mason bees

Upright hollow stems: much better than toxic mason bee houses

A reason for using upright hollow stems for bees: This western blue orchard bee with mites. Photo © Briana Lindh.

Toxic mason bee houses come from too many bees living together in a small area. To help the bees social distance, we can leave upright hollow stems in our gardens. Photo of western blue orchard bee with mites © Briana Lindh, Salem, OR.

Inside: Many solitary bees living close together provide a leg up to all the predators, pests, and pathogens that plague cavity-nesting bees. Upright hollow stems provide a healthy alternative to crowded conditions.

We all think, “It won’t happen to me. I’m careful, so my mason bees won’t have any health problems.” Trouble is, nature is an opportunist. If an organism sees a chance to thrive on the back of another, it will.

The rise of mason bees

In the last twenty years, orchard mason bees have exploded as household pets. They are often impulse buys, purchased after seeing a cute birdhouse-like mason bee condo in the aisle of a favorite store.

No doubt, mason bees and their close relatives the leafcutting bees are pollinating superstars. They are fast and diligent, pollinating many flowers and crops. And if you keep them in an easy-to-see location, they are mesmerizing to watch—much easier to view than honey bees inside a hive. Even better, they hesitate to sting and rarely confront a passive bee-watcher.

Unfortunately, lots of mason beekeepers have a “set it and forget it” mindset, a philosophy that seldom works long-term. Eventually, untended bees will die or move away.

Congested quarters can be deadly

As with many other creatures, large groups of mason bees become bait for organisms that can take advantage of them. The number of threats to cavity-nesting bees like mason bees and leafcutting bees is enormous. The list includes multiple types of mites, wasps, birds, fungi, molds, and pathogens.

These threats occur naturally in the environment, appearing pretty much everywhere. But as the pandemic reminded us, when individuals live and work close together, diseases spread like wildfire, fast and furious. Parasites and predators also delight in finding a cache of closely spaced victims and will pounce on the goldmine of nutrition the bees provide.

Even though many of the solitary bees are gregarious by nature—often living close to one another—they don’t live as tightly packed as they do in a bee condo. They naturally spread further apart, making each one safer from the things that might attack. A bit of social distancing goes a long, long way toward solitary bee survival.

Unlike honey bees, solitary bees need space

After seeing honey bees and social wasps living in massive colonies, we might assume dense living is normal for bees. But unlike solitary mason bees, social insects like honey bees live in colonies with multiple defenses against invaders.

Just as a herd of elk, a school of fish, or a flock of birds have crowd-sourced safeguards, so do colonies of insects. Often their defenses involve the sacrifice of some for the good of the group. But solitary bees are more like rabbits or moles or woodpeckers: their defense mechanisms don’t involve others. Even though solitary bees may live near members of their own species, in most cases they must defend themselves.

Like anything worthwhile, mason bees require effort

Unfortunately, there is more to raising mason bees than hanging a bee house on a post and walking away. Those cute miniature houses can actually be death traps, luring young solitary mothers to nest in a pit that attracts diseases and predators. It’s hard to imagine anything more ingeniously designed to fail.

Not only do dense bee settlements attract disease, mold, and fungus, but those woodpeckers, parasitic wasps, and mites also admire them. Sadly, most things that go wrong with mason bees go wrong right in their own home.

Yes, you can successfully raise mason bees in condos, bee houses, and drilled blocks, but it takes lots of effort. In addition, the various steps need to be addressed on time before the attackers win. It’s easy to forget a step or be late, or you may not enjoy it enough to keep going.

Remember all those people who got pets during the pandemic, and then turned them into a shelter after a year or two? It’s the same with mason bees: all the fussy, repetitive work could cause you to question your decision.

The progression of mason bee problems

The progression of mason bee problems usually follows a predictable pattern. When someone gets their first mason bee house, everything goes well for the first year, or sometimes even two years. If you’re lucky, your purchased mason bees didn’t come with many pathogens, so the first round of bees emerges, mates, and fills those new tubes with pollen and eggs.

But somewhere in their travels, the bees pick up pollen mites. So by the second year, there may be some bee losses caused by mites, and you may even find bees covered with thick layers of pollen mites. If the beekeeper doesn’t clean or change the nesting tubes in time, the bees lay next year’s bees in the contaminated holes. When that happens, beekeepers often say, “Oh well. They’ll be fine.” But they won’t; infestations rapidly get worse.

Also, after the first season, the local fauna has had time to discover the location of your bee community. Often by the third year, parasitic wasps hang around in great clouds. The worst of these, like Monodontomerous, are smaller than a fruit fly. But don’t be fooled: they are treacherous. They will lay their eggs inside the bee pupae. Then, when the wasp babies hatch into larvae, they will eat the developing bee from the inside out.

Hollow Stems vs Pithy Stems

Mason bees and leafcutting bees generally like hollow stems, but some bees like stems with soft, pithy centers. Those bees, including many of the small carpenter bees, chew the pith into a paste to use for building partitions between egg chambers.

Upright hollow stems: an alternative to bee condos

Growing plants with hollow stems is a healthy alternative to manmade bee housing. These are the types of nests cavity-nesting bees would choose if they were living in the wild. Several characteristics make upright hollow stems the very best bee housing.

First, the stems are spread further apart. In each bunch, a few may be close. But for most, there will be inches between each one. Also, the bunches themselves may be spread across inches, feet, or even yards.

The greater separation between nesting tubes makes it more difficult for diseases to spread and it makes it harder for birds and wasps to find them. In addition, birds can’t stand in one place and eat for hours. Instead, they must keep hunting, poking, and finding places to alight. The entire process is more difficult and time-consuming.

Another advantage is that the stems naturally fall over and begin to decompose after a couple of years, perfect timing for raising healthy bees. The latest generation of bees can still emerge from the toppled stems, but the current adults will not nest in them, so it’s a natural, no-effort cycle that keeps pathogen levels low.

Nature has this all worked out, yet we humans think we can do things better. But sometimes, that just ain’t so. The biggest drawback to using upright stems is the amount of long-term planning it requires.

How to grow upright hollow stems for your bees

Year One

  • You must choose the right plants for your area, so you may need to consult your extension agent or local garden club for advice. You need plants that have either hollow or pithy stems. Some examples include lovage, elderberry, blackberry, teasel, drumstick allium, mountain mint, goldenrod, sunflowers, joe-pye weed, and swamp milkweed.
  • At the end of the first growing season, cut the stems back to roughly 12 to 18 inches high. Using a sharp tool, try to make cuts smooth and straight for an attractive, non-threatening nest entrance.

Year Two

  • During spring of the second year, cavity-nesting bees will use your upright hollow stems to build their nests. Leave these standing all year. Some species may produce brood late in the summer of the same year, but most, including your mason bees, won’t emerge until the following year.
  • Also during the second year, you can start more plants for the next season, especially if you’re using annuals. Remember to cut the hollow stems back to 12 to 18 inches in the fall.
  • In the late fall or early winter, some stems will remain standing but some may bend over or fall to the ground. Some people like to leave everything natural, not disturbing the stems at all; others prefer to cut the stems at ground level and store them in a cool, dry place just as you would bamboo tubes or paper straws.

    Either way is fine, but if you collect the stems, be sure to put them in an emergence box in the spring so the bees do not reuse the old stems. (Note: if you live in an area with wet winters, collecting the stems is better.)

Year Three

  • In spring of the third year, bees in your first planting of hollow stems will emerge and many of them will nest in the stems from your second-year planting. Now you’re on a roll. You just have to keep going and you should have plenty of healthy bees to pollinate your orchard and garden crops.

Healthy bees are worth the effort

I hope you give this rotation a try. It sounds like a lot of work, but done properly, it can eliminate harvesting and bleaching cocoons, which is boring, time-consuming, and not natural at all.

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About Me

I backed my love of bee science with a bachelor’s degree in Agronomic Crops and a master’s in Environmental Studies. I write extensively about bees, including a current column in American Bee Journal and past columns in Two Million Blossoms and Bee Craft. I’ve endured multiple courses in melittology and made extensive identifications of North American bees for iNaturalist and other organizations. My master beekeeper certificate issued from U Montana. I’m also an English nerd. More here.

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  • I have always wondered about the horizontal tubes used in ‘bee hotels’. Surely in nature, vertical stems would be the norm, not horizontal? Do the bees go in from the top of the stems, or make holes in the side? If they enter from the top, doesn’t rain get in?

    • Greg,

      Most of the stems are not perfectly vertical but lean one way or another, but I think rain would get in. The bees go in the top, not the sides. Whenever I’ve seen bees using them, they behave the same as they do with horizontal stems, that is the female goes in head first, checks on things, comes out, and then backs in with her pollen load. Busy, busy. Honestly, I don’t know what they do with rain.

  • Many of those hollow/pithy stemmed things grow all over my area. All we have to do is quit mowing enormous stupid lawns.
    Also, not that I’m succumbing to any suggestion that I do work, but what do you cut them back with? I just wish my lawnmower would cut 6 inches high, but 12 to 18 seems totally impractical. You mean hand-cutting. I look at you with the same blank expression I use whenever anyone suggests hand-sewing.

    • Hey Roberta,

      What are those hollow/pithy things you have growing all over? I’d really like to know because people always ask me what plants work for tube-nesting bees. Are your plants sturdy enough to last a couple of winters?

      • Just from your list and internet pictures, I’m pretty sure there’s at least lovage, elderberry, blackberry, teasel, goldenrod, sunflowers, and joe-pye weed around me. (Of course with my astonishing taxonomic skills, the only thing I can swear to is that they’re not honey bees.)

        Much of it is being managed as hay fields, so cut short at least once a year and possibly not a good place for tube-nesting bees, but there’s a lot along the road that doesn’t get cut at all if the bees can make their own entrances. I know I have goldenrod and blackberry (which I can’t tell from multiflora rose unless there are roses and I pull it out to no avail or berries and I eat ’em and encourage them) in my own yard which don’t get cut at all, so the bees would have to make/find their own entrances.

        The only times I’ve ever seen a huge group of tube-nesters all together on my property, they were hatching out of the woodpile, which would get burned about every other year—so brought in with the wood? Hatch and lay eggs that hatch and lay eggs that hatch but the babies are burned? I think they might be better off staying away from humans entirely, if only that were possible.

        Also, it’s only April, but I’ve already started No Mow May. (Or else I’m just lazy.) I have beautiful dandelions and Jill-all-over-the-place. I think I actually saw a honey bee on the Jill/Creeping Charlie. The bees I’ve seen the most this spring are the carpenter bees. I hatesss ’em, my preciousssss. But I don’t do anything about ’em. They’re saved by laziness.

        Also, if the unassisted bees lay eggs in pithy hay meadow plants, can they survive the haying and hatch out of the hay bales later (before the hay is used)? Can they survive if the meadow is mown and the pithy stems and all are left where cut?

        • Roberta,

          Survival is a numbers game for most species. So I think yes, some of the bees may survive having their tube cut and laying on the ground, and some may survive being tied into a bale and shoved in a barn. Not many probably, but some. That’s one way invasive insects get spread: they survive against all odds and wake up on another continent. Insects, including bees, are amazing.

  • Hi Rusty,

    I have hollow-stemmed plants that are the right size for the smaller leafcutter bees, but I have not been able to find any plants with stem sizes that mason bees prefer (7-10 mm diameter). All the plants I research seem to be either too wide or too narrow, or often just don’t have information available online about their stem diameter. Which of the plants you listed (or didn’t list) have you found mason bees to use the most?

    • Bob,

      The stems I like the best for mason bees are lovage. But you can only use the smaller diameter ones. The largest are too fat at the bottom. Blue mason bees also like blackberry canes, but again only some are the proper size. Teasel works and the stems are pretty much uniform.

  • But these are solitary bees and there’s only a small number at any one time in a mason bee nest. Unlike honey bees that can have 10s of thousands in a hive.

    Mites can be transmitted from external sources. Beekeepers have learnt how to control the parasitic varroa mites on honey bees down to a manageable level.

    Horizontal tubes are less likely to get waterlogged.

    • Tony,

      Many mason bee and leafcutter bee installations have hundreds of thousands of holes. See the leafcutter domiciles on this post. Yes, mites can be transmitted from outside sources, another reason to keep mites in check so they don’t spread. If your bees have mites, the mites can drop onto flowers where they can infect other bees.

      Beekeepers do manage varroa mites, but only barely.

  • This is just a curiosity, but if I was to take a 3d printer and create a base that I could plug various reed tubes into it at different angles then make a little roofing compartment almost like a wishing well design do you think this is something that could realistically work or again to back to the root problem you mentioned above?

    • Justin,

      Some people are experimenting with making the cavities in bee houses less compact. Some are spacing drilled holes further apart, and some are using dummy tubes with no opening in between usable tubes. A few people I know report good results. So yes, I think your idea has merit and it’s probably worth a try.

      If you build it, please send a photo! I’m curious what you come up with.

  • I haven’t purposefully tried to leave these cultivated plant stems upright for my mason bees, but I have discovered and prepared them to use for a natural reed in the nesting box: dahlia and pampas grass. They both get used and are easy to harvest cocoons from if that’s how you do. I can’t imagine how any stem nester would survive in an upright stem here in PNW, but I understand several species are native here. I wonder how that works…

    • Paula,

      Several years ago I had a red elderberry in my backyard that I cut way back. Before long, small carpenter bees (Ceratina) were nesting in the perfectly upright stems. I watched them work at that for several weeks and then, all winter long, I thought about them getting pounded by the rain. Come spring, I netted some of the stems to see if anything emerged and, sure enough, the carpenters appeared almost exactly one year from when I first saw them.

      My theory is that the glue they make with saliva and pith is pretty much waterproof, but I never dissected a tube to actually look at it. Something similar happened with some blackberry canes I left in place. I didn’t see anything nesting in them, but I did see things emerging from them in the spring. I would like to know more.

    • Jessica,

      Many people, including me, are against shipping mason bees (and their disease organisms) from place to place, but I know lots of people prefer to do it that way.

  • My husband and I love pollinators but we don’t have the time to babysit anything other than our 3 kids. As much gardening we do we are during the week 30 min to an hour gardeners. So keeping bees is not something we can do with our time constraints. We will be planting hollow and pithy stem plants for solitary need but is there any way to encourage a wild hive of honeybees to consider our garden a good place to forage? We plant beans and peas in large quantities as our kids love them so no problem with flower fidelity. We have wood bees and some solitary wasps that we know of but we also know that most pollinators are much smaller than we can easily see. Any suggestions for encouraging the bees?

    • Brianna,

      Honey bees prefer nectar that is very high in sugar because they must make honey from it. But flower preference is very much dictated by local conditions and what else is in flower at the same time. You may have to experiment or ask a local beekeeper what works well in your area.

  • A question about mason bee houses: many websites suggest orienting them to get morning sun, but isn’t that unnecessary since they will only be holding newly laid eggs? (Or is this advice only for bee houses that stay in place all winter?)

    • Pat,

      Morning sun warms the bees letting them know it’s time to forage. Often the adult female will sleep in the end of an unfinished tube of eggs, so the sun would benefit her. Also, sun-warmed tubes of bees (as long as it’s not super-hot) are less likely to grow mold inside the tubes.