Digging Digger Bees

digger bee up close

A couple months ago I noticed a cluster of soil mounds in my driveway. They looked like anthills, but I didn’t see any ants. What I did see: lots of bees flying about.

These are “digger bees” – ground-nesting bees that excavate a series of vertical and horizontal tunnels in the earth. It turns out that 60 percent of the bees in my state of NY are ground-nesting, solitary bees. They might live alone, but they often build their nests in bee villages, or aggregations. Sometimes those villages can be dense, with more than 100 nests in a square yard. Mine aren’t nearly so crowded; there are only 4 to 7 nest sites in a square foot. Perhaps that has something to do with my clay-filled soil and stony hard-packed drive.

They don’t always dig in driveways; some build their nests in lawns or on the banks of streams. Check out your neighborhood. If you are lucky enough to have digger bees living nearby, spend some time watching them. They don't seem to mind being watched. Here's a few questions you might want to ask:

• Where do they build their nests? What is the soil like: is it dry or wet? It is sandy or hard clay? Are there lots of rocks in the soil or is it in the forest beneath leaves and duff?
• Do different kinds of digger bees choose different locations for their nests? Does the same bee build nests in different kinds of soils or environments?
•  What is the nest density: how many nests in a square foot, or square yard? To find out, measure a square and count the number of soil mounds you see. You might want to make a map of your nests: are they spaced equally apart or are they clumped? If you have a smaller ruler you could measure the distance between nest entrances.
• Watch your bees over time. When do they get up in the morning? Are there times when they are more active? What happens if the weather gets really cold or really hot? What happens if there’s a big rainstorm?
• When the bees return from collecting pollen, what do they do? Do they circle over the area first?
•  How can a digger bee tell which is her nest when all the dirt mounds look alike? Do your bees use landmarks – and how could you test whether they do?

Check out the other STEM Friday posts today... and squeeze in a little time to check out the bees in your neighborhood.