Simple Plan for Mason Bee Houses

Mason bees are nice little native pollinators that are easy to attract and support in your yard.  Like most bees, they're solitary, meaning they don't have a hive with queens and workers and all that, and they don't sting because the don't have a hive to defend.  They gather pollen to lay eggs on, to feed the next generation, but they aren't very efficient at it, which means they have to visit lots of flowers, which makes them excellent pollinators.  One species, Osmia lignaria, comes out fairly early in the spring, does it's thing, and then disappears for nine months until the next spring.  Because of their timing, they're excellent pollinators for many fruit trees, like apples, pears, and cherries, that are flowering when the bees are flying.  Thus their common name of Orchard Mason Bee, and the reason they're a favorite commercial supplement for European Honey Bees.

Where they disappear to is no mystery.  The adults pack pollen into beetle holes in wood or hollow twigs or other natural cavities, lay eggs on the pollen stores, seal the holes with mud and then die.  The eggs hatch and the bees complete most of their life cycle inside, only coming out for the mating, pollen-gathering, and egg-laying phase in the spring.  This is where this plan comes in.

It's easy to provide a home for these little guys, either for the fun of watching them do their thing, or because you have fruit trees, or because you want to help the little critters of nature out of the goodness of your little hippie heart.  Basically, you take a piece of wood and drill a bunch of holes in it.  They like holes in the 1/4" to 3/8" range, with 5/16" being published as optimal.  Commercial houses pack hundreds of paper straws into small holders, but this kind of density invites pests and diseases, and pretty much requires "harvesting" the bees in the fall instead of just letting the bees take care of themselves.  Put twenty holes in a block of wood and call it good.  If you want more, build a few more houses and put them in different parts of your yard.

Here's the first house I built, several years ago.  It's a couple of old Douglas Fir 2x4's from my house, drilled and then glued together.  The holes are about 3" deep, and 1/4" in diameter.  I cut the top off at an angle and glued on a piece of cedar fencing material to keep the rain off the top, and it hangs on the east-facing side of my shed.  I drilled a shallow hole in the back, angled up, which hangs nicely on a 10d finish nail hammered in at an angle.

simple mason bee nesting house

Fast forward a few years, and this house has been used and re-used by several generations.  It's now early March, and I expect this year's bees to dig out of their nest holes and start flying around any day now.  What I'd like to do is hang up a new house, and have them use it so I can clean this one out and get rid of all the junk that's plugging up some of the holes.  The problem is, if I leave it up, the bees will build nests in it again.  The solution is to cover the house with a box that hides the holes.  There's an exit at the bottom for emerging bees to escape, but they won't come back and use it as a nesting area.