When you think of a squirrel, what comes to mind? Squirrel Nutkin of Beatrix Potter fame – a rude, mischievous, impulsive RED squirrel who loves to have fun? Or are you more likely to picture our own black squirrels, widely seen around Fairfield’s orchards and green areas?

But squirrels are supposed to be either red or grey, right? Red ones are native to the UK; the greys were introduced from North America in the 1800s as a fashionable addition to country estates.

As they escaped into the wild, grey squirrels successfully competed with the native reds and took over large areas of territory. The red squirrel, once common across the UK, is now confined to Scotland, the Isle of Wight and pockets in northern England, Northern Ireland and Wales. The grey is bigger, eats more, has more litters per year and carries a pox that is deadly to reds.

But what about black squirrels? How did they get their distinctive coat? Studies in recent years have shown that rather than being a different species, black is just one of the possible hair colourings of grey squirrels. Their fur can range in colour from grey to brown-black to jet-black, but black squirrels have the same size, behaviour and habitat as greys.

New research has shown that the unusual fur colour is a result of a ‘faulty’ molecular switch coded in a squirrel’s DNA. Grey squirrels inherit a normal pigment gene from both parents, whereas black squirrels inherit a gene with a ‘missing’ piece.

Whilst being largely concentrated in Hertfordshire, Bedfordshire and Cambridgeshire, black squirrels have been sighted as far away as Scotland and Wales. Their rise is the biggest change in squirrel demographics since our native reds almost disappeared from
huge swathes of the UK countryside more than 50 years ago. 

One possibility is that the black form is at a selective advantage in terms of maintenance of body temperature. Black absorbs heat more readily than lighter colours – so perhaps the very dark squirrels survive better in cold climes, or perhaps they are better camouflaged in dark and dense woodlands.