Invertebrates

The mason bee Osmia uncinata - UK vulnerable

Osmia uncinata was considered to be Osmia inermis until deemed a separate species after studies on specimens in the collection at the Natural History Museum (this is a good example of the importance of keeping voucher specimens). This is a boreo-alpine bee found in areas of high forest with open glades and dead wood. In the UK, Osmia uncinata is confined to Scotland.

Habitat

This mason bee is found in clearings in native pine woods where its main forage plant, bird’s foot trefoil (Lotus corniculatus), is well-established. Where this flower is rare, bees forage on broom (Cytisus scoparius) and bilberry (Vaccinum myrtillus). Meadows on the borders of pine woods may be an important source of food (nectar to fuel their flight and pollen for their larvae). Although primarily associated with areas of Caledonian pine forest, old plantations may be suitable, as long as there is a varied ground flora. This bee is solitary, constructing its nest in cavities in the bark of pine trees. Old burrows made by the larvae of a longhorn beetle (Rhaguim inquisitor) may be important nest sites. This beetle is scarce in the UK, thus the rarity of O. uncinata may be partially due to its need for the combination of old trees in sunny positions with the beetle burrows, and nearby patches of bird’s foot trefoil.

Threats and conservation

The main threats to O. uncinata are reduction of available habitat, loss of the open areas and increasing shading of the forage plants. Dead pine wood should be retained, and the natural regeneration of the forest should be encouraged. As a species with a boreo-alpine distribution, it is likely to be negatively affected by warming of the UK climate. This bee may benefit from measures taken to conserve other species found in native pine woods.

Source

Douglas, G. 2003. Osmia uncinata Gerstaecker, a mason bee (Hymenoptera: Megachilidae). Invertebrate species dossier, Scottish Natural Heritage.