Blue Mason Bee

Osmia caerulescens


Over all length 7 to 11mm. When fresh, the male has a thick pile of orange brown hairs on the abdomen and buff hairs on the face, legs and bands between the tergites. These wear off as the bee ages. The surface of the exoskeleton has a green shine in the male and blue in the larger female.


A wide range of habitats are exploited, especially gardens and brown field sites where there are plenty of flowers. Holes in fence posts or the exit holes of other insects in trees, hollow twigs and cavities in walls are used to nest in.

Status and distribution

Uncommon but widespread in southern Britain. Uncommon in Nottinghamshire and recorded twice at Netherfield Lagoons.

Best time to see

April to July.