7 things you never knew about the grass snake

Discover fantastic facts about Britain’s largest native terrestrial reptile. 

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Close-up of a grass snake © MDParr / Getty

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1. Cold-blooded killer

Grass snakes feed mostly on toads, frogs and newts, but also take small mammals, fish and, occasionally, birds. They cannot digest their meal if the temperature drops below 5°C.

2. Size and scales

Grass snake - Natrix natrix. swimming across canal, Wiltshire, UK

A grass snake swimming across a canal in Wiltshire © Education Images/ Getty

Regularly exceeding 1m in length, the grass snake is our biggest native terrestrial reptile. Only the introduced Aesculapian snake, which now breeds in London and North Wales, grows larger.

3. Empty threats

Lacking venom, grass snakes defend themselves by exuding a foul-smelling secretion from their anal glands. They also hiss and feign strikes at attackers, and as a last resort play dead.

4. Collared frog-catcher

The grass snake’s characteristic yellow and black collar, which is most obvious in juveniles, may deter predators through mimicry of the warning colours of wasps and other toxic insects.

5. Blue period

Prior to moulting, a grass snake’s eyes turn a cloudy blue. It’s the result of a layer of oil forming between the old and new eye scales.

6. Identity kit

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A grass snake scenting the air © Geoff Scott-Simpson / Getty 

Grass snakes’ markings are rather variable, especially the black patches on the belly and under the eyes, allowing individual animals to be recognised.

7. Big is beautiful

Mating occurs soon after emergence from hibernation in spring. Several males attempt to copulate with a receptive female simultaneously in a writhing “mating ball.” The largest females are the most popular.

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Read more amazing facts about wildlife in BBC Wildlife Magazine