Why Do Some Bees Just Seem to Be Camping Out in the Blocks, but Not Building a Nest?

Sometimes you may notice bees and wasps staying in your bee blocks, but not actually building a nest. Here are a few photos of this behaviour sent to us from our customers (explanation below):

The first three photos above are of male ground-nesting bees - that is, the females will nest in the ground instead of in cavities in wood - while the last photo is of a crabronid wasp. So why do we sometimes find them in our bee blocks?

Male bees of various species will often hang out in empty blocks, particularly at night or when it's cold or rainy out. This is because they don't have a home nest to go back to: once they leave the nest where they were born, they're essentially homeless, since they don't participate in nest construction like female bees do. The blocks provide a safe, temporary shelter for them - i.e., these bees are in fact just camping out.

I honestly don't know why these crabronid wasps hang out in the blocks. We see them regularly at our field sites, but this particular genus never builds nests in the blocks. They, too, might just be using the blocks as temporary shelter, or maybe they are considering using them as nests but find them to be unsuitable in some way. If somebody out there knows, let us know!

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Dr. Jessica Forrest
Associate Professor of Biology, University of Ottawa
Head of the Forrest Lab

Have bee footage or videos you want us to explain? Send them to creatures@scopabio.com!