Blue Mason Bee

Osmia caerulescens

Common & widespread in Britain.

Flies from April-August/September.

Females of Osmia caerulescens are 10–11 mm in length, dark blue-black in color, with a metallic sheen, and sparsely covered with brown hairs with those on the abdomen forming a narrow, dense, flattened band on the hind margin of each of the segments.

The dense brush of pollen-collecting scopae on the underside of the abdomen is jet black.

Males are slightly smaller, 9mm, more slender in build, distinctly metallic green and clothed with pale hairs.