Mason bee house. Photo credit: Dyan Eisenberger
One of the native bees to emerge early in spring is the mason bee, Osmia. There are several species of these bees found in Pennsylvania and they are active from mid-April to mid-June. The blue orchard bee (Osmia lignaria) prefers flowers in the rose family and is a valuable pollinator for apples, cherries, and plums. Research shows that blue orchard bees visit more flowers per minute than do European honeybees and they are more efficient at transferring pollen from one flower to the next.
Male mason bees emerge first in spring and the females follow several days later. Once they mate, females search for an appropriate nesting site. These are solitary bees. Each female finds her own nest, marks the entrance with her own unique scent, lays eggs in it, and then provides food for her young. Nest sites are often hollow stems or crevices. The eggs are laid from the back of the hollow forward, and the female builds a mud partition between each egg. Eggs laid toward the back become females and those toward the front, males. The female gathers both nectar and pollen to feed her larvae. The larvae pupate in the nest in mid-summer, emerge as adults in late summer and overwinter in the nest until they emerge the following spring.
Besides growing pollinator friendly plants in your garden for bees, you can also provide nesting habitats. Since mason bees like to build nests in natural tube-shaped structures, it is possible to attract them with commercial or homemade nesting boxes. These boxes should be firmly attached to a solid structure and placed in an area protected from high winds and rain (i.e., with some sort of overhang over the tubes) at least three feet above the ground. The front should face south or southeast. Obviously, there should be pollinator friendly plants nearby as well as a supply of mud (which can be manmade).
For more information visit the following sites:
Orchard Pollination: Solitary (Mason) Bees
How to Build a Mason Bee House