ourtesy of Exzellente Bilder.
Homeowners sometimes become concerned when they see the bee entering cavities under shake siding or investigating nail holes or other cavities in wood during March through early June. These are not destructive insects, since they do not excavate holes in the wood, though they will clean out loose debris. No controls are recommended, since no damage is done. To prevent the bee from nesting, holes may be filled with caulking.
The females use existing holes in wood for a nest. They choose holes slightly larger than their body, usually 1/4 to 3/8 inches in diameter. The bees first place a mud plug at the bottom of the hole, then brings in 15 to 20 loads of nectar and pollen which they collects from spring flowers, including apples and other fruits. If you watch the bees closely as they enter the nest, you can see the pollen on the underside of the 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. 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.
Mason Bee Egg in Pollen Mass. Image Courtesy of Red58bill
The female mason bee lives for about a month and can produce one or two eggs each day. The larva hatches from the egg after a few days and begins to eat its provisions. When the pollen-nectar mass is completely eaten in about 10 days, the larva spins a cocoon and pupates within the cell.
Near the end of the summer the bee transforms to the adult stage but remains in the cocoon throughout the winter. In the spring, when the weather has warmed up sufficiently, the males begin to emerge by chewing their way out of the cocoons and through the mud plugs. The females, which are almost always in the inner cells of the tunnel, emerge several days later. One or two weeks may be required for all the bees to emerge during cool weather.
Females mate soon after emerging and begin nesting in 3 to 4 days. The bees forage on a number of different flowers. In wooded areas, they seem to prefer ballhead waterleaf. In urban areas, dandelion and Oregon grape are commonly visited, in addition to cherries and apples.
The mason bee is non-aggressive and will sting only if handled roughly or if it should get trapped under clothing. It is less objectionable than the honey bee as a pollinator in urban areas and should be encouraged. Efforts are being made experimentally to develop large populations of these bees to use as a supplement to honey bees for fruit pollination, much as the alfalfa leaf cutting bee was developed for alfalfa seed pollination.
Populations for pollinating around a home or commercial orchard can be developed by establishing trap nests to collect the bees. Trap nests can be made by drilling holes 1/4 to 3/8 inches in diameter and 3 to 6 inches deep in pine or fir 4x4's. A "brad-point bit" leaves a nice, smooth hole. (Figure 57) Alfalfa leaf cutting bee boards with hole diameters of at least 1/4 inch can also be used. These boards are then attached to a house or other structure where bees have been seen. Some protection from rain is desirable. Boards can also be placed on dead trees or posts in wooded areas near streams where there is a good supply of mud for nest construction and wild flowers on which to forage.
Predrilled Drilled Block Infested with Mason Bees. Image Courtesy of Red 58bill.
Boards should be positioned where they will receive morning sunlight and started in March before the bees begin nesting and remove them in early to mid-summer when nesting is completed. If the boards are stored outdoors over winter (under cover to protect them from rain and snow) the bees will usually emerge in March and April. The