Black and the more common gray squirrels are the same species, and scientists from Anglia Ruskin University say they want to find if the darker, less common squirrels carry the "gray squirrel pox" disease that can infect Britain's native red squirrels.
About 100 gray squirrels were introduced to more than 30 sites across England, Wales, Scotland and Ireland in the late 19th and early 20th centuries, and there are currently more than 2 million of them in Britain, the BBC reported
A mutation in the gene that governs coat pigmentation is responsible for the black coloring of some of the squirrels.
The first "official U.K. sighting" of a black squirrel was in 1912, lead researcher Helen McRobie said, and they have only been spotted in Bedfordshire, Hertfordshire and Cambridgeshire.
"Although we know black squirrels are spreading, as yet we don't have evidence that they are living elsewhere in the British Isles," she said.
"We want to understand if the blacks are, in fact, spreading faster than the grays."