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The mystery of the black squirrel in Hertfordshire

PUBLISHED: 12:43 18 October 2019

Black squirrel in Letchworth (photo: Simon A A Hawkins/Alamy Stock Photo)

Black squirrel in Letchworth (photo: Simon A A Hawkins/Alamy Stock Photo)

Credit: Simon A A Hawkins / Alamy Stock Photo

They have spread from their stronghold in Letchworth to become an increasingly common sight in Herts and beyond, but how did the black squirrel get its coat and is it the thug some believe?

Having unsuccessfully spent hours searching for one of Hertfordshire's most mysterious wild residents, I decided to call it a day on capturing an image of the elusive creature. But, as I was driving past Howard Park and Gardens in Letchworth, a black streak shot past the car. Before I had a chance to whip out my camera and snap a photo of the blessed thing, it had scampered into the bushes.

Herts is lucky to have an abundance of parks, but something most residents may not expect to see while enjoying a picnic or a game of frisbee is a small jet black creature flying from tree to tree or making a dash across the open. For some of us in Hertfordshire, as well as now in Bedfordshire and Cambridgeshire, this is becoming a common occurence. The mysterious animal? The humble grey squirrel, but with a mutant gene.

Once common across the UK, the red squirrel is now confined to Scotland, the Isle of Wight and pockets in northern England, Northern Ireland and Wales (photo: Michael_Conrad/Getty Images/iStockphoto)Once common across the UK, the red squirrel is now confined to Scotland, the Isle of Wight and pockets in northern England, Northern Ireland and Wales (photo: Michael_Conrad/Getty Images/iStockphoto)

In Herts, black squirrels are mostly found in the north of the county, in a stronghold in Letchworth and its surrounding towns, according to Herts and Middlesex Wildlife Trust. But these unusual rodents have been spotted as far away as Scotland and Wales. Recent estimates have put black squirrel populations at around 25,000 in the UK. Comparatively, there are an estimated 2.5 million grey squirrels, and around 140,000 of our native red squirrels,

which went extinct in Hertfordshire decades ago, a victim of squirrel pox - to which reds are fatally vulnerable but greys immune - and grey's ability to have two litters a year, compared to red's one.

The grey squirrel was introduced from North America back in the 1800s as a fashionable addition to country estates, but where did black squirrels come from? The first wild sightings can be traced to 1912 in Letchworth. It's thought the first black squirrels were brought over from America by the Duke of Bedford for his estate at Woburn in Bedfordshire.

Fox squirrel kit peers over its mother in a nest in a tree in Naples, Florida (photo: LagunaticPhoto/Getty Images/iStockphoto)Fox squirrel kit peers over its mother in a nest in a tree in Naples, Florida (photo: LagunaticPhoto/Getty Images/iStockphoto)

To discover why they are black, a study was initiated in 2005 by Alison Thomas, Shelia Pankhurst and Helen McRobie of Anglia Ruskin University. They discovered that rather than being a separate species, black is just one of the possible hair colourings of grey squirrels. Their fur can range from grey, as we commonly see them, to brown-black and jet black.

Introduced to the UK by Victorian landowners, the first wild population was recorded in 1876. Numbers have now reached 2.5m (photo: Bart Versteeg/Getty Images/iStockphoto)Introduced to the UK by Victorian landowners, the first wild population was recorded in 1876. Numbers have now reached 2.5m (photo: Bart Versteeg/Getty Images/iStockphoto)

A nut-loving rodent and a deadly jaguar is an unlikely comparison, yet they share a similarity - the explanation for black hair in squirrels is the same for panthers. The squirrel's colour is impacted by a naturally mutated gene that regulates the distribution of grey and black pigments. If a squirrel has the mutated gene, more black pigment is produced. Completely black squirrels must inherit a pair of these genes. The brown-black version has one, and those with a grey coat have two normal genes.

The origin of this mutated gene was a mystery until a new study published this summer. Research by Helen McRobie, Nancy Moncrief and Nicholas Mundy revealed that the gene responsible for melanism in grey squirrels was identical to a gene causing melanism in a related species, the American fox squirrel. What they believe happened was a kind of star-crossed lovers situation between a grey and a fox squirrel, and the gene was passed between the species. One of the products, or perhaps several, of this interbreeding in the US then entered a private wildlife collection in the UK.

Since their population expansion in recent years there have been unfounded media claims (with more than a hint of racism) that black squirrels are more aggressive and voracious than greys. There is however no evidence to suggest that the mutated gene impacts squirrels' behaviour. Since black and grey squirrels are the same species, they don't compete for habitat as grey and red squirrels do. And considering the rarity of black squirrels, it casts doubt on their supposed plan for domination.

According to Herts and Middlesex Wildlife Trust, any impact they do have is part of the larger negative impact of grey squirrels on reds. The Herts Biodiversity Action Plan states that grey squirrels also pose a threat to woodland by stripping bark, and their diet has the potential for long-term ecological impacts.

Classified as 'non-native invaders', it's illegal to release a grey squirrel into the wild. Rather than battling greys, black squirrels are part of the same gang causing problems for woodland and the native reds. Admittedly, because of their rarity and energetic, almost cheeky, character, black squirrels remain an exciting animal to see and can be spotted year-round. But perhaps have some nuts handy, just in case you catch them on a shy day.

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