In reply to ExiledScot:
> Grass snake is a bit of a generalisation with 3 different types of grass snake: grass, smooth and barred(some sourced describe as eastern and western). All differ slightly in patterns, colours, or white cheeks. None has the diamond pattern though, adults are generally bigger than adders and aren't venomous. A presence of grass snakes is said to deter Adders, as allegedly they immune to their venom and are a threat.hesths
I think it’s more that adders and grass snakes prefer different habitats. I’ve only ever seen grass snakes near slow-moving fresh water - they eat tadpoles, small fogs and newts (and allegedly fish) as well as invertebrates, caught in and around water.
Adders prefer drier moorland, heath and mountainside (especially sunny cliff tops) and so climbers see them quite often. They tend to eat more small mammals and invertebrates. I’ve seen them sunbathing at the top of many a crag in Pembroke, Devon and Cornwall, and occasionally in the Peak.
Here’s a grass snake in our garden (we have a big pond full of newts). I think most (all) British grass snakes are now thought to be Barred Grass Snakes (Natrix helvetica) but there’s still dispute about subspecies.
Post edited at 16:02