Yellow bands of hair across top of abdomen and two small horns at the base of the clypeus (see 2nd photo). Foraging at Rudbeckia in a suburban garden. Scopa under the abdomen identifiers her as a female.

This observation inspired me to write the following article.

The Faithful Leafcutter Bee
During August and September you may have seen the female faithful leafcutter bee, Megachile fidelis, in your garden. She would have been foraging on flowers of the aster plant family such as Rudbeckia, sneezeweed (Helenium) and blanket flower (Gallardia). In Canada, she is found in mainly two locations: the southern Okanagan Valley or here on the east coast of Vancouver Island as far north as Campbell River.

She belongs to a family of bees called leafcutters or Megachilidae. Like other bees of the leafcutter family, her scopa or pollen carrying hairs are located on the underside of her abdomen. However, unlike all other Megachilidae in our local area, she is unique in having broad, even bands of yellow hairs running across the top of her abdomen.

Like the blue orchard mason bees, she nests in hollow plant stems, empty beetle tunnels found in wood and bee boxes. But she is picky, and will only nest in the tunnels if they have a diameter of about 5 mm.

For her brood, she builds cells of finely chewed up plant leaves mixed with mud. Each cell is provided with a pollen ball and only one egg is laid before another cell is constructed. To keep insect predators and parasites from attacking her brood, she plugs the tunnel entrance with roughly cut and sometimes resinous leaves.

The faithful leafcutter bee has another common name: the horned-face leafcutter bee. This name is given to her because she has two small projections or “horns” found on the lower part of her face (arrow in photo above). The horns are very difficult to see with the naked eye and are best seen if you can get a good close-up picture of her face.

Science Fact or Science Fiction?
In the past, I recall reading that the adult female bee uses her body to block the entrance of the tunnel to protect her brood. This is why she was given the specific name “fidelis”, which means faithful in Latin. However, I cannot find any scientific references to this behavior. So, until I have a chance to observe the faithful leafcutter bee in action at her nest, this behaviour, in my mind, remains questionable. And maybe you too, inquisitive reader, might like the challenge of finding an answer to this question?

References
Sheffield, C. S., Ratti, C., Packer, L., & Griswold, T. (2011). Leafcutter and mason bees of the genus Megachile Latreille (Hymenoptera: Megachilidae) in Canada and Alaska. Canadian Journal of Arthropod Identification, 18, 1-107.
Steele, S. K. (2021). Nesting Habits of Cavity Nesting Bees and Wasps in Portland, Oregon (Doctoral dissertation, Portland State University).