mason bees

A mason bee covered in hairy-footed pollen mites

Above, a newly emerged mason bee wears a jacket of hairy-footed pollen mites. Hairy-footed pollen mites are common pests of mason bees. Technically, they are kleptoparasites, eating the food left for larval bees.

Inside: Hairy-footed pollen mites eat the food of larval bees and then hitch a ride on an adult bee to flowers with pollen or a new nest with pollen. The mite population expands until an infested bee can barely fly.

A nasty case of pollen mites

I try to remain vigilant for mason bee mites and I use recommended control measures to limit their population on the few mason bees I have. But earlier this year I saw my first terrible 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 wondered what was going on. After several hours of commotion, two masons emerged into the space between the window and the screen.

The masons nested in a drain hole

The adult female must have crawled into the tiny drain hole on the outside of the window frame last year. This spring, the newborn bees emerged through the other end of the hole. I thought the whole thing was adorable until I looked closer: each of the bees was covered with what looked like sticky brown fluff—an infestation of hairy-footed mites.

The infestation was so bad that I suspect mason bees have been nesting in those drain holes for a couple of years or more. 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 bee was rising on its hind feet trying to fly, but the weight of the mites was overwhelming.

The pollen mite is a kleptoparasite

We call the hairy-footed mite (Chaetodactylus krombeini) a pollen mite. A special nymph stage, called a hypopus, rides around on the back of an adult bee 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 left, 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 debris filling a cell—a sure sign they were busy eating and reproducing for a long while.

Surviving bees carry the mites to new nests

In the spring, surviving bees crawl through the nesting cavity where they pick up many of the phoretic nymphs. The nymphs instinctively grip the bee and do not let go. From there, the bees unwittingly carry them 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.

Rusty
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28 Comments

  • Poor thing!! Can you do anything for the poor bees that you find in this condition? Do these kind of mites affect honey bees too?

    • There’s nothing you can do once it happens. The mites have special feet that clamp into the bee very firmly, and most chemicals that kill mites also kill bees. It’s best to prevent the mites in the first place.

      And, no, honey bees do not get this type of mite and this type of bee doesn’t get honey bee mites. They are very specific.

      • Thanks so much Rusty! I LOVE your site and pictures. It’s been SO helpful since I just getting started with my bees.

      • Well here goes nothing, The mites that are after honey bees are sometimes repelled by using powered sugar. Might be worth it to try some on a few bees to begin with. Hope this helps.

        • Julian,

          Honey bees are not repelled by sugar, but they do try to groom it off their bodies. In so doing, they may remove a few mites, but most mites are securely anchored under the abdominal plates where they cannot be removed by the bees.

          Pollen mites grow inside the sealed brood cavities along with the bee pupae. You have no way to get powdered sugar in there and the pupae have no way to remove it.

  • I’ve a little bee house for mason bees in my garden here in England and ‘Ive noticed 2 mason bees that are flying around and frantically landing and trying to dislodge the mites on their backs and heads… they look just like the one in your picture… should I take apart the bee house and clean it??
    Feel so helpless for them… 🙁

    • Alexandra,

      Over here, it is recommended that you change the tubes every two to three years to avoid a build-up of parasites. Some people line the tubes with parchment paper. Then, at the end of summer, they pull out the parchment and put the cocoons in cold storage until spring. I think you can disinfect the tubes, although I’ve never seen a good description of how to do it.

  • Rusty,

    I guess now is a good time to ask this; could one put frames or bee blocks in a container and burn sulphur like is done to make sulphured apples? Seems it would sterilize well if it didn’t harm bees.

      • I have burned sulfur before and it is an extremly toxic chemical that my grand father used to use when he got sprayed by a skunk. He would place his clothes under a upside down bushel basket an a add a small amount of sulfur in a fire proof container and lite it. When it was done burning, his clothes didn’t smell any more .

  • I’m having this problem just now. My first year of mason bees have not long emerged and I have noticed some small yellow crawling things on the outside of one of the tubes. There was actually a dead bee half out the tube and within a day the full dead bee was covered in mites. I managed to knock most of these off with sand and I got rid of the dead bee. I’m at a loss at what else I can do.

    I don’t know much about mason bees but I have noticed that when the weather turns rainy, the female bee sits inside her tube. She has made a wall of mud and tucks herself in behind it while leaving a head sized hole to look out of. Do the female bees remain with her eggs and just end their life in the tube?

    • Jill,

      I don’t know what you can do at this point. Folks in the UK tell me the mites don’t do much harm to the bees and that the bees can live side-by-side with the mites.

      Most bees do not fly when it rains, but seek cover. The females will often stay with the nest until the weather clears. The female will not remain with the eggs, but will probably die while out foraging for pollen or nectar.

  • The tubes are filled and the mason bees have stopped activity. Now some of the tubes are becoming empty.

    Is it because of mites or some other insect? What can I do?

    • Pat,

      It could be parasitic wasps, birds, or any other predator. As soon as the tubes are filled, take them inside and store in a cool, dry, predator-free place until next spring.

  • How do you eliminate mites from the cocoons before you store them for the winter?

    I read somewhere if you mix 1/4 cup of Clorox bleach with a gallon of water, soak the cocoons for 2 to three minutes to kill off the mites without harming the bees in the cocoons. Is this true?

    • Yes. I use one tablespoon of bleach per cup of water, agitate for one minute, then drain, rinse, and dry the cocoons.

  • Can the mason bees remove the mites by themselves? I have lots that are absolutely covered in them and are attacking the ones that don’t have mites. But we also have ones that are fine and some with maybe a few mites. Can they remove them from each other or themselves??

    • Lexi,

      They can probably remove some of them. Pollen mites aren’t like varroa mites because they don’t bite the bee. They just use the bee to get a ride to a flower where they can jump off and get a ride on another bee and into its nest. Inside the nest, they eat the pollen. The problem with mites on adult bees is that sometimes the mites are so numerous and heavy that they make flight impossible. If you catch the bee, you can wipe most of them off with your finger.

      • Hey, had a few of these bees covered with mites. I did catch one of them, and I put him in the refrigerator so that he would go dormant. Once he was quiet, I went into the glass jar, and used the dull side of a needle to try to remove some of the mites but, they did not dislodge easily at all. I also took some bee pollen from my refrigerator, ground it in a mortar and pestle, and then put the pollen powder in the jar with the infected bee.

        I was sort of hoping that the mites would jump off of the bee and head for the pollen powder but, really, the pollen stuck to the bee and it just made the mites super active. They did not jump off at all. I think they were just pretty happy to have a bunch of pollen. Also, I was reading that once these things eat pollen, it triggers the next stage of the reproduction cycle. So, in the end, I decided it was really a terrible idea to put pollen powder on the bees to try to rid them of the mites.

        I did manage to scrape a pretty hefty pile of mites from the bee itself and then tried spraying the mites with isopropyl alcohol but, the isopropyl alcohol did absolutely nothing to these mites. They were swimming around in that alcohol like it was a piña colada. I did find a tube made from paper that was covered in these mites. It also had three chambers left. I opened one of the cocoons, and a female crawled out, and she already had the mites on her. So, somehow they penetrated the cocoon and were already on this female bee. One comforting note is that the bee was alive. So, I’m guessing the mites did not eat all of the pollen in the chamber but, I’m not completely convinced that these bees that are infected with these mites won’t eventually harm what does otherwise healthy colony.

        I’m also not completely comfortable with the idea that these bees that are infected with the mites are flying around and dropping these parasites onto other plants that are in affecting my native bumble bee population.

        I’ve decided that, rather than jeopardize, my healthy colony, I’m gonna capture the infected bees and destroy them. I really hate doing it but, I also really hate the idea that they could wipe out the rest of my colony, which is many times larger than the number of these emerging with this mite problem.

        • David,

          These mites are called “pollen mites” for a reason. They eat pollen as their primary food source for raising their young, just like the bees do. They are considered to be kleptoparasites because they invade the nest of another species and hijack the supplies for their own use.

          The mites likely didn’t penetrate the cocoon but transferred to the larvae while they both were eating pollen. Later, the cocoon was spun around both.

          Slowing the spread of these things is a good idea, but I agree it feels terrible to kill the bees.

  • Rusty, my poor bees are literally covered in the mites. They can’t even fly. I have cleaned out the my bee houses but I just don’t think I could face using them again just in case. I have tried wiping the mites off but they seem stuck on. The bees have just been landing on my hands and letting me try. I am heartbroken.

    • Maria,

      I agree it is heartbreaking to see. I’ve begun using new tubes and emergence boxes each year.

  • I have been experimenting for the last couple of years using diatomaceous earth on the cocoons to remove mites. After I remove the cocoons from the nest I put them on a screen and using a sort of salt shaker I made with tiny holes I dust the cocoons with a very light coating. I also roll the cocoons around on the screen. The diatomaceous earth adheres to the mites and helps loosen the mites from the cocoon. I put the powdered cocoons in a jar in the frig for a month or so then take them out and do a wash. After drying, more powder and back to the frig. Before putting them out in the spring I give a final rinse and dry. The way this stuff works is by getting between insect joints.

    I suggest looking up the use of diatomaceous earth for insect control. A big bag is cheap and I get it directly mailed from “Diatomaceous Earth.Com”. I eat it as a food supplement so it’s safe. Just be sure to remove it from the cocoons before you put them out in the spring. Doing this last year I didn’t have almost any bees that didn’t hatch, still had some mites but a lot fewer. Still working on a more efficient way to kill every one of those nasty little bastard mites. Any suggestions please send me an email. Also, send this idea to anyone that you feel may find it useful. I don’t find the bleach works very well.

    Jim Martin Email: maarrttiin@msn.com