mason bees

Putting the squeeze on mason bees

Talk about claustrophobia. Just looking at this bee gives me the heebie-jeebies. Conventional wisdom says a blue orchard mason bee (Osmia lignaria) likes a 5/16th-inch nesting hole. This hole is smaller, only 1/4 inch, drilled specifically for leafcutters. Apparently, no one in the bee world is reading my mind because the masons are eschewing the larger holes in favor of a tight fit. They remind me of women struggling into small garments—just hold your breath and sque-e-e-e-eze.

Even though they give me confined-space anxiety, I love to watch these workaholic bees. Returning from a foraging trip, the females look like big black flies with one exception: the undersides of their abdomens are painted with colorful pollen. The bees crawl into their holes head first, back legs flailing for purchase against the sides of the tunnel. After a few moments, they back out, do a quick 180, then re-enter tail-end first.

Mason bees make odd little noises while they work. Sounding a lot like bugs in glass jar, they make vibrate-y, echo-y noises that sound like distress . . . and maybe it is. Panic attacks?

When they’re not carrying pollen, the bees haul in the mud they will use to seal up each compartment until the nest is complete.

My worst mason bee problem occurs each year right here at my desk, which is near a double-paned window in a white vinyl frame. On the outside of the house the frame has two little drain holes. Every year the mason bees go into those holes and build nests. From the inside of the house I can’t see any opening at all, but somehow the bees hatch to the inside. Sometimes I find them on the windowsill or sometimes they get caught between the window and the screen. I’ve rescued five so far this year, and a sixth I found dead on the carpet.

The other odd thing has to do with pollen mites. One year I purchased mason bees from a place in Oregon and for the next two years had serious pollen mites. I never purchased bees after that. Instead, I just built housing and let the wild masons move in. Since then, I’ve seen no mites. Each afternoon I net as many bees as I can and check for mites, but for three years now, I’ve come up clean. I’m wondering if local populations have local resistance. Perhaps shipping them around the countryside is the wrong thing to do—it certainly didn’t help the honey bees or the bumble bees. Serious food for thought.



  • Panic attacks? You’re anthropomorphizing your claustrophobia Rusty.

    We had left out a tarp over the winter last year and when I went to fold it in the spring, I found these plugs of pollen and live bees that apparently had made a nest in the folds of the tarp!
    Now this spring I’ve found these very small fuzzy bee-looking insects, very petite and not blue mason bees. I find them resting on the leaves of my citrus when I put it out to get some sun- they look like miniature honeybees. If I can get a good picture I’ll send it to you, I can’t seem to figure out what they are.

  • Brainstorm! I think it’s a leafcutter bee. I just remembered seeing the leaves had been chewed/cut and wondering what could be doing that so early in the season. Then your mention of leafcutter bees and how small the brood holes are…lo and behold, the lightbulb went off and pictures confirmed it.

    I love your blog Rusty, thank you for sharing so much information with your readers.

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