I try to remain vigilant for mason bee mites and I use recommended control measures for limiting their impact on the few mason bees I have. But earlier this year I saw my first really bad case of hairy-footed mites on the backs of two newly-emerged mason bees.
The bees in question emerged not from my mason bee houses, but from a little moisture drain on the bottom of a bedroom window. I heard the window buzzing and I was perplexed as to what was going on. After several hours of commotion, two masons emerged into the space between the window and the screen.
The adult female must have crawled into the little drain hole on the outside of the house and, the following spring, the new-born bees emerged through the window frame. I thought the whole thing was adorable until I took a closer look: each of the bees was covered with what looked like sticky brown fluff—in other words, an infestation of hairy-footed mites.
The infestation was so bad that I suspect mason bees have been nesting in those drain holes for more than one season. I tried to photograph them through the glass (which didn’t work so well) but you can see the coating of mites, which looks something like a brown shearling vest. One of the bees was rising up on its hind feet trying to fly, but the weight of the mites was overwhelming.
The hairy-footed mite (Chaetodactylus) is also known as the pollen mite. A special nymph stage, called a hypopus, rides around on the back of an adult bees until it finds a source of pollen to eat. But frequently the adult bee unwittingly takes the mite home. The mites reproduce within the larval chamber where they eat the pollen provisions the bee left for her own offspring. With no food stores, the bee larvae die. Sometimes the mites eat the bee egg or larva as well. If you open a mite-infected tube, you can often find a mass of orange-colored mite debris filling a cell—a sure sign they were busy eating and reproducing for a long while.
In the spring, surviving bees crawl through the nesting cavity where they pick up a great many of the phoretic nymphs that are designed to grip onto the bee and not let go. From there, they are carried to flowers or into new nesting cavities.
The mites are native to North America and can infect many of the bees in the Megachilidae family, which includes the mason bees, leafcutters, and carder bees. They prefer damp environments—one reason they are proliferating in the coastal Pacific Northwest.
No Vacancy at the mason bee condo
It took them awhile, but the entire condo is filled–as well as the tubes they hatched from. A job well done. I will miss these little bees who are around for such a very short time.
Although I haven’t actually seen many mason bees around, it is easy to see they’ve been hard at work. This mason bee condo was empty two weeks ago. Now there’s only two spaces left and the lower one has a mason bee in it. The tubes on the left are where they hatched, and those are filling up again too. I have other condos, but this one is sheltered by an eave and they seem to like it the best.
I finally put out my tubes of mason bees about two weeks ago. Last year at this time, the mason bees were flying and the pear trees were in bloom. This year, it is still cold and rainy. The lawn splats when I walk across it and the paths to the outbuildings are slippery and slidey.
One intrepid mason bee has been sitting in his tube looking out for nearly a week. I know he’s alive because he changes position now and again, but he doesn’t dare leave the comfort of his tube. A few other mason bees are breaking through the mud barriers but none have taken flight. It seems like we are making up for last year’s early spring.