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Mason Bees in My Garden

Mason Bees in My Garden

By now, if you’re a gardener, you’ve read about those industrious little orchard mason bees (Osmia lignaria). Native, wild bees—like the mason bee—don’t live in hives and they don’t make honey. They pretty much do only one thing, and they do it exceptionally well. They pollinate fruiting trees and plants.

Closeup of mason bee.
Photo credit: Wikipedia/Red58bill – some rights reserved

In fact, according to Crown Bee (Crown Bees Website) one single mason can do the work of 60 honeybees! There are lots of reasons to love mason bees. Because they don’t make hives, they aren’t territorial. And that means that they rarely sting. Both males and females are very docile, and the males don’t even have stingers.

Messy is Good

It turns out that mason bees are also more likely to pollinate your crops than honeybees, because (quite frankly) they are messier about collecting pollen. Instead of the neat little sacs that a honeybee carries on its hind legs, mason bees carry pollen on their furry stomachs. And while mason bees do a great job of collecting pollen for their own uses, they also manage to deposit quite a bit of pollen on each subsequent flower that they visit.

Here in Oregon mason bees are especially useful because they are active early in the growing season when fruit trees like plums and apples are flowering. And unlike honey bees they don’t mind cool, damp weather. But be warned, really cold temperatures and heavy rain will discourage even these stalwart pollinators from visiting your garden.

Mason bees are great for home gardeners because they have very few demands. All they really need are plants that bloom throughout the growing season and a good nesting site. Notice that I said “nest” not “hive”. That’s important, because creating a desirable nesting site is the best way to attract mason bees to your garden.

Building a Mason Bee Box

A Mason Bee HouseBy now, you’re probably convinced that you want mason bees in your garden. If so, read on for step-by-step instructions.

Mason bees are solitary creatures. But even though they don’t live in a social hive, they don’t mind nesting close to other bees. A female typically looks for holes in wood that are 5/16” in diameter. She will lay an egg in the back of the hole, pack in some food and seal the chamber with mud. That first egg is always a female. Mama will continue laying eggs in the hole, adding pollen and sealing each chamber until the entire hole is filled. All of the eggs after that very first one will be male mason bees. It’s kind of amazing when you think about it.

Mason bees don’t excavate their own holes, so your job is to provide a hunk of wood with right-sized holes drilled into it. But there are other niceties you should observe, like protecting the nesting site from rain. Or making sure that a nice mud puddle is nearby. I promised you a step-by-step list, so here it is!

  1. Find or buy a block of untreated lumber. It’s important for the wood to be free of preservatives or pesticides. Chemicals are bad!
  2. Make sure that the wood is large enough to accommodate multiple holes. There is no rule about the size of the wood you use. Just remember that you need a hunk of wood that can accommodate a hole that is anywhere from 3” to 5” deep. A 4” x 4” post will work, as will an old log.
  3. Drill a series of holes, where each hole is 5/16” in diameter and 3-5” deep. For example, in a 4” thick post, you’d want to drill the holes 3 ½” deep. Don’t drill through the entire piece of wood. Each nest should have a solid back.
  4. Place an overhanging “roof” on your bee box to prevent rain from entering the nests.
  5. Mount the bee box on a south or southeast facing wall or fence, making sure the box is securely attached.
  6. When choosing your location make sure that there is a convenient source of mud nearby and that there are (or will be) flowering plants within 100 yards of the nest.

But Did the Bees Like the Critter Condo?

I’ve included a picture of the mason bee box (above) that I built (with hubby’s help) for my own yard. I made a few modifications to the basic design that is described above, which I’ll run through here.

First and foremost, I decided to use smaller blocks of wood, mostly because we had a ton of 2 x 6 lumber left over from another project. Instead of mounting the blocks directly to a fence post, we built a “house” for the blocks. As you can see from the photo our bee house is divided into three sections and can accommodate a number of wood blocks.

In retrospect, this was a stroke of genius, because it allows me to discard old used blocks and to easily install new clean blocks each season. Using clean wood each season guarantees that I won’t be subjecting my mason bees to parasites or disease.

This was my first attempt at a mason bee box. And to be honest, my results were mixed. I thought I’d have dozens of bees lining up to live in my little critter condo. But the truth is that only about a dozen mason bees decided to take up residence. My hope is that over time the descendants of these bees will build nests of their own and grow my little community of native pollinators.

Nature Loves Diversity

During the mason bee “season” I checked on my bee box everyday to see how many more bees had built nests. Mason bees are typically active here in Portland in March, April and May. So by June, I was pretty much ignoring my bee box.

In July, I noticed several brand new nests in my bee box. But unlike the gray mud that a mason bee uses to build its nests, these holes are bright green and bright red. Here’s a photo.

Mason Bee BoxClearly, some other creature had decided that my bee box would make an excellent nesting site! If you have an idea what might be gestating in these other nests, please leave a comment below. I’m doing some research myself, and have contacted a few groups that specialize in mason bees and insect IDs. I’m hoping to have a good guess about my latest bee box inhabitants before spring rolls around again.

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