Osmia / mason Bee

Family: Megachilidae

Genus: Osmia

Common Name: Mason Bee


Physical Appearance

Coloring is usually a dark metallic, ranging from green to blue.


The female carries pollen in a brush of specialized hairs, called a scopa, on the underside of her abdomen.



Osmia species are cavity or tunnel nesters, most making their nests in pre-existing wood tunnels. As opportunists, many Osmia species will readily occupy man-made wood block nests or stem bundles.


To construct brood cells, the female divides her tunnel nest with walls made of mud or chewed leaves, hence the name mason bee.


Osmia are recognized as valuable crop pollinators. Some species, such as Osmia lignaria (blue orchard bee) are now managed to pollinate orchards. Just 250 females can pollinate an acre of apple trees, a task requiring approximately 20,000 honeybees!


Size: Small to medium sized bees, usually less than ½ inch in length.



A large genus of about 350 species worldwide, found primarily in North America and temperate regions of Eurasia. Osmia species are widespread across North America, though are rare in desert regions. The greatest diversity of Osmia species is found west of the Mississippi.

Number of species in North America

Approximately 150


Emergence Time
Spring to early summer


Nesting Habit
Tunnel nesting, in pre-existing tunnels in wood or in other suitable material. Many species will adopt artificial nests of drilled wooden blocks, reed or bamboo stems.


Pollinated Garden Crops Include



Additional Flowers Visited in Natural Areas

Hydrophyllum (waterleaf)
Rubus (blackberry)

Visited Plants

Arctostaphylos / Manzanita

Asclepias / Milkweed

Ceanothus / Wild Lilac

Cercis / Redbud

Clarkia / Clarkia

Coreopsis / Tickseed

Dalea / Prairie Clover

Eriogonum / Buckwheat

Eschscholzia / California Poppy

Geranium / Wild Geranium

Holodiscus / Oceanspray

Larrea / Creosote Bush

Lavandula / Lavender

Lupinus / Lupine

Nepeta / Catmint

Penstemon / Beardtongue

Phacelia / Scorpionweed

Prunus / Plum

Rhododendron / Rhododendron

Ribes / Currant

Rosa / Rose

Salix / Willow

Salvia / Sage

Sphaeralcea / Globemallow

Vaccinium / Blueberry

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Osmia / Mason Bee

Female Osmia granulosa Cockerell. © Rollin Coville