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What has three body parts, builds four nests, has six legs and five eyes? If you guessed our local mason bee, you'd be right, but how did you know? Although many people appreciate the industrious pollination of social insects such as honeybees, far fewer appreciate other native pollinators such as the bumble and mason bees, who are just now starting to emerge.

Solitary Bees without Hives

In addition to well-known social bees such as honeybees and bumblebees, there are also many solitary bees. These tend not to associate much with others, and each has its own type of nest and life cycle. Indeed, for many crops (such as our northwest fruits), solitary bees are even more important than their hive-dwelling cousins. The mason bee is one of these, and understanding them can help us encourage healthier homes and stronger food systems for ourselves.

There is an entire family of solitary bees known as the Megachilidae, remarkable for the different kinds of homes they build. Leafcutter bees will cut out small bits of leaves which they roll into a kind of sleeping bag. Carder bees will collect wool or other fiber with which to build their nests. Carpenter bees will actually drill holes into wood for their young, while the mason bee uses such holes and hollow reeds to create separate chambers for its young out of mud.

Spring Orchard or Mason Bees

Of this family, the most important local species is the Osmia lignaria, known variously as the orchard bee, blue orchard bee, spring orchard bee or mason bee. These tend to emerge after the temperature rises above 55 degrees for several days in a row, immediately mating and then proceeding to pollinate within a couple hundred feet of their home as they find new homes for their young and build their distinctive nests.

Life Cycle of the Mason Bee

Lignaria eggs are laid within a series of mud chambers, placed in a hole, piece of straw or reed about the width of a pencil and 6" or so deep. Female eggs are laid in the rear of the hole, given a meal of pollen and nectar "bee bread" then sealed in against the winter with mud. Usually several eggs will be laid in each nest ( females in the rear and males up front), each female bee building three to five separate nests. Collecting the pollen and nectar for each egg takes about two dozen separate trips, and then the mud is added and more eggs laid, each in its own chamber with its own bee bread.

From Egg to Larva, Cocoon, Pupa, Adult

Within a few days of being laid and enclosed, the egg will open to reveal a larva, which immediately begins eating its food within the chamber to "fatten up" and then begin to spin its cocoon after about a month. The fresh cocoon is pinkish at first, but changes color to a sort of husky brown as it sits basically unchanged for another month. The pupa is a separate distinct life stage within the cocoon, and it is within the pupa's shell that metamorphosis occurs and from which the adult stage or imago emerges, all within the mud chamber. The adult is basically in a state of suspended animation, "sleeping" for the winter months until temperature triggers emergence in the spring, usually near the end of March or the beginning of April.

Emergence, Mating, Pollination and New Nests

When it is time to emerge, adults will begin to break down the mud walls of their cells, with those closest to the warm outside air first. Because males are laid farther out than the females, they emerge first and loiter in the area. As the females emerge, mating occurs, the males dying within a few days. Females will live for about a month, searching for new nesting sites, laying eggs, gathering food for the eggs and sealing off the cells for each egg.

Because lignaria emerge early in the spring, they are dependent on the existence of flowers immediately. Much more efficient pollinators than honey bees, they are also out earlier, and a few hundred mason bees can do more pollinating in a fruit orchard than thousands of honey bees, if honey bees were active so early (which they are usually not). Mason bees will feed from whatever nectar is available, so as a gardener it is a good idea to have a wide variety of "nectaries" blooming from the very beginning of the season, so that female lignaria have something to eat while they are waiting for fruit trees to blossom. Like mason bees, flowers do more than look pretty.

Providing Nesting Sites for Mason Bees

It is relatively easy to provide nesting sites for mason bees, and one can make or purchase a variety of mason bee "houses" which basically mimic a condominium of hollow straws. Wooden blocks or dead limbs can be drilled with holes 5/16" wide and about 6" deep, or bundles of straw and bamboo can be placed horizontally under an overhang where they will be sheltered against rain and cold winds.

The mason bee itself is a remarkable creature, but not necessarily a great looker. With their hairy bodies and blue color, mason bees may look more like flies than bees to some people. One of the distinctive things about them is the presence of five eyes. Yes. Five. In addition to the two large "compound eyes" we recognize, each lignaria also has three much smaller dot eyes on its forehead, used for horizontal alignment in flight. Pretty cool, eh?

For Further Information

• Wikipedia has articles on Megachilidae, mason bees generally, Osmia lignaria and carpenter bees
• Local expert Sherian Wright has a terrific website at MountainBugs.com
• WSU and British Columbia have web pages about mason bees
• Sherian Wright has several plans for mason bee homes one can build