Megachilidae: Mason Bees (Osmia spp.)

categories: Bees Megachilidae Pollinators

last review date: 2026-04-26 08:29

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

• Avoid regular use of synthetic, broad-spectrum pesticides.
• Infrequent use of certain narrow-spectrum pesticides is more compatible with some beneficials but generally the less chemical inputs there are, the greater and more diverse the beneficial insect community will be.
• Extensive lawns are also not conducive to attracting and retaining a diversity of beneficial insects, mites and spiders. Minimize lawn areas and maximize shrub and bush plantings.
• Many beneficials reside naturally in riparian and other ‘natural’ areas near to many back yards. Natural dispersion from these refuges ensures that some beneficials will visit back yards but they will not stay unless food, host and shelter resources are available.
• Native plants have closer affinities with native insects and therefore provide most of these resources. A garden with a good diversity of local native flora in and around back yards, will improve the abundance and diversity of local, beneficial arthropods.
• Native flora also provides natural overwintering sites for many beneficial insects and it is useful to leave at least a small area of native vegetation undisturbed during fall and winter.
• Some kinds of beneficial insects (e.g. lady beetles, lacewings, predatory mites) are available for purchase from commercial suppliers. However, benefits from introducing these beneficials are usually limited and short-lived. Upon release, commercially obtained lady beetles and lacewings often disperse and may rapidly leave your backyard despite the presence of prey and suitable nectar resources. Generally, it is more effective and sustainable to create a garden habitat that will be colonized by beneficials naturally.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• None recommended