Is a solitary bee a mason bee?

Confusion surrounding solitary bees seems to be getting worse. Recently, I ran into an acquaintance in a local supermarket. The conversation went something like this:

“Hey Kathy,” I said, “did you finally get your hive set up?”

“No, we decided to wait another year. But we got solitary bees! We put up a box.”

“Great!” I said. “What kind of bees are you seeing?”

She looked confused, “You know, solitary bees. Bees that live in tubes.”

Okay, I let it go at that point. I knew she probably meant the mason bee, Osmia lignaria, but I don’t think she did. And I don’t blame her; the confusion comes from Internet sites that equate mason bees with solitary bees.

Sure a mason bee is a solitary bee, but the vast majority of solitary bees are not mason bees. The two words are not synonyms. In fact, both terms are only descriptive categories that do not follow taxonomic classifications.

“Solitary” describes bee species where a lone female builds and provisions her own nest. “Mason” refers to species that collect building materials from the environment rather than secreting them. According to O’Toole and Raw (2004), “Materials include mud, resin, dung, and leaf and petal pulp. Some species also incorporate unchewed pieces of petals, wood chips, twigs and small pebbles in their construction.” Of the 20,000 species of bees in the world, the overwhelming majority is solitary, but only a portion of the solitary bees are mason bees.

Most mason bees are in the genera Osmia, Hoplitis, Prochelostoma, Chelostoma, Heriades, Anthocopa, Dianthidium, and Chalicodoma in the family Megachilidae. The other six bee families contain few, if any, bees that behave like masons.

Furthermore, not all mason bees live in tubes. Yes, all tubes are cavities, but not all cavities are tubes. Again, according to O’Toole and Raw, nesting spots for mason bees “range from irregular cavities under bark and rock, empty snail shells, hollowed-out gourds, and insect borings . . . others make nests on exposed surfaces such as rocks and walls; a few species dig their nests in the ground.” Did you catch that? In the ground.

The take-home message is this: the word “solitary” refers to bee species where a single female does all the work, including nest building, foraging, egg laying . . . you name it. The word “mason” refers to bees that construct their homes with collected materials. To refer to “mason bees” is like referring to “tree fruit”—it is a category that includes many different items. Neither “solitary” nor “mason” refers to any particular species.


This red Osmia nest is not in a tube; the partitions are made of mud. Photo © Stratford Beekeepers.

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