After years of speculation, it's now official - grass snakes are native to Scotland.

Conventional wisdom has always maintained that the grass snake (Natrix natrix) is native to England and Wales, but not to Scotland. Its northern range edge curiously matches the Scottish border, but the occasional reports of grass snakes north of the border have always been dismissed as erroneous.

New evidence, however, has proven that grass snakes are not only present in Scotland, but are well established. Scottish ecologist Chris Cathrine of Caledonian Conservation Ltd saw a grass snake in Upper Nithsdale in 2010, which raised his interest.

Soon he had unearthed sightings from other people, and he embarked upon a reassessment of all grass snake records from Scotland. Some were certainly mistaken reports of slow-worms and adders; others were harder to dismiss.

After forensic examination of recent historical reports, he concluded that there have been at least three verified sightings from Dumfries & Galloway since 2009. Other sightings elsewhere in Scotland may originate from deliberate releases, or be a case of mistaken identity.

The full story, as reported by the Scottish Sunday Herald, can be found here:

http://www.heraldscotland.com/news/environment/ssssscotland-here-we-come.1328411185. 

Scotland is already home to adders, viviparous lizards and slow-worms; and now grass snakes are officially its fourth native reptile species.

Although some commentators are speculating that grass snakes are a recent arrival in Scotland, they may have been native there for anything up to ten thousand years. After the last Ice Age, reptiles recolonised Britain and made their way north, eventually reaching Scotland.

Climate during the prehistoric past was actually markedly warmer than today. Hence the sporadic occurrence of grass snakes in Scotland is just as likely to be a relict of a formerly wider distribution, as it is a recent dispersal.

Grass snakes are Britain's only egg-laying snakes, and rely upon rotting vegetation and manure to incubate their eggs. They can reach up to 2m (6ft) in length, but rarely exceed half this. They are usually dark green, with a creamy yellow band behind the head.