Mason bee condos

Mason bees (Osmia spp.) are mostly-native, solitary bees that actively forage for nectar and pollen during a few brief weeks in April and May here in Southeastern Pennsylvania. The adults began emerging this week during the few warm, dry days that interrupted our cool spring weather.

Overviews of the mason bees’ life cycle and habits can be found here and here.

Since the bees require tunnels for nesting but can’t excavate their own nests the way carpenter bees do, you can attract them to your garden by providing nesting blocks, bundles of bamboo, or commercially-available cardboard or paper tubes. The holes should be sized as close to 5/16 of an inch as possible. Since next year’s bees will be developing inside the tunnels for an entire year, it’s best to place the nesting block or bundle in a location protected from excessive rain or snow, such as under a porch roof.


I made several rustic wood nesting blocks like this one last year. Note that I drilled a few larger holes in the forth row down, but the bees didn’t occupy those tunnels. I purchased the plastic cylinder with empty cardboard tubes, and the mud “plugs” indicate that nesting females completely filled those tunnels with eggs last year. The adult bees will emerge over the next couple of weeks!


If you’re a creative type, you can already imagine the wide variety of mason bee nest structures that would provide the basic requirement of dry, 5/16-inch diameter tunnels. My friend Keith Snyder has elevated mason-bee home construction to an art form, as proven by his latest creation shown below (which I was lucky enough to receive as an early birthday gift this year!).


Keith prefers to use natural and reclaimed materials. He built the wooden frame of this bee condo with scrap wood, painted it green, and filled the compartments with Phragmites stems (yes, the invasive wetland plant!) and rolled-up, dried southern magnolia leaves. Keith picks up vintage costume-jewelry bees in his flea-market travels and often adds one as a decorative touch.

In a couple weeks, dozens of recently-emerged and mated female bees should be busy laying eggs in these tubes. I’ll try to post photos!