Megachilidae: Mason Bees (Osmia spp.)

categories: Bees Megachilidae Pollinators

revision date: 2023-03-24 12:00

Pollen on the underside of Mason bee abdomen.
Mason bee with pollen on underside of abdomen
Photo by: J. Abel


There are three genera of Mason bees and closely related species (Hoplitis, Chelostoma, Osmia). Osmia is the most speciose genus with about 150 species in North America. These bees are fly-like, robust, small to moderate-sized (0.2-0.8 inches) with round, broad heads. Their wide abdomens usually lack markings or bands of hair. Most are metallic and females carry pollen in a patch of hairs on the underside of the abdomen. Mason bees use mud or other ‘masonry’ products in constructing their nests which are made in naturally occurring gaps such as cracks between rocks and stones. Osmia frequently visit orchards and some species (eg. Osmia lignaria) are important pollinators of tree fruit.