Species Focus - Grass Snake (Natrix helvetica)

The Grass Snake is Britain’s largest snake with females reaching up to a metre in length. The sexes are similar and typically have an olive-green background colour with vertical black bars along the flanks and a distinctive yellow and black collar. The Grass Snake can be distinguished from the Adder by lacking a dark zigzag band running the length of the back. The Grass Snake is non-venomous and completely harmless to humans.

Grass Snakes are widespread in North Wales but largely restricted to lowland areas where they are associated with river valleys, lakes and ponds which provide their preferred amphibian and fish prey. Unlike the Adder which gives birth to live young, the Grass Snake lays eggs which need an external source of heat for incubation. Clutches of 10-40 eggs are laid in damp, warm, rotting vegetation in June and early July. This frequently brings snakes into gardens, allotments and farmyards in search of compost heaps and manure piles.

The species has declined in recent decades mainly due to habitat loss and declines in amphibian populations. If you live close to suitable habitat you can help by creating a compost heap suitable for egg laying. Further information can be found in the leaflet ‘Hatching a plan for grass snakes’ available on the website of the Amphibian and Reptile Conservation Trust. Look out for the pencil-sized (15 cm) hatchling snakes in late summer and for clumps of empty egg cases when using the compost later in the year. Please submit your records, ideally with photos, to the Cofnod ORS or the LERC Wales App.