This has been a season of firsts. I love to try new things and this year I’ve experimented with new styles of pollinator housing, three new types of comb honey supers, new honey bee feeders, new watering methods, and many new bee plants. Of all the bee plants on my list, I was most excited about Autumn Joy sedum.
Last winter as I collected the data for the Plant Lists, I was continually amazed at how many folks listed Autumn Joy as one of their top bee attractors. I had never even heard of it but quickly went out and purchased six plants and then further divided them until I had a bunch. All summer I had to protect them from my husband’s projects, which included flying pieces of wood, ballooning stretches of tarp, air-borne shingles, tipped ladders, and dropped tools. Somehow, the plants (and my husband) survived the summer and now as fall approaches, a few of the Autumn Joys are beginning to bloom.
The first bee arrived with the first blossoms (Yay, it’s working!). Unlike the sunflowers, the Autumn Joy are down near the ground where I can actually photograph them. Also unlike sunflowers, they come without a dark center—there’s nothing like a brown bee on a brown background for an impossible portrait.
My first Autumn Joy visitor was a small carpenter bee, Ceratina. These little sprites give me anxiety disorder—they are super small and fast and seem to quiver in the air, vibrating as they approach a flower. They look like they need to inhale deeply. In fact, they make me so nervous I find myself holding my breath as I watch them. I suppose all the extraneous movement protects them from being eaten, but it sure makes them hard to photograph. Luckily, the Autumn Joy held this one’s interest long enough for me to get a shot.
Most of us who want to attract native bees to our yards and gardens do so by providing housing in the form of tubes, straws, hollow reeds, or drilled wood. While there is nothing wrong with this, the irony is that fully 70%—or nearly three-quarters—of all bee species live underground. Above ground cavities are completely useless to most bees.
So, if we really want to attract a variety of bees, we need to prepare space for the ground-dwellers. This is not an easy task, which is why it is frequently overlooked.
Many people don’t have land available for bee habitat. Some folks live in apartments, condos, or subdivisions where it is easy to have a few drinking straws on the porch but impossible to have a patch of bare earth. Others live in areas where bare earth is considered an eyesore. Still others live where the soil is mostly covered in asphalt and concrete. Nevertheless, there are things we can do.
What the bees need
Ground-dwelling bees like sandy soil, such as sandy loam, that is damp but not wet. It should be bare—free of plants and their annoying roots. It should be gently sloped, about 30 degrees is nice, and should face south or southeast in a sunny location. In addition, it should not be covered with mulch of any type. But here is the kicker—something that’s easy to forget: it must remain undisturbed nearly all year.
Why undisturbed? Because unlike honey bees, most native bees hibernate underground for about ten months of the year. They spend this time as a pupa or an adult, depending on the individual species. If we disturb their nests by tilling, disking, or shoveling the soil, we kill the bees.
How to do it
Researchers have found that even small bare patches can be useful for bees. While some native bees nest in large aggregations containing thousands of nesting holes, others build off by themselves wherever they find a good spot.
You can build “scrapes,” which are simply patches of earth with the plant life scraped free. You can build forms out of wood or brick, and fill them with sandy loam sloped toward the sun. Or you can truck in soil and just mound it in a sunny location.
Even a flower pot can be used. So if you live in condo with a balcony, for example, you could have several pots with flowers and one with bare soil that you water occasionally. Dampness is necessary for the bee tunnels to maintain their shape; if the soil gets too dry, the tunnels may collapse.
The sandy loam should be about 50 to 70% sand. Since you are not growing plants in it, the percentages of clay, silt, and organic matter are not too important. To make loam for bees, in most cases you can just take your native soil and mix it with an equal amount of sand.
When will they come?
In a study in Oxfordshire UK, where they dug four 3 x 5 m nesting plots, solitary bees nested in the first year. During the next three years, 80 different species of solitary bees and wasps colonized the plots . Other similar experiments in Europe and Oregon have produced nests during the first one to three years.
Give it a try
If you decide to build an underground bee bed, take some photos and let us know what you did. This is new territory for most of us, so any hints, suggestions, or bee stories would be especially welcome.
 Gregory S. & Wright I. (2005) “Creation of patches of bare ground to enhance the habitat of ground-nesting bees and wasps at Shotover Hill, Oxfordshire, England.” Conservation Evidence, 2, 139-141.
The problem with bumble bee boxes is getting the bees to move in. Depending on the type of house and the location, average occupancy rates range from about 10% to 60%, but the number I see most often is 30%. So how can you in increase it?
One thing obvious about bumble bees is that they like birdhouses. Birdhouses frequently become bumble bee houses, but only after the birds have done all the work of collecting materials and building a nest. Bumble bees also like used rodent burrows for the same reason—they are completely furnished and move-in ready.
Commercial birdhouses often come with upholsterer’s cotton to attract bumble bees, but the bees prefer used nests every time. It could be they like grass and feathers better than cotton, or it could be that used nests have an odor the bees can detect which helps them find the nests in the first place.
Several people have recommended collecting rodent nests to line the bee boxes, but not being a real rodent fan, I’ve begun collecting abandoned bird nests for my bumble bee dwellings. The bird nests I have so far are from small birds that use small bits: moss, feathers, dog hair, threads, and grass. It seems to me that bees, being small themselves, would like smaller nest materials, so I decided to collect that type.
The literature on bumble bees is somewhat confusing. Many people have studied ways to attract bumble bees, but most papers show vastly different results. Most agree that buried boxes are better than ground level boxes which are better than just-above-ground boxes. Almost no one mentions birdhouses, but one of the most common queries I get is “How can I get rid of the bumble bees in my birdhouse?” The collection of bird-turned-bumble-bee houses at Oregon State University further confirms this common phenomenon.
Another thing people are doing is catching bumble bee queens in the spring, placing each one in bee box with a little honey and some nesting material, and locking them up for a couple days—sort of like saying, “This is your house now! Get used to it!” I’m not convinced this is a good idea—it seems intrusive—but it is similar to what we do with a package of honey bees. Maybe it’s worth a try? I’m still thinking on it.
Anyway, I mention this now because if you want to try using bird nests next spring, now is a good time to collect them—they are empty and haven’t yet been ruined by winter storms. I can’t guarantee results because I’m still in the “try it” stage, but it seems like an experiment worth pursuing.
The conventional wisdom about nesting blocks is that you take a 5/16-inch bit and drill holes that are roughly 5-10 inches long. This will attract orchard mason bees, which is typically what people are trying to do with nesting blocks. But recently my whole attitude toward these blocks was changed by Michael Burgett, Emeritus Professor of Entomology at Oregon State University.
He showed me the nesting blocks at the Oak Creek Center for Urban Horticulture and I was amazed. Not only were the holes all different sizes, but they were tiny . . . and they were full of bees. The trick, he said, was to start with a 1/4-inch bit and work down from there and not to worry about the holes being too small. Not only that, he said the tiniest holes would fill first.
Intrigued, I went back to my room that night and ordered a series of bits to be sent to my home. I decided on 1/16, 3/32, 1/8, 11/64, 7/32, and 1/4-inch diameters. (This doesn’t seem so cryptic if you think of it as 4/64, 6/64, 8/64, 11/64, 14/64, and 16/64.) All of them are 6 inches long except the 1/4-inch, which is 12 inches long. The narrower holes don’t have to be so deep, so you can use shorter bits for those.
When the bits came I made a small experimental nesting block. I drilled about 7 inches deep with the 1/4-inch bit and 4 to 5 inches with the others. Then I added a little rain roof and hung it up. I honestly didn’t think it was going to work—after all, it was already past mason bee season and I hadn’t seen many other bees around.
Nothing happened for a week, but then one day I noticed one of the smallest holes was sealed up with a glittery resin-like substance with wood splinters mixed in. I was elated.
Now that it’s summer, many of the holes are full, and there’s no doubt that the smaller ones went first. I’ve watched the tiniest little bees disappear into holes I can barely see. More bees sealed their nests with resin, then others began using mud. Some of the seals look like chewed leaves and some like sand. It is awesome. Right now I’m getting what I call summer mason bees, a species of Osmia that is active in summer instead of spring. The summer Osmia are using the 1/4-inch holes, even though the spring Osmia used 5/16-inch holes in my other nesting blocks.
As a result of all the tiny holes, I’ve seen species I never even noticed before. It’s been both fun and educational, and I run out there every morning to see what’s hanging around. In fact, it is so much fun I fully intend to spend the cold nights of winter designing nest blocks and drilling holes.
If you’ve made or purchased a bumble bee box, you are probably wondering where to put it and how to attract tenants. I’ve scanned dozens of documents looking for the secret formula and learned that location is the most important criterion, followed by nesting material. Moisture control runs a close third. Even so, most bumble bee enthusiasts report an average occupancy rate of about 30 percent.
What follows is a summary of all the suggestions I found. I have a bumble house that I purchased several years ago that I use for show-and-tell, but I’ve never actually set it outside. After one more demonstration later this week, I’m finally going to try it. We get lots of bumbles here of various species, so I’m cautiously optimistic.
I’ll start with location since it is important and comprises many variables:
According to The Natural History of Bumblebees by Kearns and Thomson, “by far the best site is a south-facing bank.”
The box should be placed in full or partial shade. If the interior gets too hot, the larvae will cook. If the box will be in the sun part of the day, morning sun is better than afternoon sun.
The box opening should face the morning sun (east or southeast) even if it is not directly in the sun.
The box should be sheltered from the wind.
The entrance should be at ground level.
Other good nesting areas include:
Under a hedge
At the base of a fence
Alongside a garden shed or wood shed
Bumble bees do not collect nesting materials so they select nest sites that are already outfitted with the materials they need. In nature, they often select rodent burrows, birdhouses, leaf litter, or debris piles. You have a much better chance of attracting bumble bees if they approve of your choice. Possible nesting materials include:
Upholstery cotton or cotton batting (surgical cotton is too fine and may entangle their legs or wings)
By the way, if you have a two-chambered box, the nesting material goes in the inner one.
A bumble bee may set up a nest only to move out if the nest becomes damp or water-logged. To control moisture, place the nest box on a concrete block and provide an over-hanging roof. You can also drill several small drainage holes in the floor of the box. Be sure the nest location is away from sprinklers.
Due to moisture problems, some people prefer to mount the boxes 8-12 inches off the ground, attached to a fence post or building. This above-ground entrance will work for some–but not all–species of bumble bee.
The nest should be placed within a half-mile of early blooming plants, but the closer the better. If you put the box in an area where bumbles are common, you have a better chance of attracting a nesting female.
Secure the box to avoid predation from small mammals such as opossums, raccoons, mice, weasels, voles, moles, and shrews that enjoy a savory meal of bee brood. Ants can also be a problem around bumble bee nests. Bumble bees like a secluded spot, so choose an area away from pets and human traffic.
In many parts of North America the early queens will start house-hunting by mid-February, as soon as the earliest flowers begin to bloom, so it’s not too soon to set out your box.