Megachilidae: Mason Bees (Osmia spp.)
categories: Bees Megachilidae Pollinators
last review date: 2026-04-26 08:29
Photo by: J. Abel
Biology
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.
Attracting and Keeping Natural Enemies
and Pollinators in Your Yard and Garden
- Native plants provide essential resources.
- Native flora also provides natural overwintering sites.
- Natural dispersion from nearby habitats ensures visitation.
- Some kinds of beneficial insects predatory mites are commercially available.
- Avoid regular use of synthetic, broad-spectrum pesticides.
- Infrequent use of certain narrow-spectrum pesticides is more compatible with some beneficials.
- Extensive lawns are also not conducive to attracting beneficial insects.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- None recommended
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.