The grass snake

David Chapman / 31 July 2018

Wildlife expert David Chapman introduces the grass snake, Britain's largest snake.



The grass snake is Britain’s largest snake so an encounter with one could be a bit unnerving to anyone with a slight fear of these slithery reptiles, but they are completely harmless to us and have even developed several interesting strategies intended to discourage us, and other possible predators, from getting too close.

Identifying grass snakes

Grass snakes grow to more than a metre in length, making them easily longer than the adder, which is our other commonest snake. They are timid creatures preferring to stay well away from us but their need to lay eggs in a warm place often encourages them to our gardens. Nowadays one of the most successful places for a grass snake to lay her eggs is in a compost heap, particularly one with lots of grass clippings.

Find out how to recognise slow worms, a legless lizard often mistaken for a snake

Grass snake eggs

I remember from my biology lessons at school that one feature helping to define reptiles is that they lay eggs but most British reptiles, because they live in a colder climate, cheat the system slightly. The grass snake is the only British snake which actually lays eggs; the others (adder and smooth snake) have eggs which develop inside them and hatch whilst giving birth. Holding the eggs inside their bodies enables their mothers to keep the eggs warm enough to develop but the grass snake must find somewhere which will generate heat; hence the compost heap.

The grass snake’s eggs are laid in summer, usually in June or July, and a female can remarkably lay up to 40 of them, each about an inch long. The eggs are creamy white in colour and have a soft skin. Within each is a developing grass snake and some protective embryonic fluid. If you should find any of these eggs do not be tempted to move them because within each egg a pocket of air forms at the top and this prevents the young grass snake from drowning.

Provided the temperature of the eggs remains constantly high enough the young grass snakes hatch out in late summer or early autumn. At this stage they are only about 10 to 15 cm long and are exact replicas of their parents. Typically they are green with black markings; slightly paler underneath and with a creamy-yellow collar; though the extent of this collar is variable with some showing none at all.

By October all grass snake eggs will have hatched and it is now safe to turn the compost heap if you should wish. During the winter these grass snakes, along with the adults and all our other reptiles, must hibernate. They usually find a hole underground to avoid the coldest winter temperatures.

Look after vulnerable garden birds by making sure they are well fed during cold months. Buy a range of bird seed and feeders from Saga Garden Centre.



Water snakes

Grass snakes are unusual amongst the reptile family in Britain for their liking of water. It is not unusual to see one in a lake or a garden pond swimming in pursuit of prey. They eat a wide range of prey including frogs, newts, lizards, fish, mice, voles, even birds' eggs and nestlings where they can get them. Like other reptiles grass snakes enjoy basking and this is when we are most likely to see them. Look for them anywhere where there is a mixture of grassland and wetland on days which are warm any time during the summer months.

Encouraging grass snakes into the garden

If you are keen to encourage them in your garden then make sure to dig a pond with shallow margins and leave some unkempt habitat around at least one side of it. Connectivity is key so make sure the pond connects to a hedgerow via a corridor of longer grasses and make a compost heap in a sunny spot nearby. Also provide some large stones with a south-facing slope in amongst the grasses.

Finally I recommend putting out some small corrugated metal sheets, if you have space for them. It’s amazing what wildlife you can see by looking underneath such sheets and grass snakes love to be able to warm up under them.

Find out how to create a reptile-friendly garden

Defence strategies of grass snakes

A few years ago I went on a walk with a reptile expert and he took me to a spot where he had previously put out some metal sheets, it was late summer and we found about twenty young grass snakes. Because I was with an expert I was allowed to handle the grass snakes and I became all too aware of their defensive strategies.

The first was to exude a smelly secretion from pores in their skin; this smell can be likened to dog mess and would certainly put me off eating a grass snake, if I had been thinking about doing that anyway! The next strategy is to play dead, they literally coil themselves up, turn upside down and open their mouths to look lifeless. This is a strategy which discourages predators, many of which will only attack live prey.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.