Blue mason bee
A small mason bee with a striking sexual difference — the females are metallic blue-black and the males bright golden-brown, so unalike that they are routinely recorded as two species. It nests in small cavities and seals cells with chewed leaf paste rather than mud, which sets it apart from its relatives.
Can it sting?
Females have a very weak sting and essentially never use it. Males cannot sting. Safe to watch and to handle.
How to recognise it
Females are small, stocky and metallic blue-green to blue-black with black abdominal hair. Males are entirely different: golden-brown, furry, and with no metallic sheen at all.
- Females metallic blue-black; males golden-brown. The pair look nothing like each other.
- Small — noticeably smaller than the red mason bee.
- Seals cells with chewed green leaf pulp, not mud.
- Flies May to August, later than the red mason bee.
Body length 6–10 mm (typically 8 mm).
Biology
- Social organisation
Solitary
Each female builds and provisions her own nest with no workers and no caste. Most of the world's bee species.
- Nesting
- Existing cavities and tubes; Hollow stems and plant cavities
Uses small existing cavities — beetle borings, hollow stems, gaps in mortar, and the narrower tubes of a bee hotel at 4-6 mm. Cells are separated and sealed with a paste of chewed leaves rather than with mud, which is unusual within Osmia.
- Carries pollen
- Scopa on the underside of the abdomen
- On the wing
- May to August
Lifecycle
- EmergenceAdults emerge in May, several weeks after the red mason bee.May to June.
- NestingThe female provisions cells and seals them with chewed leaf paste, working alone for several weeks.Four to six weeks.
- OverwinteringThe offspring develop and overwinter in the cell, emerging the following year.Roughly ten months.
Where it lives and what it does
- Habitat
- Gardens, brownfield land, hedgerows, old walls and woodland edge with small cavities and abundant legumes.
- Distribution
- Across Europe, North Africa and into Asia, and introduced to North America.
- Behaviour
- Fast and small, favouring legumes and mints. The leaf-paste sealing is worth knowing because it means a bee hotel tube sealed with green pulp rather than mud indicates this species rather than a red mason bee.
- Pollination role
- A useful pollinator of legumes and of garden mints, and like all mason bees it carries pollen dry and sheds a good proportion of it.
High per individual, and concentrated on legumes and Lamiaceae.
- What it forages on
- Legumes and the mint family, particularly bird's-foot trefoil, vetches and garden salvias.
Honey
Produces no honey
None. One pollen loaf per cell.
Relationship with people
- How people interact with it
- A frequent and unrecognised occupant of bee hotels, usually recorded as something else because the sexes look so different from each other.
- Conservation
- Widespread and not threatened, and dependent like all cavity nesters on the retention of dead wood and hollow stems.
Sources
- Field Guide to the Bees of Great Britain and Ireland — Bloomsbury (2015) · Field guide
- The Bees of the World — Johns Hopkins University Press (2007) · Textbook
How sources are selected and weighted is set out in the sources and evidence policy.
Guides covering this bee
- Bee plants for a small gardenA small garden cannot do everything, so it should do the things large gardens usually skip: the winter and early spring gaps, and nesting habitat. Both take almost no space.
- Bee plants for a balconyBees will find a balcony several floors up, and containers can be genuinely productive. The constraints are watering, wind and depth, and the plants that handle all three are mostly Mediterranean herbs.
Tools for supporting this bee
- Plant recommendation tool
Which plant fills this specific gap?
- Bee-friendly garden planner
What should I plant in the space I actually have?
- Flowering calendar
What should I plant so that something is always in flower for bees?