Reptiles
Grass Snake
Natrix natrix · also called ringed snake, water snake
The grass snake is the snake most people in Britain actually meet: a long, olive-green animal gliding across a pond, basking on a compost heap, or vanishing into a hedge bank. It is completely harmless, and if you corner one it is more likely to flip onto its back and pretend to be dead than to make any real attempt to defend itself.
Overview
Natrix natrix is the largest and commonest snake in Britain, with females reaching 1 to 1.3 m and occasionally close to 2 m. It is olive-green, grey, or brownish with dark flank bars, and it has a bright yellow-and-black collar behind the head. It lives in damp habitats across Europe — pond edges, wet meadows, ditches, woodland margins, and gardens — and it is a strong swimmer.
An amphibian hunter
The grass snake is an active hunter that relies on frogs and toads, along with newts, fish, and the odd small mammal or nestling. It is not a constrictor; it catches prey and swallows it alive. It is also the only British snake that lays eggs, and because it needs outside heat to incubate them, females seek out compost heaps, manure piles, and rotting vegetation, sometimes gathering in numbers at a good site.
The performance
A threatened grass snake runs through an escalating routine: hissing and bluff strikes, then a foul discharge from the rear, and finally playing dead — rolling belly-up, mouth open, tongue lolling, completely limp until the threat leaves. In 2017 the British and western European populations were split off as a separate species, the barred grass snake.
Status
The grass snake is Least Concern across Europe, but it has declined in Britain and north-west Europe with the loss of wetlands, garden ponds, and traditional compost and dung heaps.
Grass Snake: common questions
Is a grass snake venomous or dangerous?
No. The grass snake has no venom and no fangs capable of injecting one, and it is entirely harmless to people and pets. It is not a constrictor either; it simply seizes prey such as frogs and fish and swallows them alive, using its flexible jaws. If handled it may hiss, make bluff strikes with a closed mouth, and smear a strong-smelling substance from glands near the tail, but it very rarely tries to bite, and a bite from the small teeth would amount to no more than fine scratches. It is one of the safest wild animals a person can encounter in Europe.
How do you tell a grass snake from an adder?
The grass snake is longer and more slender, often over a metre, with a rounded pupil, a fairly uniform olive-green, grey, or brownish body, and a bright yellow, cream, or orange collar behind the head backed by black crescents. The adder is shorter and thicker, usually under 75 cm, has a vertical slit pupil, and carries a bold continuous dark zigzag down the middle of the back with no pale collar. Behaviour helps too, and a snake seen swimming across a pond with its head up, or basking on a compost heap, is far more likely to be a grass snake, while an adder is more often coiled and basking on open heath or moorland.
Why do grass snakes lay their eggs in compost heaps?
Because they need warmth they cannot generate themselves. A grass snake is the only British snake that lays eggs, and those eggs must be kept at a fairly high, steady temperature for six to ten weeks to develop. Britain and northern Europe are near the cool edge of the species' range, and simply burying eggs in soil would not provide enough heat. The decomposition inside a compost heap, a manure pile, a heap of grass clippings, or a mound of sawdust generates exactly the gentle, constant warmth required, so females actively search these out, and a good site may attract several females that lay dozens or even hundreds of eggs together.
Do grass snakes really play dead?
Yes, and it is one of the more dramatic displays in a European reptile. If threats such as hissing, inflating the body, and striking with a closed mouth do not work, and after it has voided a pungent fluid from its cloaca, a grass snake may suddenly go limp, roll onto its back, open its mouth wide, let the tongue loll out, and sometimes smear itself with the foul secretion or even release a little blood from the mouth. It holds this pose, apparently lifeless, until it senses the danger has gone, then rights itself and moves off. The tactic, called thanatosis, works because many predators lose interest in prey that appears already dead and possibly rotten.