Mason Bees

The Orchard Mason bee is the common name of a nonsocial native bee (Osmia lignaria) that pollinates fruit trees, flowers, and vegetables. It is found throughout most of North America, particularly in wooded areas but often around homes in towns and cities.

With the declining feral or wild bee population, the Orchard Mason bee can be easily attracted to pollinate crop plants. It is a gentle, shiny blue-black metallic bee, and slightly smaller than a honey bee. Males are smaller than females and have longer antennae and an additional tuft of light colored hairs on the face. Females have hairs on the underside of the abdomen adapted for carrying pollen.

This bee does not live in a hive. In nature, it nests within hollow stems, woodpecker drillings, and insect holes found in trees or wood. Sometimes, there may be dense collections of individual nest holes, but these bees neither connect, share nests, nor help provision or protect each others' young.

They are active for only a short period of the year. They are not aggressive and they may be observed at very close range without fear of being stung, unless they are handled roughly or if trapped under clothing. They make excellent pollinating insects, but do not produce honey.

The female Orchard Mason bee visits flowers to collect pollen for its young. She uses existing holes in wood for a nest, and chooses holes slightly larger than her body, usually 1/4 to 3/8 inches in diameter. 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. Pollen can be seen on the underside of her abdomen as she enters the nest.

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. Starting the life cycle in the spring, adult males emerge from plugs first, but must wait for the later appearance of the females in order to mate. Females alone begin founding new nests in holes to make a row of five to 10 cells in each nest. Females collect the pollen and nectar and lay eggs.

Their short foraging range is about 100 yards from the nest. Activity continues for four to six weeks and then the adults die. During the summer, larvae develop inside the nests, make cocoons, and become new adults resting in the cells. With the onset of fall, the adults become dormant as they go into hibernation. These bees require some cold temperatures before spring in order to break their dormancy.

Bee houses are easy and fun to make or can be purchased commercially from several vendors. Making your own can provide you and your children with hours of fun and even more entertainment once they are hung up in your yard to entice new bee pollinating tenants. Simply take some non-treated wood (firewood, scraps of lumber) and drill holes 3 to 5 inches deep but not all the way through the wood block. A drill bit sized 5/16th of an inch works best for Mason bees including the Blue Orchard Bee. The holes are what the bees make their nests in. Each individual hole is a nest for an individual bee. That’s what makes them solitary even though the holes are all together in one block.

They will make more females if the holes are 6” to 10” deep, so you might want to invest in a long drill bit. You can make deep holes with a short bit, but you’ll have to drill several boards separately and attach them together, which can be difficult.

You can also buy books and supplies like bee straws from knoxcellars.com along with straws that already have brood inside. These straws may be stored in a refrigerator and placed out doors when fruit trees start to blossom.

Put the nest blocks up in February and the bees will usually be done building by early June. Leave them alone until at least October so the larvae inside can remain undisturbed. Then you can take them down if you want to move them to your orchard or you can leave them where they are. Put the houses up facing south to southeast to let a little morning sun on the houses. They should be somewhat sheltered from the rain.

Mason bees may not reuse the same block the next year because it is easier for them to find a new hole somewhere than it is for them to clean out and reuse an old hole. A remedy for this is to place paper or plastic drinking straws in the holes. Remove and replace them once the bees have come out. If you pull some out too early, don’t worry, just place them in a safe environment where the bees inside can escape when they are ready to emerge.



Mason bees find and use holes in the strangest places. One day I went out to use a shovel and found that a mason bee had used the hole I put in the handle to hang the shovel on a nail as a place for her brood.