Our native bees are extremely important pollinators and often forgotten about! Habitat loss and insecticide usage (including mosquito spraying) are particularly detrimental to these populations and they're disappearing fast.

Cut out the pesticides first, then boost your garden's productivity by providing a happy nesting site for solitary bees. Slightly smaller than honeybees, mason bees are peaceful and amazing pollinators visiting as many as 1000 blooms per day. Females lay eggs in the hollow tubes and seal them up with some mud. Other beneficial insects including wasps and leaf cutter bees may also take up residence.

Choose a sunny and permanent location by early spring and these bee houses can help extend their habitats.

Other great ways to help our insect friends is to plant large blocks of flowers and choose native plants that have a succession of blooms through the seasons.

Step 1: Materials

Materials:

1X6X8 untreated pine
1X4X8 untreated pine
Finish Nailer and 1 1/4" Nails
Wood Filler
Paint
Things with small holes in them

Tools:

Tape Measure
Miter Saw
Straight Edge
Pneumatic Finish Nailer
Sander
Putty Knife

... You could get by without the nail gun but it certainly makes things lots faster.

Step 2: Cut the Wood

In the picture, I've included some dimensions OR see below.

Side Walls: (2)

On your piece of 1X6, measure and mark 12" and cut directly from your 1X6X8 Board with a miter saw at 5 degrees. The resulting piece should have a side that's 12" and the other less than that (maybe 11.5"ish, the 5 degree cut will determine that height). This angle gives just enough pitch to the roof to shed water.

Since you cut directly from the 1X6X8 board, it too will have an edge that's cut at 5 degrees already so you can now adjust your saw for 90 degree cuts again. Measure 12" from the tall edge and cut the second piece. You'll end up with both walls and saves you from an extra cut and wasting a bit of wood.

Top (1)

From the 1X6, measure and cut a 6" piece on the saw at 90 degrees.

NOTE...You could think about that 5 degree cut you did for the walls and cut this piece so it's flush with the walls. I used to do it but it's hardly noticeable and you'll save a bit of time with straight cuts.

Back Piece(1)

On the 1X4X8, Measure 11 3/4" and cut with miter at 90 degrees. We want this piece to be a bit shorter than the tall end of the side walls to keep assembly easy.

NOTE... If you try to get the back and roof to fit perfectly together, you'll need to consider that 5 degree cut you made earlier. If it's just a hair taller than the side walls your roof won't fit flush or the floor won't. Both outcomes are bad and you probably won't realize this until your bee box is half assembled. The lesson here is just cut it a little short and move on with your life.

Bottom and Shelves (3)

On the 1X4, measure 4.5" pieces and cut them at 90 degrees. These 3 pieces are the same.

NOTE...If you'll be making several houses at once. It helps to make a reference mark directly on your miter saw guide so you don't need to keep measuring.

Step 3: Assembly

Now that your wood is cut, it's time for assembly with the pneumatic nailer.

I use 16 gauge finish nails that are 1 1/4" long.

Before assembly check out your shelf pieces and sand smooth any rough edges on the one side that will be facing outwards. It's easiest to do this now since they'll be slightly inset after assembly. You might as well wait to do the rest of the sanding until later.

Assembly

First nail the back wall and the sides together making sure the bottoms are flush. I stick 3 nails in each wall and they hold together just fine. If done correctly, the top of your back wall should be just a little lower than the side walls.
Nail the bottom shelf flush with the other pieces. (I stick 2 nails though each of the side walls and one through the back.
Make a pencil mark on the front edge of the box, lines that are 4" and 8" from the bottom of the box. These lines are where the tops of the shelves should line up with. Push the shelves into place, making sure the lines match up and the box compartments look like they're in square. After the box portion is complete, I stick some 2X4 pieces with drilled holes in the top section and these measurements make sure there's room enough for those. If you plan for a different fill arrangement, go wild with your shelf spacing.
Go ahead and nail the shelves into place through the walls. 2 nails per side.
TIP: If you're making several, it helps to make pencil markings were the 4" and 8" lines are on one of your extra back walls. This way, you can hold it up to the front of the box and quickly see where all 4 marks go on your bee house.
With the box flat on its back, stick the top in place and by eye, get it so its equally overhanging the left and right side of the box. Because of the 5 degree cut we did earlier, this piece won't sit flush with the table you're assembling it on but that's just fine. Nail into place with 4 finish nails into the wall pieces.

Step 4: Fill the Nail Holes Then Sand Box Smooth

Fill the brad holes with sandable wood filler. If it's water based, I like to thin my filler just a little with some water to make spreading and filling in holes a lot faster. Let dry and then sand smooth along with any other rough edges on the box.

Because of the slight differences in the stock wood and also your cutting skills, some of the shelves may not sit exactly flush with the box and gaps may appear. If they're minor, the paint job and inner components will make it hardly noticeable. If you really mind the gap, go ahead and get a tube of painters caulk and go wild. Don't forgot to smooth it out with a wet rag and some water because once it dries, there's no changing it.

Step 5: Paint

After your box is smooth and sanded, It's time to paint. Color choice is up to you.

Because we use untreated wood (so bees don't need to be around chemicals) I like to use the best quality exterior paint. A little quart will paint many many houses and the 2 coats it takes for the paint job to look professional are all you need. (no primer)

When painting, you don't need to paint any farther than an inch or so inside the box. The bamboo and other box innards would block the paint job anyways so forget about it.

Step 6: Drill a Hanging Hole

Because we were careful and made the bottom all flush, you can stick your mason bee house on a table top but it's also really nice to have the option to hang it up. Drill a hole (big enough to accommodate a nail) directly through the back about an inch below the top.

The guts of your box will obscure the hole you just drilled in your back wall.

...In this picture, you can also see the purposeful gap we left in the back piece of wood.

Step 7: Fill the Box

Mason bees are small cavity nesting bees. They'll find pre-existing holes to lay eggs in so really anything that's breathable with varying hole diameters of 5/16" or less works perfect.

Any bigger and the bees won't use the holes.

As you vary your holes sizes in a decreasing diameter, you start catering to a different species of native bees. This is a great thing to do. Bamboo is a great option because there are lots of different diameters already without a ton of drilling on your part.

It's important to have your cavities as deep as possible too and your box depth is (4.5"). The reason for this is bees lay multiple eggs in each tube. The depth of the tube determines how many eggs will be laid and also what sex they'll be (based on position in the tube.... males are closer to the front)

I like to use 2X4 chunks cut at 4.5" and then drilled with lots of holes. For drilling the holes, an auger bit is far better than a spade bit, forstner bit, or standard drill bit in terms of staying sharp and ease of drilling.

We put the top shelf at a height to cater for 2 2x4's stacked on each other. Keep in mind if you go this route, the 2X4's will probably just barely not fit between the walls. I usually need to plane them down a hair so they fit perfectly.

Finally, I like to add wood chunks, pine straw, or hay to one of the compartments too. This isn't an area for the solitary bees to nest in but can provide a safe space for lots of other beneficial critters to crawl into and hang out.

There's lots of other options to fill it in so be creative.

Step 8: Hang It

When you're ready to hang the box, choose a spot that gets some nice morning sun. When the native bees start to nest, they'll overnight in their unfinished tubes and the warm sun in the morning gets their day started earlier.

Depending on where you are in the world, native bee species have life cycles that work with the seasons. Sometimes adults are active and other times the species will only exist in egg form. Moving your boxes after you start to see activity will confuse the mom bees so don't do it.

Finally, since we're catering to native bees and not stocking these houses, sometime's it takes awhile for them to find your new house. Sometimes, the populations are so decimated you won't see any... As long as you have one up though, if a bee happens along and finds it. She's in business.