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.