mason bees

Six myths about mason bees

Wherever you find beekeepers you are likely to discover plenty of misinformation, fodder for the old joke about ten beekeepers having a dozen answers. It doesn’t even matter what kind of bees they keep, which means mason bees are no exception.

Don’t get me wrong—I adore mason bees and I have kept them for ten years, problem free. They are fun to watch, easy to raise, and they are excellent spring pollinators. Nevertheless, they alone cannot save the world, in spite of what anyone tells you.

Which bees are masons?

Before I get to the myths, let’s clarify what bees we’re talking about. In its broadest sense, the phrase “mason bee” can refer to any bee that collects materials from the environment and uses those materials to build a nest for rearing its young. However, when melittologists (the people who study bees) use the term mason bee, they are usually referring to several genera in the family Megachilidae.

The Megachilidae family is a large group that includes leafcutting bees, resin bees, woolcarder bees, and of course mason bees. The family includes bees that collect all kinds of stuff, such as leaves, petals, pebbles, mud, fibers, plant resin, or sometimes things like builders’ caulk. Depending on the species, they can be pretty open to new ideas. These bees often have large jaws that they use to collect their treasures. In fact, Megachilidae means large jaw or large lip.

Myth one: all mason bees are native

When bee scientists refer to mason bees they are usually referring to bees in the genus Osmia, which in North American includes about 130 different species. When non-scientists talk about mason bees they are usually referring to Osmia lignaria, the blue orchard bee. But on the east coast, folks may be referring to Osmia taurus or Osmia cornifrons, both introduced species.

So there’s your first myth. Not all mason bees in North America are “native.” Osmia lignaria is native, and so are many others, but those other two popular species (also known as the taurus mason bee and the hornfaced bee) are most definitely not. Like the European honey bee, they were brought here for a specific purpose and have since spread across the landscape.

Myth two: mason bees don’t sting

The second myth has to do with stings. I hear it all the time, “Mason bees don’t sting.” That’s an interesting theory, probably started by someone who never got nailed by one. Mark my words, mason bee females have stingers and they know how to use them.

On the other hand, each time I’ve been stung by a mason bee it was my own fault. The first time it happened, one walked up my arm and got under my watch band. I didn’t know it, of course, and when I moved my arm, the band tightened and she let me know. The sensation was so light I wasn’t sure if it was a sting or not. I wasn’t sure until the spot raised up and turned red like a mosquito bite. It lasted about 15 minutes and then disappeared.

My other mason bee stings were similar and barely detectable, but I think it’s important to understand that they do sting. People who choose to get mason bees because they are allergic to honey bee stings should be wary. Would they react in the same way? I have no idea, but I would not assume mason bees are safe for a highly allergic person. Check with your doctor first.

Myth three: masons can replace honey bees

No chance. While mason bees are highly effective pollinators, the ones we normally raise are short-lived spring bees. They work great in orchards, but they disappear for the year before most crops begin to bloom. Although they make an excellent addition to honey bees, they will never be able to replace them.

The same problem applies to most bee species. Because honey bees live in a colony where the workers are constantly replaced, the colony stays active all year long. This means honey bees can pollinate whenever they have flowers and weather warm enough to fly. On the other hand, most native species are active only six to eight weeks per year, so flowers are dependent on many different bee species to do the work.

Myth four: you need to buy mason bees

If you are not a commercial operator, you do not need to buy mason bees. In fact, last year in a bumble bee identification class, a member of the Xerces Society was asked, “Where is the best place to buy mason bees?” The speaker was adamant and forceful in his reply, “Do not buy bees!”

The audience member persisted and asked more specifically, “What if I buy them from — (she mentioned a well-known supplier)?” His answer: “Do not buy bees!”

Then she asked about leafcutters, and he replied, “Do not buy bees!”

Why? Because most native bees live their lives in a very small area, one they are adapted to. Once you begin shipping them around, you also ship whatever diseases and parasites they might have. In addition, you are putting them into an environment they are not accustomed to and they may die.

When you look at honey bees and bumble bees, you can see the damage done by shipping. We have assured that honey bees all over the continent have shared their diseases and parasites. We have shipped infected bumbles bee around to the point where an entire group of species is in rapid decline and faces possible extinction.

Why do we want to repeat this folly with mason bees? Why can’t we learn from our mistakes? I have to side with the Xerces Society on this one. Distribution of native bees should be strongly discouraged along with sell-back programs. If they are not native to your own backyard, they are not really native.

If you want to raise mason bees, put up mason bee housing and be patient. You will get a few the first year, more the second year, and after a while you will have many. They will be locally adapted, strong, and free from imported ailments.

Myth five: you must clean and bleach cocoons

Cleaning and bleaching of mason bee cocoons is not something that happens in nature. It becomes necessary when you have large single-species populations living in close quarters. Many of the common diseases and parasites have always been there at background levels, but their numbers become amplified when the host population becomes congested. If you have thousands of mason bees, you must control diseases and parasites.

Several years ago, I wrote to native bee specialists at UC Davis and the American Museum of Natural History asking about cleaning and bleaching. Their answers were the same: if you are not running a big operation, cleaning and bleaching is not necessary. For the backyard mason bee keeper with a garden and a couple of pollinator condos, no interference is necessary. If you are not running a factory farm, levels of pollen mites and parasitic wasps normally will not exceed background levels.

Myth six: masons will save the planet

No one bee species will save the planet. Not masons, leafcutters, nor honey bees. Saving the planet is up to us, not the bees. The standard advice holds true for all species of bees: reduce the use of pesticides, plant a wide variety of flowers and flowering trees, leave undisturbed patches of ground for soil-nesting bees, and provide habitat strips and water. To those I will add another: leave the bees where they are. Let them come to you. We can’t buy and sell nature because buying, selling, and redistributing is not natural at all.

Honey Bee Suite

Myths about mason bees: Whoops. Yesterday I went to check on my mason bees that are stored in the garden shed and covered in fine netting to keep out predators. Four emerged while I watched. I'll call that "just in time" mason bee keeping.

Whoops. Yesterday I went to check on my mason bees that are stored in the garden shed and covered in fine netting to keep out predators. Four emerged while I watched. I’ll call that “just in time” mason bee keeping. © Rusty Burlew.

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  • You said, “ I would not assume mason bees are safe for a highly allergic person. Check with your doctor first.” Ha!

    Rusty, you may know as much about hypothetical mason bee allergy as my allergist, which would be close to zero. When tested for bee sting allergy, I was given a grid on my arm and challenged with a variety of Hymenoptera venoms (to which I only reacted to the honey bee) and I’m pretty sure no Osmia were mentioned. Honey bees, yellowjackets, some other nasty vespids, maybe a generalized wasp, and I vaguely recall some kind of ants, but no mason bees. Which doesn’t mean some poor unlucky person couldn’t be allergic, but it means that the doctor will be just guessing based on how other allergies work.

    Also, I know what you’re really saying, which is, “Don’t get your medical advice from the internet.” But your favorite answer of “It depends” works for medical questions as well as for beekeeping questions.

    Also, I appreciate the “Do Not Buy Bees” story, and I’m gonna try to do better on that. Maybe start with buying local bees next time. Although I would be ecstatically happy to have overwinter success ever after, and buy no bees at all.

    • Roberta,

      You’re right, of course. I don’t want anyone coming back (if they’re still alive) and saying that I said it was safe. No way. So I guess “it depends” on whether they are still alive enough to accuse me.

  • I’ve been told to never feed honey bees beet sugar, only pure cane sugar. I thought both are sucrose which is ok to feed bees. I’m I correct or do I need to stop feeding my bees beet sugar. Thanks

    • Jim,

      Sugar is sugar, and refined sugar contains nearly nothing else. If I need to feed, I use the cheapest sugar I can find, which is beet sugar. The “never feed beet sugar” crowd is reacting to the fact that most beet sugar comes from genetically modified crops. Cane sugar is most likely not genetically modified, at least for now. I hear that is going to change. In any case, the research papers that I’ve been able to read find absolutely no difference between the two, and no negative affects on bees.

  • Thank you for this springtime refresher on native bees…and the strong reminder to not/not purchase mason bees.

  • Thanks for the post Rusty! I monitored emergence from commercially supplied Osmia lignaria cocoons (advertised to backyard mason bee enthusiasts) and found ~5% did not contain Osmia: these were Monodontomerus (parasitic wasp) and Stelis (cuckoo bee). There are no regulations and quality control is at the supplier’s discretion. Starting out your mason bee project with non-local genetics and introducing some enemies of bees is a step in the wrong direction. Also, research indicates that failure of purchased mason bees can result because of the genetic bottleneck that happens when purchasing so few individuals, as a backyard ‘keeper’ would do. Myth busting on buying leafcutter bees (native vs. introduced) is also required.

    • Brian,

      Wow, that’s very interesting. A couple of cocoons filled with Monodontomerus could finish off your bees in a hurry. That’s one reason I don’t like the buy-back programs where a person raises cocoons and sells them back to the supplier. No telling what’s inside. And you’re right about leafcutters. I’ve seen some M. rotundata disasters, all decayed and stuck together with chalkbrood.

  • Rusty.

    While I appreciate the value of the mason bees, they are relentless at finding many new homes in my garage (along with the mud daubers). They are notorious for finding the bore of a pellet gun or a rifle barrel.

    Ron German
    Roca, NE

    • Ron,

      Agreed. I find them in the drain holes below my windows and along the sliding door where there’s a slight recess. I’ve even found them inside outdoor lighting fixtures.

  • I have started setting up cans with paper straws for solitary bees. Do I need to take the straws with dormant bees out of the cans and put them somewhere in the winter where they won’t freeze (i.e. in a garage or shed)? Or can I just leave the straws in the can over the winter? I live in western NC, and nighttime temps are below freezing many nights, just for reference.

    • I think it is best to put them in an unheated garage or shed. It’s not so much about freezing, but about predation by insects, birds, and small mammals. Dampness can also be an issue with paper straws. The stems and burrows where they usually nest are more water resistance than straws, so during the winter you may get mold growth. I just set the can in my shed for the winter and take them back out in the spring.

  • Great article. So, based on your photo, I assume that paper straws work? What’s the best diameter? I’ve heard that bamboo is a problem because of the internodes making it difficult to harvest cocoons. I’ve also heard that bamboo harbors mites.

    • NooBee,

      Paper straws work but they harbor mites just as well as bamboo unless you change them every year. But if you are harvesting from the straws, you will of course be changing them.

      I work hard at finding straws of various diameters, starting at about 1/4-inch.

  • Rusty

    May I add a seventh myth, what I will call the honeycomb myth or the uniformity myth. It’s been over 20 years since I first started raising mason bees. It took a long time to realize that the honey comb uniformity in honey bees deceives almost every one who tries to create housing for mason bees. With every aberration of housing I have introduced (with one exception), I have ended up with healthier bees. More random diameter nest holes, more random natural nesting materials, fewer nests in any one place. I cringe these days when I see enthusiastic honey beekeepers putting out enormous drilled blocks of wood. And yes Rusty (sorry) I even cringe at your packed bundle of skinny paper straws. Yes these systems are tidy mass production but it’s not mass production of success.

    A few years ago I wrote up some observations on housing:
    and wrote 10 rules, that work pretty well:

    It chagrins me that I can no longer do this work hands-on, but I’d be happy to pass some of my housing materials to you. (I’m also sending you an email.)

    Fondly, Glen

    • Hey Glen,

      Don’t think I ever received an email. Hope all is well. My masons are emerging in great numbers and mating all over the place.

      • Yeah I lied I didn’t send the email. Life (chaos) intervened. I’m getting caught up… ha ha ha. This year “my” masons are going to have to find random holes. Meanwhile, I’m going to park myself in front of some Oregon grape that is looking gorgeous, and watch who visits. GB

        • Glen,

          It’s funny that you mention Oregon grape. I’ve been thinking of watching it because so many people say it’s an excellent pollinator plant, but I don’t normally see anything on it. It makes excellent jam or jelly, nevertheless.

  • Rusty,

    I put out several mason bee houses last spring near our garden. I didn’t notice any activity around them, but recently I noticed that many of the “straws” were filled. I removed the straws and placed them into my garage. Should I place them back outside? I live in northern NY state and daytime temps are getting into the 40’s. I appreciate your website…very informative.

    • Don,

      Yes. Mason bees should be emerging about now. Mine have already begin and it’s still in the 30s at night.

  • So, “Do not buy bees”. How, then, does one replenish hives that need bees? I know some people sell nucs who are local, but if you want a package, what to do?? Thanks!

  • I’m interested in building some bee houses with the paper straws, and I see you have soup cans (or something similar) with the straws in them. Where do you place them in the summer for the best results?

    thank you!

    P.S. I found a great deal on paper straws at Oriental Trading

    • Marti,

      Use a sunny location facing south or southeast. I like to put them 4 to 6 feet high, attached firmly so they don’t swing in the wind. Also add a little rain protection, if you can.

  • Rusty,

    I’m so glad I came across your article through a Mason Bee FB page. I picked up a bee house that was on clearance at my local hardware store and then started to research.. Not my normal style but I’m just so excited about moving forward with my honey bee planning phase (no bees yet but maybe next year) that I thought I’d give myself some observational practice this year. Can you provide any tips on housing bees over wasps? Or how to protect your bee houses from birds?

    • Brooke,

      I don’t know what you mean by “housing bees over wasps.” But to protect them from birds you can put the bees behind a fence of poultry netting or something similar that the bees can fly through.

  • 6 April 2019 I have several mason bee questions I have not been able to answer via internet searches. I live in the Central Okanagan in B.C. Canada and this spring has been cold and very late, meaning there are almost no food resources for bees. This has meant people are delaying setting their cocoons outside. So my questions:

    Do mason bees have a biological clock that triggers hatching? Several people who have overwintered their Mason cocoons in the fridge have reported a bunch of bees hatching in the fridge over the past week.

    Is anyone conducting scientific research on the impact of climate change on Mason bees’ reproduction outcomes/populations. For example, if male masons emerge sooner than females and all die because of a lack of food sources this spring, what will happen to the females’ when they hatch?

    Can sugar water be used to feed mason bees?

    Quizzical in Kelowna

    • Kelly,

      I do not store masons in the refrigerator because I believe it interferes with the fluctuating temperatures that most likely signal the bees in some biological way. The one time I stored them in the refrigerator, the population did not thrive as it should have. By storing them in an unheated garage, they seem to be more in sync with weather and temperature patterns. They have evolved over millions of years, much longer than humans and certainly longer than refrigerators, and I believe that natural conditions produce the best outcome.

      For the bees I have in drilled cavities, I don’t even put them inside at all. The ones in paper tubes I put in a shed simply because a paper tube is a man-made product that doesn’t hold up as well as a natural cavity in a raspberry cane or a beetle boring.

      I wrote a post ages ago about climate change, glacier lilies, and bumble bees that may shed some light on your climate change question. In short, plants react more quickly to temperature changes than bees. But as your friends have seen, after a certain amount of time, the bees will hatch regardless of the temperature.

      More resources exist outdoors that most of us are aware of. Many flowers bloom that we can barely see, and the bees make good use of these. Plus, your bees have fat reserves to take them through lean times. You will find that even if the first hatching of males doesn’t make it, more will come along.

      If nature didn’t have this problems sorted out, the many different species would not still exist. Also remember there are a lot of masons bees out there that are not being “raised” by anyone. Some of those bees more than likely will mate with your females when they hatch. This is another reason for going with all native, rather than imported, populations.

      You can try to feed sugar water to masons, although I doubt they would be interested. Your way of looking at their needs is different from their way of looking at them. Try to resist micromanaging, and just let them be bees.

  • Thanks for the advice! Sorry, I should have clarified that I’m worried about getting mud daubers in the bee house instead of wild native mason bees. But looking at your bee houses I think I just need eliminate any open gaps to prevent them. Also, I’m sure it’s not ideal but is it okay to use plastic straws for mason bees?

    • Brooke,

      I get mud daubers on occasion, but I don’t worry about them. They are interesting and don’t harm the masons. I figure a mixed population is a more healthy and natural population.

      As for plastic straws, never. Plastic does not breathe nor absorb moisture, which results in mold growth in the tubes and usually death of the cocoons.

  • Dear Rusty,

    This summer I have had a new kind of mason bee filling the nest tubes in my bee house. Last summer is the first time I put up a mason bee house and had only five tubes filled as this was late June when I put it out. The mason bees I saw, only a few times, were metallic gray/brown. I can’t really remember and did not get pictures, unfortunately. This year the bees have dark black body with bright yellow stripes. They are fairly larger than what I remember. I did get pictures. What species of Osmia are these?

  • Thank you for getting back to me, Rusty.
    I will email you next at your email address and attach photos.

  • I set up a bee house in my garden. The tube ends on some of the tubes became plugged and then had a small hole in the mud.

    When I opened up the bee house I could see where cocoons were started, at least the mud was there, but there were no cocoons.

    What did I do wrong?

    • Small exit holes like that are often a sign of parasitic wasps. If a small wasp got in there and laid its eggs in the developing larva, the eggs would hatch, grow into wasp larvae which eat the bee larvae, and then grow into adult wasps. The adult wasps would then exit through a small hole in the mud. It’s very common and not anything you did wrong.

  • Rusty:

    Thanks for the feedback. I appreciate it. I’m still learning about Mason bees.

    Is there anything I should do different next spring?


    • Tom,

      Most of the problematic parasitic wasps show up just as the mason bees are finishing for the year. I take my tubes (or the whole condo) inside as soon as they start slowing down and store them in an area protected from predators. If the area isn’t bug tight, I wrap very fine fabric mesh around the condo to keep out wasps. You can see cans in mesh in the photo above. The wasps are tiny, like fruit flies.

  • I’ll admit to buying bees in prior years, but on Craigslist from a local individual. I’m guessing that a few miles away is close enough to limit some of the risks you mention. Our garden, and bee houses are on top of a building, and we had limited success starting from scratch. That said, after ‘seeding’ our space we see them return and have no further need to purchase.

    • Bees purchased from a supplier, no matter how local, often come with an infection of mites that otherwise might take years to develop. It results from one species of bee grown in large populations where diseases and parasites freely move from one individual to another. It’s better when bee housing is inhabited by a variety of species that don’t pass on their parasites quite so freely.

  • Hello, Love your website.

    If I was to DIY a condo for the mason bees, what would you recommend? I’ve seen cans and plastic 2-liter soda bottles used. What would you recommend? My concern is also to protect the straws from the elements (rain).


  • Thank you for your very interesting and informative article.

    Question, please. After 3 years, there is activity in my mason bee house that I had purchased at a big box store. I cannot tell whether they are hornets or mason bees. They move too quickly and I cannot get a photo of them. Can hornets live in a mason bee house?

    • Anna Marie,

      Hornets usually live in colonies like honey bees, so they wouldn’t choose a mason bee house. However, certain solitary wasps will live in the tubes and lay their eggs in there, similar to the way tube-nesting bees do.

  • Nobody has mentioned jostling the bees. I just read here or at Olypollinators that the bees are fragile into September. I suspect they shouldn’t be bounced around until after they have grown enough that they can’t fall off their pollen balls. My bee house fell over and I will “get” to see if the bee here were far enough along next year.

    Also, nothing was said about buying commercial bee homes. Some are filled with short bamboo, wide pieces with nodes located anywhere. Avoid those! I called up several places to explain why those were bad for bees.

    I bought two houses from @weebeehouse which were wooden, one with trays, and the other has an observation window behind a door. Both are well made and great to look at, but the bees preferred some wooden logs with random holes drilled in them, or to move back into the too-tiny house that I was trying to get them out of because the tunnels were too short.* One thing I think is that maybe the linseed oil was still too fresh and strong-smelling for them (I painted the observation one myself and only some Halictid males and an earwig try it out).

    The other one was partially filled by the end of the season before it crashed. (My son had wedged it behind a rock, and we thought it was stuck well.)

    A batch of elderberry twigs continues to be ignored, but maybe the bees prefer the actual elderberries closer to the flowers. A house that has been out for at least three years finally filled up. I may have put that one out too late, after the bees were out, the first year.

    I found bees living in holes in an old fence post so I drilled more holes in that and also hung a smaller house I was given on one side. This year it has 4 resin-filled holes and I hope those are Heriades, Resin bees. I also spotted a few tunnels filled with white “cotton” and suspect some Anthidium. I had a bully boy, A. manacatum, terrorizing the Lambs ears, and decided to remove the plant since it isn’t a native plant anyway, and maybe they found another plant to use, but I hope it is a native wool carder instead.

    *Emergence next spring–I suspect that I could have put the too short house into a dark box with a one-hole exit so that the bees would come out and then move into a better home with long, narrow tunnels. “My” bees are smaller than Blue Orchard bees and seem to prefer narrower spaces.

  • Some councils in the UK are specifying that ‘bee bricks’ with pre-drilled holes of different sizes, must be installed in all new houses. Some experts are saying that this will lead to greater disease and pests, as the bricks cannot easily be cleaned. Is this true? If solitary bees use the same holes every year, presumably they are able to clean them out before they use them?

    • Greg,

      This is an area of great disagreement among melittologists. Yes, it can lead to a slow build-up of pests, especially after a number of years. But as you point out, nests in the wild are sometimes used year after year, too. I think we are more likely to see the problems in mad-made nests, whereas we hardly ever get to look into the wild ones. That doesn’t mean the problem is greater in mad-made nests, but perhaps only more evident.

      Others argue that native nesting areas are becoming scarce, so the extra housing outweighs the problem of parasite load. I agree with this latter group. I think it’s better to do something than just let the bees languish due to a shortage of nesting space.

  • Great site! I am curious. We are building a greenhouse for growing vegetables and fruits indoors during the winter in particular. I am close friends with Kaitlyn Culbert who just won a NJ award for bees among others. I had planned on employing mason bees inside and out. But their short life may make that impractical. Ideas? Ideas for other pollinators good for inside a greenhouse?

    • Gregory,

      It depends on what plants you want to pollinate. The classic greenhouse pollinators are bumble bees that seem okay with the confinement. They also pollinate quite a few different plants, which can be helpful if you have multiple crops. An individual bumble bee doesn’t live any longer than an individual mason bee, but since they live in a colony, new bees emerge all season. You can buy bumble bee colonies for the purpose.

  • Hello, I have a large garden and orchard with mason bee houses. I had a prolific spring with intense mason bee activity and they filled up all the nesting holes. Shortly afterwards I started to note holes in the mud and then some of the tubes had larvae, pollen and mud missing. I thought maybe earwigs were a problem but I did not see them. Then I thought maybe ants? I got concerned and thought perhaps something was climbing up the post at night and feeding on the larvae. I brought them into the garage to get them off the post. I opened up a tray and I see a lot of black mites. There seems to be more tubes that have been opened. I still see lots of larvae but I am concerned the mites are harming the larvae. I would super appreciate any ideas as I do not want to lose my hive.

    • To me, it sounds like parasitic wasps, but I can’t tell for sure from here. When you say mites, did you you look at them close up? Are they larvae (insects), nymphs (mites), or adults? If adults, do they have six legs or eight? Do they have wings?

      Also, sometimes birds poke into the holes to get the baby bees, but it could easily be other insects. The worst parasitic wasps, Monodontomerus, look a lot like fruit flies. A bad infestation of these can wipe out the entire community of mason bees.