Grass Snake

A British Naturalists' Association Guide by Roger Tabor

The Grass Snake (Natrix natrix helvetica) is the largest native reptile to be found in Britain, and the female is larger than the male. (Average female 130cm and male 100cm. A big female can reach 200cm.) It is an attractive snake which can usually be identified from its yellow collar at the back of its head, which then has a further black collar band behind it.

Grass snakes are not poisonous to people, and rarely bite. If they become trapped in a corner by a predator or ourselves they will make a loud hiss sound, and angle back their head as if they are about to strike. However, usually if their “bluff” is called and they are picked up, they will go into a tight coil protecting their head and turn over, which exposes their cream and black underside, they open their mouths feigning death. At the same time they will usually release a foul smelling material from the anal area which may attract flies to walk on the inert snake. This convincing appearance of death and apparent decay must deter many predators to make it an effective defence tactic. A few minutes after the threat has disappeared the snake will come 'back to life' and return to its activities.

The overall colour of the topside of the snake is an olive green (but can be grey green to a darker browny green) and it has black vertical 'rib-like' black bands (sometimes more reduced patches) along the length of the reptile. (Do not confuse it with an Adder (Vipera berus) which is venomous, and that has a distinctive chequer board zig-zag marking along its body, and has a thicker and less elegant and slender proportions than the Grass Snake). They are a handsome animal and have noticeably round eyes and round pupils.

Grass Snakes can be seen in damp rough grassland. You may encounter a Grass Snake in your garden, especially if you have a heap of grass cuttings or compost heap, - for the snake will use the warmth generated by the heap as an incubator for its eggs. After mating in April and May the female will lay up to 40 (average 10) white eggs from June to July, and these will develop until emerging youngsters will appear in August-September. Younger females normally lay fewer eggs than older larger ones.

If you stand on a bridge looking down at a river you may see a 'v'-shaped ripple moving through the water, and just a small head visible above water. A top view allows you to see the sideways serpentine swimming action of the Grass Snake as they hunt frogs, newts or fish. They actively hunt underwater, and are fond of tadpoles. Grass Snakes can stay underwater for a significant length of time, up to an hour if evading a predator. When on land their prey will include mice and even small birds. As reptiles they do not require as much food as mammals, and they have been found to be able to survive on as little as half a dozen frogs across a year.

Grass Snakes as reptiles are active during the day, and will bask in the sun to warm up to enable their movement to be faster. They are mainly seen in the summer months, and do not usually emerge from hibernation until March-April.

Grass Snakes are an attractive and protected part of our wildlife, being protected by the Wildlife & Countryside Act, which makes it an offence to kill, injure or sell one. They can be found across Britain, but are believed to have decreased in numbers in recent years. They have been mostly reported south of a line from the Gower Peninsular across to the Humber, and are absent from Ireland.

Native UK Reptiles:
Snakes: Grass Snake (Natrix natrix), Adder (Vipera berus), Smooth Snake (Coronella austriaca).
Lizards: Slow Worm (Anguis fragilis), Common Lizard (Zootoca vivipara), Sand Lizard (Lacerta agilis).