Mason Bee Bonanza

Three days ago I got to witness something I hadn't seen before:  the mason bees awoke from their winter's inactivity and emerged to enjoy the spring weather.  The air around the house we had put up was filled with gentle little bees, checking out the fresh air and freedom.

If you look closely, you'll see a black dot to the right of the wire the house is hanging from - that's a mason bee flying.  There's a second one down in the center, near the bottom, checking out one of the tubes....

A few seconds after I took this shot, I took another.  The bee by the wire had landed and I got a photo of it, albeit a rather blurry one!

Our mason bee house is from Gardener's Supply.  A dear friend gave it to us and we've had it up for 2 years now.  In fact, this house attracted mason bees the very first year we put it up.  I've rarely seen the bees, though - just the mud they use to seal their nest cells when the tube is full.


When we first put up the house, Greg thought we should order mason bees to be sure there were some to start up a population.  I was hoping that our landscape had enough healthy, natural habitat for us to attract mason bees that were already here.  With bugguide.net saying that there were 150 species "in our area" (presumably the continental U.S.), I was hoping we could attract native species, rather than introduce a species that might not belong here.

In this case, it turns out that I was right.  While we've never been even close to 100% occupancy, our bee house has definitely become a home.

Not wanting to bother the bees too much, I didn't push to try to get a great shot.  I stayed back quite a ways and let my lens take me in closer.  Now, as I'm attempting to share this on my blog, I'm wishing I'd tried harder to get at least one good closeup.

The reading I've done on mason bees says that the outer sections of the tubes have males that develop in them, while the females develop in the deeper cells - the female mason bee can apparently determine the sex of the offspring that will emerge from her eggs.  This makes sense in several ways, biologically.  First, any predation by woodpeckers will take out males, rather than females.  Since the mason bees aren't monogamous, the males that remain can fertilize more than one female, ensuring another generation. 

Secondly, this causes the males to hatch/break out first.  They stay around the nest, waiting for newly emerging females and mating with them as soon as they emerge.  Another biological strategy for ensuring the continuation of the species.

If you look closely at the photo below, there are 2 mason bees, one in the lower left-hand corner, exploring the openings to several tubes, and one in the upper right-hand corner, coming out of a tube.

Once the males have mated, they apparently die.  Each female lays her own eggs and provisions them so they can develop properly.  First, the female makes a mud plug in the back of a tube and begins collecting pollen and nectar, depositing it inside the tube she's plugged.  When there is enough food to fully support a developing larva, the female lays an egg on the pollen mass, then seals that cell with a thin wall of mud.  There are generally 5 to 10 cells in each tube, depending on the length of the tube.  The final, outermost cell gets a thick layer of mud capping it, for protection from predators.  A female is able to lay, and appropriately provision, only 1 to 2 eggs each day.  She lives about 4 weeks.

Away from human-provided bee houses, mason bees use tunnels made by wood-eating beetles or they use hollow plant stems.

As with all solitary bees and wasps, the females will not sting unless actually handled roughly or trapped, for example between clothing and skin.  Once the female stings, she dies and is unable to lay more eggs, so there is no biological incentive for her to be aggressive.

Mason bees and other solitary bees are excellent pollinators.  If you haven't added a bee house to your yard, why don't you give it a try?