Adults are usually about 8–10 mm long.
Fine-art photographic collection
Osmia caerulescens
A metallic mason bee that chews leaves into green building paste and seals a row of private nursery cells.
About this species
Blue Mason Bee
Osmia caerulescens(Linnaeus, 1758)
Information reviewed15 July 2026
Osmia caerulescens is a solitary cavity-nesting bee. Females occupy beetle holes, hollow stems, masonry and many other small cavities, dividing them into brood cells with chewed leaf material rather than mud.
Taxonomy
Animalia · Arthropoda · Insecta · Hymenoptera · Megachilidae · Osmia
Accepted taxon. · checked 2026-07-15
Europe, North Africa and western Asia, with introduced populations in North AmericaBroad range and selected reference localities — not a complete occurrence map.
Europe, North Africa and western Asia, with introduced populations in North America
Gardens, woodland edges, walls, deadwood and flower-rich open habitats with suitable cavities.
Adults fly from spring into summer; a second brood occurs in parts of the range.
Adults and larvae depend on pollen and nectar from a broad range of flowers.
Solitary; several females may nest close together without sharing brood care.
What makes this species remarkable?
The female rasps pieces from living leaves and petals, chews them into a green pulp and uses the paste as walls between her brood cells.
Nests have been recorded in beetle holes, hollow stems, masonry, old wasp cells and artificial bee hotels — an exceptional range of ready-made cavities.
Each offspring overwinters as a fully formed adult inside a silk cocoon, waiting sealed in the nest until the following flight season.
More photographs
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