programme on Hampstead Heath is now in its 10th year.

To learn more about how we monitor grass snakes, visit our Wildlife Monitoring page, or you could join one of our regular Hampstead Heath nature walks.

We will continue to do what we can to look after these fascinating animals and you can support our work creating and maintaining wildlife habitats here.

Love grass snakes? Why not adopt a grass snake home, or buy a grass snake tote bag in our shop?

Snakes alive

Hampstead Heath Corporate Volunteering

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