Researchers from Anglia Ruskin University in Cambridge believe they have worked out why black squirrels are black.
The experts say they are grey squirrels that have a faulty gene so their their individual hairs do not have white or orange in them.
Grey squirrels actually have fur made up of white, black, and orange hairs which give them their grey appearance.
Helen McRobie, of Anglia Ruskin University, said: “Our research shows that one hormone turns the switch on to make black fur, and a different hormone turns the switch off to make orange and white fur. So in the grey squirrel, as the fur is growing, the switch turns on and off to make the stripes.
“However, in the black squirrel, because there is a piece of DNA missing, a piece of the switch is also missing.
"The first hormone that switches it on still works and black fur is made, but the second hormone that should switch off, actually switches on as well. The off switch fails and the black fur continues to grow.”
A similar genetic mutation is found in the black jaguar.
The first black squirrel in the UK was spotted in Woburn, Bedfordshire, in 1912.
Over the last two years, 6,100 recordings have been submitted by the public to the Black Squirrel Project which show they have now spread as far as South West England, Wales and Southern Scotland.
Building work will start next month on a £6 million business centre at Anglia Ruskin University's Chelmsford campus.
The Anglia Ruskin University Medical Business Innovation Centre (MedBIC) will support new medical technology companies.
The new centre will open in spring 2014, and is expected to create up to 120 jobs in its first three years. It will house engineering research laboratories, offices and meeting space. Anglia Ruskin, Chelmsford City Council and Essex County Council are collaborating on the project.
Professor Michael Thorne, Vice Chancellor of Anglia Ruskin University, said: “Our aim is that the Anglia Ruskin University MedBIC, combined with the Anglia Ruskin MedTech Campus, will help Essex become a world-renowned centre of excellence for innovation.”
A man from Burwell is due to be sentenced on the 27th April for making a 'microwave bomb' which brought Cambridge city centre to a standstill.
Last month Robert Baker, 27, pleaded guilty to placing a suspect device in a microwave.
On the 27th September 2011 military bomb experts were deployed from RAF Wittering after Baker, of Toyse Lane in Burwell, placed a plastic drinks bottle containing copper piping inside a microwave at Wellington House.
The offices, which are on East Road in Cambridge, were evacuated along with parts of Anglia Ruskin University. Hundreds of office workers and students were locked out for six hours while police searched the area.