Invertebrates

The mason bee Osmia inermis - UK vulnerable

Osmia inermis is a boreo-alpine species found at low altitudes north of the Arctic Circle and in montane locations further south. In UK, this bee occurs on the northern central lowland belt of Scotland in the altitude range of 300 to 600 m. Osmia inermis may have a minimum two-year life cycle; the first winter is passed as a pre-pupa and the second as a diapausing adult within its cocoon. Some adults may even emerge after 3 or 4 years.

Habitat

This mason bee is typically found on exposed, base-rich uplands with a diverse floristic composition. Nests are built under stones and in narrow rock crevices in sites with closely grazed, short, dry, heathery turf. These sites have a high incidence of lichens and bird’s foot trefoil (Lotus corniculatus), on which the bees forage for pollen. Other possible forage plants are bugle (Ajuga reptans) and bilberry (Vaccinium myrtillus)

Threats and conservation

This bee is under threat from the loss of suitable habitat, especially on upland calcareous grassland, which is an increasingly rare habitat in Scotland. The loss of herb-rich, short sward grasslands occurs through agricultural intensification, commercial afforestation or insufficient grazing. As a boreo-alpine species, this bee is likely to be negatively affected by warming of the UK climate.

Source

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