The Orchard Mason Bee

The population of honeybees has been steadily declining due to a highly infectious virus that has attacked the bee population across North America. Additionally, areas where other pollinating insects seek refuge through the winter have been destroyed from urban sprawl or agricultural spraying practices.

For any gardener who grows fruit trees or plants squash and cucumbers, pollinating insects make a great deal of difference in the amount of food they can harvest. To overcome the problem, gardeners can attract the solitary orchard mason bee. These bees are super-pollinators and their solitary nature has allowed them to withstand becoming infected with the virus. The bees are highly active early in the season, before most honeybees even come out of their hives.  However, they do not produce honey.

This small gentle bee is a native of almost the entire continental United States. Mother Nature's great spring pollinator, the orchard mason bee (Osmia Lignaria), was pollinating the fruits and flowers of the continent for millions of years before the first colonists brought the honey bee to North America.

Homeowners sometimes become concerned when they see the bee entering cavities under shake siding or investigating nail holes or other cavities in wood during April, May, and June. These are not destructive insects, since they do not excavate holes in the wood. Therefore, no controls are recommended, although holes may be filled with caulking to prevent the bee from nesting.

The orchard mason bee is slightly smaller than a honey bee and a shiny dark blue in color. Males are smaller than females and have longer antennae and an additional tuft of light colored hairs on the face.  The picture to the left shows the male orchard mason bee.

Females have hairs on the underside of the abdomen adapted for carrying pollen.  The female uses existing holes in wood for a nest. She chooses holes slightly larger than her body, usually 1/4 to 3/8 inches in diameter.

When the daytime high temperature reaches 57°F (14 C), the orchard mason bee starts to emerge. The males emerge a few days before the females. They mate and then the female looks for places to lay her eggs.

She prefers to lay her eggs in small holes, often in tree trunks or fences. When she has found a suitable nest, the bee first places a mud plug at the bottom of the hole then brings in 15 to 20 loads of nectar and pollen which she collects from spring flowers, including apples and other fruits. If you watch the bee closely as she enters the nest, you can see the pollen on the underside of her abdomen.

When the female has provided a sufficient supply of food for the larva, she lays an egg and then seals the cell with a thin mud plug. She then provisions another cell, and continues in this fashion until the hole is nearly full. Finally the bee plasters a thick mud plug at the entrance, so that they are insulated through the winter.

Some wasps and leaf-cutter bees also build nests in such holes but their nests can be distinguished from the orchard mason bee nests by characteristics of the plug. The plug of the mason bee is always rough while the wasp prepares a smooth plug. Leaf-cutters seal the holes with chewed-up leaves. 

These bees are not aggressive and you can observe them at very close range without fear of being stung, however, be careful when walking near the bee house as male bees often swarm the female when she emerges and they tumble to the ground. After this brief period of "romance", she will immediately start her life’s work which is to make more orchard mason bees.  This makes them excellent for enhancing yards and gardens. They add beauty, activity and pollination to our plantings.

You can attract orchard mason bees into your garden by building your own "Bee House" for them. It's easy and can be made with recycled materials.

Read our article “Bee House” in the Cooking N Crafts section for instructions on making these simple bee houses.

For more information on raising bees, we suggest:

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