Honeybees that were once the stuff of legend among bee enthusiasts are playing a key role in a fight against diseases fatal to the insects.

Apis mellifera mellifera, a native subspecies of dark European honeybee, were thought to have been wiped out in the British Isles.

Rumours it survived in the Highlands were found to be true in 1992. Scientists are now studying the bees to better understand viruses transmitted by Varroa destructor mites. The chocolate-coloured native dark bees are Varroa-free.

Experts involved in a European initiative called SmartBees, including scientists from the University of Aberdeen, hope they can provide previously unattainable insights into the immune system of honeybees. The native dark bees in the study are from colonies reared in a project near Beinn Eighe, a mountain in Wester Ross.

These bees originate from eggs that were harvested in 2010 from a location 200 miles (321km) from Beinn Eighe. The original site of the dark bees is kept a secret to protect them from harm.

The harvested eggs were put in small boxes which were then taped to the hands of apiarists to keep them warm. Beekeepers later placed the eggs in “foster hives” and then raised them as queens.

Margie Ramsay has been breeding dark bees with help from Scottish Natural Heritage, which runs Beinn Eighe National Nature Reserve. She said: “These queen mothers founded the bee dynasties that bred true on the isolated mountain of Beinn Eighe.

“Now after only a few years they’ve grown to produce a thriving, healthy, native dark bee population in and around the gardens, hills and crofts of Kinlochewe.” Apis mellifera mellifera were thought to have been lost after foreign honeybees were introduced to the British Isles to boost commercial honey production in the 19th Century. A bee plague called Isle of Wight Disease was thought to have decimated surviving populations during World War One.