Blue Mason Bee - Osmia caerulescens


Length 8 to 10 mm. The females have large box-shaped heads and a blue metallic lustre to the abdomen giving rise to its common name, with a black pollen basket on the hind legs. The males are bronze with pale yellow hairs and a shining slope at the front of the abdomen.

Identification difficulty

Males , Females


Forest edges and clearings, flower meadows, orchards, parks and gardens.

When to see it

April to August/September.

Life History

Nests in holes, often existing cavities in dead wood and plant stems, rocks and mud walls. The female deposits her egg, adds food for the larvae, builds a small wall out of chewed leaves and creates the next chamber, where she will deposit the next egg.

UK Status

Widespread in England and Wales but more common in the South.

VC55 Status

Occasional in Leicestershire and Rutland.

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Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map