The information contained in these web pages has not been verified for correctness. Some of the information contained herein is hearsay and may not be correct. Use the information from these pages only at your own risk!

What Are They?

Orchard mason bees are native North American bees. They live all across the United States and Southern Canada, but are particularly common in the Pacific Northwest, especially in the Puget Sound area and western Cascade Mountains. They are also called "blue orchard bees" and scientists know them as Osmia lignaria. They are beautiful insects, about 1/3 inch long and blue black with a metallic sheen. Unfortunately, they are sometimes mistaken for large flies (look closely - they have 2 pairs of wings and are not interested in garbage!). The females are somewhat larger than the males and the males have a white hairy face. Like all bees, mason bees collect flower pollen as a protein source for their young and get their energy from flower nectar. In shopping for groceries, they carry pollen from flower to flower, achieving pollination.

A number of things set mason bees apart from other bees:

The above features make orchard mason bees the perfect pollinator for those who have a small number of fruit trees, but may not want to manage honey bee hives. They are also a fascinating wild creature that can be easily encouraged to colonize the backyard garden environment, to the benefit of the gardener, orchardist, homeowner, and nature lover. Mason bees are totally safe, even around children and pets.


Female mason bees make their nests in hollow cavities. In nature, these are found in the fissured bark of trees or in the emergence holes of tree-eating grubs. Mason bees can be attracted to you yard. They may already be in your neighborhood, especially if you live in the Puget Sound region. To make mason bees a part of your home life, simply provide them with nest holes and make sure they have plenty of flowers to feed on. The ideal nest hole is 5/16 to 11/32 inches in diameter and 4 to 8 inches deep. The bees will nest in a wide variety of such cavities. Straws and holes drilled in boards are commonly used. But to produce happy and healthy bees and to avoid disease build-up, you should give the bees quality housing.


Orchard mason bees have problems, just like all creatures. They have certain requirements in nest placement, preferring a warm, dry situation. They must have adequate flowers to raise their brood. And finally, they are subject to diseases, parasites, and predators. These include fungal diseases of the developing bees, various types of mites, which compete with the larval bees for foodor parasitize them, and predatory insects or larger predatory animals like woodpeckers. The most serious of these problems are the diseases and parasites.

Straw Systems

Bare wood holes are acceptable to mason bees, but over time the become fouled with debris and germs. If not cleaned, the hole loses its attractiveness as a subsequent nest cavity. Mason bees tend to "go away" from such nest blocks after the first year or two. Diseases and parasites may build up in unhygenic nest blocks. The best nest system for orchard bees is a smooth wood hole with a porous insert or liner (straw) which can be replaced each season.

The concept of straw inserts was developed by USDA scientists in studying mason bees. With a straw system, the filled nests can be removed in the fall, and replaced with new inserts in the spring. The new bees in the nests can be safely stored in a cool environment until it is time for them to begin the nesting cycle and pollinate. Then, simply place the nests near the nest blocks and allow the bees to emerge and re-nest in the new inserts.

Related web pages:

Commercial suppliers:

Electronic mailing lists:

Suggested references:

If you are interested in any of the titles below, click on the title and it will take you to Amazon.com for ordering. Click on the icon at the left for more information.


This page was last updated on December 09, 2007