After they mate in the spring, the female lays an egg inside a deep hole, adds some pollen (food for the larvae), and then seals it up with a bit of mud. The female repeats that, laying eggs, adding pollen and sealing with mud to create many chambers per hole. The larvae hatch in the summer, spin cocoons, and then hibernate all winter. They emerge next spring as adult bees and the cycle repeats.
You can buy pre-made mason bee houses at your local hardware or garden store, but making a Mason Bee house is easy. Here's a design I came up with that uses hardware cloth (like "chicken wire") for the main body. That allows easy access for the bees to go in and out but keeps out foraging critters, like birds and squirrels. The slanted wood top has enough overhang to keep them dry but with plenty of ventilation. The wood back holds it all together and provides an easy method to hang the house on a fence, tree or post. I used unfinished cedar for natural resistance to weather. When finished, hang your bee house on a fence or mount it on a sturdy cedar stake.
You can buy special paper tubes or slotted wood trays for nesting materials for the bees. (Blocks of solid wood with a pattern of drilled holes aren't recommended, as they can harbor pollen mites.)
½" Hardware cloth, bigger than 21" x 16"
1" x 8" cedar board (which is closer to ¾" x 7 ¾"), about 2 feet long
8" of 5/16" diameter hardwood dowel
4 brass screws and trim washers
A few inches of rustproof wire (brass or stainless steel or use gardener's wire)
Pliers or vice grip
Disc sander or grinder
(I based this design around the size of the slotted bees nest we bought. Adapt the dimensions to suit.)
Lay out the shape of the unfolded house on the wire with a black marker. Use the 1/2" squares for measuring.
Draw the diagonal folding line with a straight edge. Cut out the shape with snips. Make all cuts on the "spaces" between the connecting wires, just outside the marked lines. Be sure to wear gloves--the snipped wires are sharp!
I used a disk sander to grind down the sharp points on all the cut wire. You could alternately bend them back with small pliers.
Bend the wire cloth to make the basic shape. I used a long work vise to help make the bends. You could clamp the edge of the wire cloth between two boards for the same effect. Bend one row of the grid 90 degrees. This makes the flange for mounting to the wood back.
Fold the angled edge over. Use pliers to squeeze the bend flat.
Use a scrap of wood as a handy straight edge guide for making the other bends.
Cut the back and roof pieces out of the piece of cedar. Measure and draw a line 11" from the end to divide the wood in half. Then cut along the line at an angle of 65 degrees. That gives an angled back edge on the roof panel and a matching angled top edge on the back panel.
Attach the wire body to the back panel using the brass screws and washers as shown. Twist some rustproof wire to hold the open corners together.
Place the roof in position so that it overlaps the back and has an overhang on the front.
Then turn the whole thing upside down. Make marks on the underside of the roof just inside the wire body. This is where the dowels will go to hold the roof in place. Mark each inside corner and one mark on each side halfway between the front and back.
Drill 5/16 " holes at each mark. Drill the corner dowel holes angled to match the slope of the roof. The side dowels can be at 90 degrees.
Cut six 2" lengths of the wood dowel and tap into the holes.
Finally drill a nail hole in the back for hanging the bee house. Done!
Put your bee house in a sunny west or south-facing location, add your nesting materials and replace the top. You can buy mason bee cocoons at your local garden or hardware store. Keep them in the refrigerator, then place them in the bee house on a warm spring morning. You can time them to hatch with the blooms you want pollinated! I put the cocoons on top of a card inside the house so they wouldn't fall out where birds could get them --and it's fun to watch them hatch!
All our mason bees have emerged from their cocoons. We'll see how many will return to nest. Wish us luck!