Blue Mason Bee - Osmia caerulescens


    Length 8 to 10 mm. The females have a blue metallic lustre to the abdomen giving rise to its common name, with black pollen-collecting hairs underneath. The males are bronze with pale yellow hairs and a shining slope at the front of the abdomen that distinguishes this species from other bees.

    Identification difficulty

    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 not usually occurring in great numbers, though more common in the south.

    VC55 Status

    Occasional in Leicestershire and Rutland.

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    Leicestershire & Rutland Map

    MAP KEY:

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

    UK Map