Where Do Grass Snakes Lay Their Eggs? Compost Heaps and Manure

Why do grass snakes choose compost and manure heaps?

Snake eggs need warmth to develop, and grass snakes live far enough north that the summer sun alone is often not enough. Their eggs need a temperature of at least about 21 °C (70 °F) to hatch, and they develop best at around 28 °C (82 °F) with high humidity.

Rotting plant material provides both. As bacteria and fungi break down grass cuttings, leaves, straw or dung, they release heat, and the inside of a well-stocked compost or manure heap can stay warm and moist for weeks even when the weather is cool. That makes such heaps ideal nurseries, and it is one reason the grass snake is often found close to farms, stables and gardens.

Typical egg-laying sites include:

• garden compost heaps and bins with open access at the base
• manure heaps on farms and at riding stables
• piles of sawdust, wood chips or grass cuttings
• rotting tree stumps and logs
• heaps of reeds and waterside vegetation cut during ditch and pond clearing
• in some places, natural sites such as rotting vegetation on lake shores

The same habits apply to the barred grass snake (Natrix helvetica) of Britain and western Europe, which was treated as part of the same species until 2017.

When do grass snakes lay their eggs?

Grass snakes mate in spring, mostly from late April to late May, soon after they emerge from hibernation. The females carry the developing eggs for several weeks and lay them from late June to early August, with the exact timing depending on the weather and latitude.

A female usually lays one clutch a year. She digs or pushes her way into the warm material, lays her eggs in a tunnel or hollow, and then leaves. Grass snakes provide no further care: there is no guarding and no help with hatching.

How many eggs are in a clutch?

The eggs stick together into a clump soon after they are laid. Their leathery shells let them absorb moisture and swell slightly as they develop, which is why a damp, warm site is so important.

Do grass snakes share nest sites?

Yes. Good egg-laying sites are scarce, so many females may use the same heap, sometimes returning year after year. Communal sites with hundreds of eggs are known, and in exceptional cases more than a thousand eggs from many females have been found close together in a single heap. Such sites can be vital for a whole local population, and the loss of a single large manure or compost heap can have a noticeable effect.

How do baby grass snakes hatch?

When they are ready, the young slit the leathery shell from the inside using a tiny, temporary egg tooth on the tip of the snout. They may rest with just the head poking out for a while, and if disturbed they can pull back into the shell.

Hatchlings measure about 15–20 cm (6–8 in) and look like small versions of the adults, usually with a clear pale collar. They are independent at once and soon begin hunting small prey such as tadpoles, froglets and newts. Many fall prey to birds and other predators in their first months, and the survivors spend their first winter hibernating, often in the same heaps or in burrows nearby.

Do other snakes lay eggs in compost?

Among the native snakes of Britain and northern Europe, the grass snakes are unusual in laying eggs at all. The common European adder and the smooth snake give birth to live young, which lets them breed in cooler places where eggs would not develop. Find out more in do all snakes lay eggs? and in snakes in the UK.

Grass snake eggs in the garden

Finding grass snake eggs in a compost heap is good news for a wildlife garden. Grass snakes are harmless and protected in many countries, including Britain, where the barred grass snake is protected against killing and injury. Wildlife groups suggest leaving heaps undisturbed from about June to September, when eggs may be developing, and keeping a heap in a sunny, quiet corner with access at ground level. In return, gardeners get to watch one of Europe’s most remarkable reptile life cycles close to home.