About a year and a half ago, I posted some information about solitary Mason Bees... how they're important native pollinators, and how you can help sustain their numbers by providing a good spot for them to shelter and lay their eggs. This past spring, I decided to give it a go myself.
I purchased a basic house from Ruhl Bee Supply, then I added a larger roof using some metal flashing, to better protect the bees and the paper tubes from spring rains.
I put it on a post against a south-facing wall, with the opening facing east so the housing material would be warmed by the morning sun.
Then I drew a Mason Bee on the side...
...and filled it up!
I used cardboard tubes with paper inserts (also purchased at Ruhl Bee Supply), and I added some spacer blocks and twigs left over from pruning my Red-osier Dogwoods. Apparently it can help the bees identify which tube they're filling with eggs if you break up the space and make it a little random and natural-looking. (Those Red Osier Dogwood twigs turned out to be a lucky choice, but more on that later...)
I decided I didn't want to rely on the curb appeal of my new bee house to attract the bees, so I bought a small box of Mason Bee cocoons from Portland Nursery (supplied by Crown Bees). Here's a picture of my supplies. Each cardboard tube has one closed end and one open end. The paper tubes are open on both ends, and slide into the cardboard tubes to make one ready-for-eggs tube.
When the weather seemed consistently warm enough, and some of the native early blooms were opening in my yard, I took the box of cocoons out of the refrigerator where they had been waiting patiently, poked a hole large enough for the bees to emerge, and placed it in the top of the house.
A few days later, I was lucky enough to catch one of the bees as it left the box and explored the new digs. I think it might be a male because it was kind of just hanging around. The males emerge first (my box of 10 cocoons had 4 male and 6 female cocoons), then wait for the females to emerge so they can do their thing. Then the females can get on with their business of gathering pollen and nectar, placing it in a tube with a single egg, then adding a wall of mud to create a chamber. They'll repeat this process until a tube is full, and move on to the next one for as long as they're able.
I enjoyed watching my Mason Bees fly back and forth, industriously going about their work. Because these solitary bees are so docile, you can stand right in front of the house and they will just fly around you on their way in and out. I think I ended up with three or four females working in the house. All of my cocoons hatched, but I think a couple females flew off or maybe had an unfortunate run in with a hungry bird. You can put large mesh or wire in front of the house to protect the bees from any lurking birds as they come and go.
I provided a tray of mud at the base of the pole, to make sure the bees had a source, but I don't think they ever used it. I guess during spring in Oregon, it might not be too hard to find a good spot to pick up some mud.
I didn't make a note of when I saw my last live bee working, but I believe by mid-July they were all done. One of them died in the end of a tube while trying to pack in that last egg chamber. You can see it's iridescent bee-hind in the photo below (top, left of center).
Some people recommend taking the nest tubes out of the house after the bees stop flying, and placing them in a protected space with natural temperatures. The idea is to protect the eggs and larvae from parasitic wasps (which can drill through the nest tubes to lay eggs of their own) as well as other pests and predators. I decided that my house was well-packed enough that no wasps could get in, so I thought I would just let them stay in the house until the time comes to remove the cocoons and check for mites this fall. (If mites are present you can rinse the cocoons before storing them through the winter.) So that's what I did.
It turned out to be a fortunate choice.
After returning from a camping trip the first week of August, I was walking past my bee house and just happened to notice a very small bee crawling around the twigs. My first thought was "Oh no! It's a tiny parasitic wasp with bad intent! All my larvae are doomed!"
I took a closer look, and realized the tiny bee - probably 1/4 the size of a Mason Bee - was excavating the soft centers of the Red-osier Dogwood twigs, presumably to lay eggs like the Mason Bees had done in the cardboard tubes.
This bee may look large in the photo above, but the end of that twig is only about 1 centimeter in diameter. And a few of the twigs that the bee was able to excavate and crawl into were as small as half a centimeter in diameter! While I was standing there, happily watching this second species of bee making use of the house I provided, a second tiny bee flew in to join the first. They would crawl into one of the twigs, and push out little bits of "sawdust" as they dug deeper into the twig's core. Then I noticed that some of the excavated twigs had already been capped off. But it didn't look like the capping material was mud because it had a definite green tint.
In the photo above, you can see the green-capped twig, as well as a partially excavated twig and several that remain unexcavated.
I had no idea what this new micro-bee was, so what would any curious natureophile do? TO THE INTERNET!!
From the information I was able to find, I believe my new tenants are Leafcutter Bees (Megachile spp.). Leafcutter Bees nest in holes or excavate pithy plants (like pruned rose canes), and they use either chewed-up bits of leaves or neatly trimmed pieces to make their egg cells. Leafcutter Bees (and Mason Bees) don't collect the pollen on their legs like Honey Bees. They collect it on the underside of their abdomen. You can just make that out in the photo below if you click to zoom in.
My Leafcutters were only around for two or three weeks. From late July to mid-August. But I have quite a few capped-off twigs, so hopefully - between my Mason Bee tubes and the Red-osier Dogwood twigs, I'll have a big batch of bouncing baby bees come next year. My plan is to remove and clean the Mason Bee cocoons this fall, remove the twigs, and store them all either in my unheated shed, or maybe in the refrigerator. (I fear my wife may influence that decision in one definite direction.) I'll be sure to keep you posted.
So start paying attention to little holes around your yard - you may be hosting some native pollinators without even knowing it. That's what happened to Mike over at Native Plants & Wildlife Gardens. And even though I purchased my Mason Bees, the Leafcutters found the twigs on their own. So I guess if there's a moral in this blog post, it has to be... "If you build it, they will come."
For more information on Mason Bees, and a link to some great resources, read my earlier post on Mason Bees. Or check out a book called Attracting Native Pollinators: The Xerces Society Guide for information about a multitude of native pollinators.