The two mason bees Osmia uncinata and O. inermis are found (in the UK) only in the Highlands of Scotland (see maps). They are both similar in appearance, and both are dependent on the pollen of Bird's-foot Trefoil Lotus corniculatus to stock their nests with food for the growing larvae (though recent work suggests that O. uncinata at least may be more catholic, feeding at Broom Cytisus scoparius as well). While O. inermis is found in herb-rich mountain grassland, uncinata is an insect of Scots Pine forests. The latter can be found close to villages in Strathspey - it has been seen on the edges of Grantown and Nethy Bridge, for example, and is known from two well-used forest trails farther north.

Both are UK BAP species - click here to view the BAP pages for O. inermis and O. uncinata. A complication has been introduced by the discovery of O. hyperborea - very similar to O. uncinata - in Scandinavia, and the suspicion that it may occur also in Scotland. This increases the importance of reporting Osmia and submitting specimens where possible.

The two Osmia are only active on warm days from May to July, and any bee with a reddish-brown thorax and black abdomen feeding at Bird's-foot Trefoil in the sun, in suitable habitat in the Highlands may well be one. A specimen will be needed for confirmation, but because of their rarity only one should be removed from each site. (A third, much commoner species, O. rufa, is known to occur in southern Scotland as far north as Perth. Specimens of this would nevertheless be useful too.)

O. inermis builds nests of plant material under flat stones that will warm up in the sun on south-facing scree slopes. The story of O. uncinata is a fascinating tale of interaction involving two plants, three insects, and the local miniclimate. First, the Bird's-foot Trefoil pollen source must be present in an open sunlit situation. Old Scots Pines with a thick corky bark are used by a boring beetle Rhagium inquisitor to rear their larvae. When these leave, Osmia will use the vacant galleries in warm, south-facing, open situations to build their brood cells. If the pines do not face south, the nests will not warm up enough for the larvae to develop. Finally, a parasitic wasp Chrysura hirsuta, one of the ruby-tailed wasps, lays its eggs in the Osmia cells, its larvae feeding on the tissues of the Osmia larva. This is a splendid illustration of interdependence between organisms and their habitat, and shows what really lies behind that buzz-word 'biodiversity'.

A fourth species, O. parietina, is scarce from SW Scotland southwards, and there are old records from Skye. In May 2005 it was rediscovered by Dave Beaumont (RSPB) on the Scottish islands on Oronsay. If it is there, it may occur elsewhere on the W coast. Similar to the other species, but smaller and less bulky, it is still associated with Lotus, but it not found in forests or mountains. It is another UKBAP priority species - see the BAP page.

Any records can be reported initially by email giving date, place, six-figure grid reference and any other relevant details. Directions for sending specimens will then be provided.