Just as I was sitting down to write my weekly blog post, my cousin sent me an email. She had received a bug-related item as a gift, and wanted to know more about it. Let’s take a look:

(Photograph by Karen Gibson, used with permission)

Any idea what this is?

I’ll give you a hint.

(Public domain image of Osmia lignaria from USGS Bee Inventory and Monitoring Lab Flickr Photostream)

This small bee is an blue orchard mason bee. It gets the name “blue” for its metallic blue-black color. The “orchard” part is because it is a significant pollinator of crops grown in orchards, such as cherries, apples, plums, and almonds. This bee and its relatives are called “mason bees” because they use mud in their nests, plastering it on like a human mason sticks together bricks with mortar.

Do you see all the pollen in the hairs on the underside of the bee’s abdomen? Having large pollen collection areas, combined with the fact the mason bees visit more flowers per minute than other types of bees, is what makes them such good pollinators. In fact, just a few orchard mason bees can pollinate the same number of fruit trees as thousands of honey bees.

Back to my cousin’s gift. Unlike carpenter bees, mason bees do not excavate nest holes in wood. Instead, they must find beetle galleries in tree trunks to serve as homes for their larvae. Nest holes may be in short supply in places where old tree trunks are removed right away. To help mason bees survive, you can provide a bee house like the one my cousin received. It is the insect equivalent of a bird house.

Building and Hanging an Mason Bee House

If you want to build a mason bee house, drill a series of holes 5/16 to 3/8   inches in diameter (smaller diameter holes may be used by leafcutter bees) six inches deep in pine or fir wood. Space the holes about 3/4 inch apart, the number and design are up to you. Paint and decorate as you wish. Mount the house firmly to fixed surface such as a wall or tree (the bees don’t like their nest to swing). Place it where the house will receive early morning sun. These bees are usually active in the spring.

Do not rest the house on the ground, where ants and other crawling insects can get inside.

When a female mason bee finds the bee house, she will gather pollen and nectar into a ball called “bee bread” and put it deep within one of the tunnels. She will lay a single egg on the clump and close up a short chamber by plugging it with mud. Inside the chamber the egg will hatch into a larva, which will feed on the food its mother provided. In a short time it will complete development and turn into a pupa, and then finally an adult bee.

The female bee creates several similar chambers in a row within a single tunnel. You can see the inside of a nest about half way down this USDA page. When she is finished, she will cap the end with a plug of mud, a signal the nest is occupied.

(Public domain photograph of Osmia ribifloris by Jack Dykinga of the USDA.)

Depending on where you live, you might not attract the blue orchard mason bee, Osmia lignaria, to your bee house. There are roughly 500 species of Osmia around the world, however, so you may provide a nest for a related species that pollinates your local plants. For example, the Osmia ribifloris in this photograph is an important pollinator of blueberries.

If she doesn’t mind, maybe Karen can send us an update later in the year letting us know if any bees found the house.

Please leave a comment if you have any questions about mason bees or bee houses.