The great yellow has suffered from a run of poor seasons
The great yellow bumblebee - one of Britain's rarest bees - has been found at its most southerly site in 30 years.
Once widespread, its numbers declined in the face of intensive farming and has clung to survival on Orkney and the Western Isles.
The far north Highlands are home to the last mainland population.
Bob Dawson, of the Bumblebee Conservation Trust (BCT), has now discovered the species near Lybster, on the east Caithness coast.
The Stirling University-based Scottish conservation officer said its spread suggested the bumblebee has enjoyed a good summer following a run of poor ones.
Conservation efforts by farmers and landowners were also thought to have helped boost numbers.
Mr Dawson said: "This is a modest, but significant extension of the known range southwards.
"We suspect the great yellow bumblebee may have been present in this area before, but with more interest and awareness now in the great yellow bumblebee, interesting and important records like this are turning up."
He added: "There is even the tantalising possibility that the great yellow bumblebee could re-colonise the Moray and Aberdeenshire coasts."
Paul Castle, Highland Council North Sutherland ranger, said it has proved to be an exciting summer with new nesting sites also found at Melvich and Reay along the far north coast.
He said: "These new sites mean we have now linked the Caithness and Sutherland populations.
"It was particularly pleasing following last season when, despite searching, I never saw a single great yellow bumblebee.
"It's great to know this vulnerable mainland population is able to recover from an apparently disastrous season."
Dave Jones, the RSPB's Caithness reserves site manager, said the species has been recorded at the conservation charity's new Broubster Leans reserve.