Mason bees are so named because they pack mud into their nests, like brick masons.
Illustration By Keith Ward
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
The Mason Bee (Osmia species)
In areas where cool temperatures limit honeybee activity during the spring blooming of fruit trees and blueberries, native mason bees are the pollinators that get the job done. Smaller than honeybees with dark bodies that often have a metallic sheen, mason bees can work blossoms at lower temperatures than honeybees. In much of North America, mason bees emerge when the redbuds bloom, with populations highest during apple blossom time.
Sometimes called orchard bees or blue orchard bees, most mason bees are solitary insects that nest in holes in trees, or in hollow stems of old elderberries, brambles or similar vegetation. Mason bees are so named because they pack mud into their nests, like brick masons.
Females are motivated to collect pollen because they include a ball of pollen with each egg they pack away into a mud-lined cell. After six weeks or so of busy pollen and mud collection, adult mason bees die and there is no further activity until the following spring.
Mason Bees Are Prolific Pollinators
Adult mason bees sip nectar as they gather pollen from a wide assortment of flowers, but they prefer to find good pollen sources within 300 feet of their nests.
Up to 1,500 blossoms per day must be visited to gather enough pollen to provision the next generation, so mason bees can be phenomenally efficient pollinators of fruits. Only three female mason bees can serve the pollination needs of a mature apple tree.
How to Attract Mason Bees
Grow plants that bloom in late spring (penstemon, roses) after local fruit trees finish flowering, to extend the foraging time for mason bees. If the weather is dry, provide a shallow pan of mud near your water source. Mason bees prefer mud made from clay soil.
Most mason bees nest in holes made by woodpeckers or other insects. If your property includes woods, leave dead trees standing to accommodate this food/habitat chain. In orchards or suburban environments, mason bee populations can be doubled by using man-made nesting boxes made of wood or straw. However, some native species are rarely found in nesting boxes or tubes, and it is thought these species make nests in the ground as do many other helpful wasps and bees. If you have a spot that gets morning sun that can be kept mowed high, you have a perfect site for a native bee nesting area.
More information about mason bees is available from North Carolina State University, Washington State University, and the British Columbia Ministry of Agriculture.