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Rare solitary bees in the Cairngorms

Terracotta dishes placed to act as artificial nest sites for the mountain mason bee. Photo by Hayley Wiswell.
Hayley Wiswell describes the fascinating life cycle of the mountain mason bee and some exciting work in the Cairngorms National Park to try and boost their populations.
The Cairngorms National Park is a place of sheer abundance and is home to 25 per cent of the UK’s threatened species.  Visitors come to get a glimpse of species such as the golden eagle or the red squirrel, however there is one species that is rarer than both of those, and that is the mountain mason bee. 
The Mountain Mason Bee (Osmia inermis) is a solitary bee and, as the name suggests, it lives independently and creates its own nest of carefully constructed cells, each containing a single offspring.  The female bee creates clusters of brood cells under rocks and in rock crevices using chewed leaf pulp. The brood inside the cells takes a minimum of two years to develop, sometimes four years. This staggers the emerging adults, thus allowing for years of poor weather. It relies almost entirely on bird’s-foot trefoil (Lotus corniculata) for its food. In the UK this bee has only been recorded in the central Scottish Highlands– most recently in the Blair Atholl area and at some locations the bee has not been seen for 30 years due to limited survey work. 
A project lead by Hymettus, and funded and supported by Scottish Natural Heritage and Cairngorms National Park Authority, has started this year to discover if the mountain mason bee still exists in the Blair Atholl area. Searching for the bee is very labour intensive and involves hand searching for nest sites or searching for foraging bees on warm, still days in midsummer. An alternative approach has been trialled using terracotta dishes placed out at a variety of locations to act as artificial nest sites for the bee. It is hoped that the bee will create brood cells underneath these dishes which will provide an indication of presence and also potentially population size. 
A closely related species of mason bee, the pinewood mason bee (Osmia uncinata), is another species whose UK distribution falls almost entirely within the Cairngorms National Park. Instead of using stones and rock crevices as nesting sites, this species uses the bore holes left behind by longhorn beetles in dead pine trees. It is found in pine forests in Strathspey and Deeside where there are open sunny glades with plentiful deadwood and bird’s-foot trefoil, but is rarely encountered, probably due to its specific habitat needs and secretive lifestyle. 
Another rare solitary bee which has its stronghold in the Cairngorms is the Devil’s-bit scabious mining bee (Andrena marginata), this species requires nectar and pollen exclusively from the wildflower devil’s-bit scabious. As with all mining bees, which create tunnels in the ground for their brood cells, this species needs sunny, well drained bare ground as a nesting site. With only a handful of confirmed sightings in Strathspey, this species is listed in the Cairngorms Nature Action Plan as a species of priority conservation action. In addition to funding interpretation to raise awareness of this species, Cairngorms Nature is also currently funding survey work for this species to discover more about its distribution in the Park.
So next time you are out and about in the Cairngorms National Park scanning the skies for an eagle, take a look closer to the ground and you might be lucky enough to spot one of our smaller flying rarities.

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