February, 1998

The Orchard Mason bee can be an effective pollinator

by Carl Cantaluppi

North Carolina State University

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 or 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.

Nest construction

The native eastern species of Orchard Mason bee will nest in holes drilled in a wooden block. Untreated four- by six-inch lumber works great. Holes can be drilled in the wood on 3/4-inch centers. They should be four to eight inches deep (depending upon the size lumber used), smooth, and a 5/16-inch diameter hole is important. A smaller hole encourages higher production of male bees which reduces the reproductive potential of the population.

Blocks may be drilled from either face, giving shallower or deeper holes. Do not drill completely through the lumber. Drill the hole to a depth about 1/2 inch from the back of the block. Attach a roof to provide protection from the midday sun and rain. Outside surfaces may be painted or stained, but do not use wood preservatives. One hole may be drilled in the back to provide a means of hanging the block. Face nesting blocks as close to the southeast direction as possible to catch morning sun and affix it firmly so that it does not sway in the wind. It should be located at least three feet above the ground.

These bees need mud to construct cell partitions, so adding a mud supply may be helpful. This can be a trench or tub located nearby where muddy soil is maintained during the nesting period. The mud should not be highly organic or sandy. Clay soils work well.

Do not move the blocks during the weeks of active nesting. Once all nesting activity has stopped, the nesting block may be moved to a shelter such as a shed or unheated garage. Be gentle when moving occupied blocks at this time of year. This will give the bees added protection from predators and parasites, yet will allow them exposure to the cold temperatures that they need to break hibernation. If desired, bee emergence can be delayed for a short period by refrigerating the block in the spring until you are ready for the bees to emerge. Bees will need three days to warm up following refrigeration.

The above article was adapted from the following publications:

· "Orchard Mason Bees," Washington State University King County Cooperative Extension publication 156 by Ron Bekey, former research assistant now at Oregon State University, and E.C. Klostermeyer, former entomologist, WSU.

"How To Raise and Manage Orchard Mason Bees For the Home Garden" by Stephen Bambara and James R. Baker, Extension entomologists, "Ornamental and Turf Insect Note 109," Department of Entomology, North Carolina State University.