A rare species of bee, which burrows deep underground, has flourished in the sand dunes of the Uist islands in the Outer Hebrides.

RSPB Scotland staff and enthusiasts have found more than 10 colonies of the northern colletes on the sandy sites, making the area the most important UK habitat for the bees.

The northern colletes is a solitary variety of so-called mining bee, and burrows into soft soil to build its nest where it stores nectar and pollen for its larvae. They differ from bumblebees and honey bees in having no worker bees. Although they toil alone and do not co-operate with each other, they nest in what are termed "aggregations" - the insect equivalent of rookeries.

It prefers gently sloping sandy banks and dunes, close to the herb-rich island machairs. It is because this soil produces a much higher diversity of flowering plant species that the bees appear to thrive in the habitat.

Jamie Boyle, RSPB Scotland's Uist warden, said yesterday: "This is really great news and extremely encouraging for this struggling and very rare species. As well as in the Uists, there are only a few other isolated UK locations that the northern colletes bee occurs, such as on the Ayrshire coast - where it was first discovered in the UK more than a century ago - on the Cumbrian coast, on Irvine Moor and on Machrihanish as well as off the northern coast of Ireland."

Previously there had been just a handful of known nesting sites in the Western Isles. But this year there has been a concerted effort, resulting in the discovery of eight nests in one small area of North Uist, separate from another bull colony on North Uist and a further two large colonies on South Uist. Other nests were even found on some of the smaller islands such as Berneray, which is linked to North Uist by a causeway.

Mr Boyle added: "Outside the UK it is really quite an unusual insect in that it occurs in very low densities around the Baltic at sea level and it is also found in alpine habitats."