Osmia caerulescens

The Blue Mason Bee Osmia caerulescens together with Osmia leaiana, is one of the two small Osmia bees that may regularly be found in gardens. Widespread in England and Wales but not usually in large numbers. Has two flight periods; May to July and another in August. Nests in walls, cliff and old wood; using chewed leaves to construct the brood cell divisions and to seal the nest opening.

The female is dark with a bluish iridescence and black scopa under the abdomen. In Osmia leaiana the scopa is orange. The metallic green males of Osmia leaiana and Osmia caerulescens are difficult to tell apart.