PHOTO: Tessa Zundel

May 2, 2016

Giving mom flowers on Mother’s Day is great, but what if you gave her a little something extra to go with that bouquet Moms love flowers, but so do bees—and bees make the garden and the world a happy, healthy place by pollinating so many of our food crops. This year, make mom a mason bee house to encourage these small, effective pollinators to visit your garden that may already be full of the floral offerings of Mother’s Days past.



What Is A Mason Bee?

From the genus Osmia, of the family Megachilidae, mason bees are usually black or metallic blue-green, though sometimes very brightly colored. Mason bees range in size but are typically about half the size of a honey bee, and they don’t sting, so they’re an uncomplicated beneficial insect to invite into the garden. (Well, the males don’t sting and the females rarely do and only under extreme duress.) They’re efficient pollinators in the garden and orchard, even considered to be more efficient than honey bees.

If you want to simply encourage mason bees and other pollinators in your garden, you can do so by planting pollinator-friendly plants. Having as close to a year-round food source for pollinators (pollen and nectar producing plants like flowers and herbs) will be of enormous benefit to the bees and butterflies.

Providing A Mason Bee House

If you’d like mason bees to be present in your garden in the largest numbers possible, thereby providing the maximum amount of pollination for your orchard and garden, you can also create nesting sites for them.

From what I’ve researched, providing mason bee houses doesn’t necessarily increase the numbers of mason bees in your area permanently. Being solitary bees, they don’t have honey bees’ homing instinct, which tells them to return back to a colonized hive. This can make them flighty guests in your garden, because they don’t necessarily return to nest in the place they were hatched.

However, with proper maintenance, providing mason bee houses shouldn’t harm their populations and could even increase the population within the first two years that you place the houses in your garden. It’s important that you remove or thoroughly clean your mason bee houses every two years to avoid pathogen build up and even mold, especially if you live in a humid area.

Mason bees most often nest in wood, using holes created by other insects and birds or even old nails; they don’t drill into wood themselves. Filling the holes with mud to make them safe and snug for laying eggs, mason bees will need a small patch of exposed dirt in your yard if you’d like them to nest successfully in your garden. Sometimes people worry about them causing damage to their homes by nesting in existing holes and cracks, but they don’t cause any damage while nesting.

Here are some tips for getting the mason bee house hung just right:

Place it in a very sunny, southeast facing position, protected from wind and in the shade, especially if you have warm springs and summers.

Hang the mason bee house 3 to 5 feet off the ground to avoid splash up when it rains.

Provide some kind of roof to prevent water from getting into the nesting site and causing mold. The mason bee house pictured here is under the cover of a porch roof, so this one doesn’t have its own covering, though the ones we’ve set out on the fence do.)

Cover your mason bee house with hardware cloth to protect the larvae from birds. Most birds won’t be able to reach the larvae if you’ve drilled deep enough (at last 5 to 6 inches), but flickers can be especially determined, and woodpeckers have very long tongues.

Options For Making Your Own Mason Bee House

You can make a mason bee house out of paper straws (never use plastic) by following these instructions from Louis County Beekeepers. These straws can be bundled together and inserted into a coffee can or even into the nesting block featured below. They’re not the sturdiest option, but with the right cover, the bees will enjoy using them.

The other kind of house you can make requires a 6- to 8-inch-long block of wood. One design, which is nicely detailed in Pollination with Mason Bees (Beediverse, 2009) by Dr. Margriet Dogterom, is really two trays with channels cut out with a table saw for the bees to nest in. One tray is inverted and stacked onto the other so that the channels line up, creating a cozy corridor in which baby mason bees can develop. As Dr. Dogterom points out:

“The biggest advantage of trays is that they can be dismantled and examined … The tray system allows for the removal of predators and parasites and increases your bee population, higher than is normally observed in nature.”

Our Mason Bee House

We still haven’t unpacked our table saw from our recent move, but we knew where the drill was so we made the other kind of wooden mason bee house that is commonly seen. Using the 6- to 8-inch block of wood, we drilled holes 6 inches deep into the block. You can use any untreated block of wood (except cedar, which naturally repels insects) and a 5/16-inch drill bit—that seems to be the size hole that mason bees favor most. You can use a template to evenly space the holes if you’d like, but the mason bees really don’t care either way.

What You’ll Need:

Block of untreated wood 6- to 8-inches long

drill with 5/16-inch drill bit

drill press

water-resistant paper (optional)

scrap wood for roof structure or a larger container to insert the bee house into

hardware cloth

staple gun

L brackets or pipe strap

Step 1

Using a drill press with a 5/16-inch drill bit, drill the initial holes up the length of your wood block, just as deep as it will go. This will get you started with the holes and make it easier to get uniform coverage and make it easier for you to use your cordless drill to finish off the job. If you don’t have a drill press, you can use a cordless drill to drill all the holes. The drill press just enables you to set up completely straight holes; with a cordless drill, you run the risk of going even slightly sideways and possibly drilling into another bee tunnel. If you don’t have a drill press, don’t sweat it and just keep your holes farther apart to avoid crossing them over by accident. Either way, put no more than 25 holes in any one house (to avoid confusing the bees), and stagger them around the block.

Step 2

Using the cordless drill with 5/16-inch paddle bit, finish off holes so that they’re at least 6 inches deep—longer is OK. Use a piece of electrical tape on the drill bit to mark how deep you want to go into the block. If you happen to drill to the back, just be sure to add a back piece so the bees are protected. The male bee larvae are laid at the front, and the females are laid at the back. Drilling deep nesting tubes protects the larvae from birds and the elements, making it more likely that the boys make it out alive to mate with the girls in the spring.

Step 3

After you’re done drilling, carefully bang out any leftover sawdust.

Step 4 (Optional)

Using the paper tube instructions linked above, insert paper straws into your holes so that you can remove them thereby more easily sanitizing your bee house. If you chose to do this, plan to carefully remove your tubes in the fall, placing the enclosed larvae in a safe place, such as a lidded bucket with a single hole drilled into it. When they hatch, the bees will exit through the hole.

You can insert new straws into your mason bee house in late winter/early spring and begin the process over again with clean tubes. In humid areas, this may not be effective, as mold can develop on the tubes, requiring that you not reuse the house.

Step 5

Paint or draw a design near the entrance of at least half of the holes to help the bees orient themselves. The less time mason bees spend trying to “remember where they parked,” the more time they can spend pollinating. Dr. Dogterom explains:

“Decorating the front of the nest makes it easier for bees to find their own nesting tunnel. A nest can be decorated with simple designs and or with one or two colors. Too few or too many markers at the nest will confuse the bees. Bees that are confused by the markers or lack of markers close to their nest can be observed flying in and out of several nesting tunnels or getting thrown out of neighbors’ nesting tunnels.”

Dr. Dogterom suggests using yellow, mauve, pink and blue colors but not to make them too fancy or complex. Simple letter shapes like X, V or O will do nicely.

Step 6

Using a staple gun, fit your hardware cloth over the front of the mason bee house, slightly curved outward about 1 inch off the surface to prevent long-beaked birds from eating your precious mason bee larvae.

Step 7

Hang the mason bee house on an obliging post or fence with an L bracket or pipe strap. We used a pipe strap to avoid puncturing the bee house further.

Step 8

It’s important to keep your drilled-house clean. If you use the straws, follow the instructions in step 3. If you don’t, plan to put your whole mason bee house into a lidded bucket or box in the fall with a single hole drilled into it so the bees can escape when they’re hatched.

Dr. Dogterom suggests making sure that the box is painted dark, because the bees will be less likely to return to it if it’s not brightly lit. After the bees have hatched, which can sometimes take two years, you can just burn the wood. The biggest drawback to this design is that you really can’t clean them. However, the bees do seem to like them and use them well, and they make a wonderful family project. Watching the bees set up during the year and emerge in the spring is truly a joy.