The horrors of mass-produced bee houses

Here are some reasons why cheap mason bee houses can end up hurting bee populations. I live in Pennsylvania (USA), so some of the issues might be specific to my location. And to the species that live here, of course. Check with your local authorities for more detailed advice.

1. Nesting blocks, tubes, reeds are not removable

Glued nesting materials is the number one reason why most commercial bee hotesl can become death traps. Because the nesting material cannot be removed and cleaned, over time there will be an increase in the population of parasitic wasps, parasitic bees, parasitic flies, kleptoparasitic mites, fungi, bacteria, and viruses. And you typically won’t see these dangers because the solitary bees will still use the hotel (they can’t help themselves). Here’s a photograph of the mites that tend to build up when bees reuse the same house every year. Sometimes they have so many they can’t fly anymore.

Hundreds of Krombein’s hairy-footed pollen mites on a mason bee. Image by @GeeBee60.

Ideally, empty out the house every year or two and give it a good cleaning. You can do this by removing all the filled nesting tubes at the end of the season (e.g., October) and storing them in an unheated garage or shed. Then, in the early spring put these nests inside a cardboard box that is equipped with a small exit hole — so bees can escape but can’t re-inhabit the nests. Finally, once everyone has emerged, clean the trays (brush, wash with bleach), re-drill holes (for blocks), and throw away reeds and paper tubes. While all this is happening, equip your (cleaned) house with fresh nesting trays, blocks, paper tubes, reeds, etc. All of this can’t happen, of course, if everything is glued in place.

If the above sounds like way too much maintenance, perhaps don’t buy a mason bee house. Get a garden gnome or a gazing ball.

2. Nesting tubes cannot be opened

Even if you clean the house every year and put in fresh tubes, the tubes filled in the prior year might be filled with parasitic flies and wasps. The ONLY way to get rid of them is to pry open the tubes and examine each pupa. And you can only do this if you use paper straws (that you can unwap) or if you use routered nesting blocks (that can be taken apart). So if you want the best accommodations for your solitary bees, opt for either of these designs.

3. Nesting tubes open at back

If holes aren’t capped in some way at the back, parasites can easily gain entrance. Mason bees will plug the back with mud but it’s best to have a wall.

4. Reeds or holes with large splinters

Sharp edges inside the holes can snag and tear delicate wings.

5. Stems blocked at front

In houses that use bamboo, sometimes many of the sections are blocked off near the front by an impenetrable node. E.g., many of the tunnels are too short to be of much use.

6. Tunnels are not the right diameter

If reeds or bamboo are used in the house, make sure that they are all the diameter that supports the species of bee you want to attract. Solitary bees will end up using tunnels that are too wide but they will waste mud (and time and energy) filling them up. Bamboo houses are often a problem in this regard. (If you want to attract all different types of hole-nesting insects, then diversity in diameters is fine.)

7. Roof lacks overhang

Mass-produced mason bee houses are designed to be as compact as possible so they can be packed and shipped efficiently from factories in Asia. This usually means that they won’t have roofs that protect the nest entrances from water. Moisture causes larvae to rot and also seems to cause kleptoparasitic pollen mites to flourish. If your house is fine except for the roof, get creative and attach one. Or stick it someplace that is under a pre-existing structure.

8. House attaches to tree with string or hook

Mason bees start their lives as eggs on top of a mound of pollen, and houses swinging in the wind could cause them to fall off or be crushed by moving pollen balls (when too dry they can shift). At least that’s the word on the street. Perhaps a more important reason to keep the house stable is that mason bees likely find it challenging to land on a moving nest. If you have a mason bee house that is designed to hang, just get creative and attach it somehow so the bees have an easier time landing.

9. Nesting material is impermeable to water

Like anything that’s alive, mason bee eggs, larvae, and pupae produce water during respiration. When that moisture can’t escape the bees are likely more susceptible to bacterial and fungal pathogens. Plus the pollen ball itself can rot. So avoid houses that use plastic, glass, or metal tubes.

10. Nests are too shallow

The house pictured at the top of the page is approximately 2″ deep, and that could lead to most of the progeny being males. In nature, mason bees lay fertilized eggs (which develop into females) at the backs of long nests, then pack the front with unfertilized eggs (which develop into males). This means that houses with short nests can end up being primarily nurseries for worthless guys (sorry, guys). If you want a house that can generate an ecologically useful proportion of females, buy houses with nesting tubes that are approximately 6″ (152 mm). Having shorter tubes (say 4″) might be OKish but you may have far fewer females. Shorter tubes are of course fine for smaller species of solitary bees that live in smaller-diameter tunnels.

11. Contains pine cones and other fillers

Solitary bees don’t utilize pine cones. Companies cram them into insect houses because pine cones are cheap and people generally regard them as chic. The only thing that seems to be common in pine cones out in the wild are spiders. Similarly, cramming moss, bark, pine needles might be evocative of nature and visually pleasing, but they do nothing for the bees as far as I can tell.

12. Contains holes that lead to empty cavity

This is yet another way to save money. Solitary bees use tunnels, not rooms.

13. Contains slits for butterflies

Solitary bees will not use these slits and neither will butterflies. Again, companies incorporate them to save on wood and labor, plus to influence buyers who are fond of butterflies. Don’t be fooled.

14. Honey bee shown on packaging

A photograph of a honey bee on the label is a likely sign that the house is probably not up to code. I.e., if company doesn’t know the difference between honey bees and solitary bees the house is likely to have multiple design flaws.

Mason bee house with honey bee drawing

15. Too many nesting units

When thousands of mason bees are living in close proximity, parasitic insects and mites can easily find every nest. I also predict that Asian giant hornets (Vespa mandarinia; aka “murder hornet”) will eventually learn to attack bees at these large mega-complexes. If your heart is set on an eye-catching mega-complex, just be extra sure that all components are truly cleanable or disposable. It’s also critical to actually clean it, too, so don’t buy it if you’re the type that doesn’t like to do that sort of thing.

These look soooo cute, but if ALL the blocks are left in place for multiple years they become towers filled with bee parasites.

16. Inadequate instructions

Even if you buy a good bee house and generally know things about the needs of solitary bees (mud, leaves, lots of native plants, etc.), you can still benefit from detailed instructions from somebody who thinks about solitary bees all day long. E.g., look for instructions that tell you how to clean the hotel in between seasons.

Flow chart for making buying decision

Here’s a summary flow chart to print and keep in your wallet so you’re prepared when you see something adorable. Or print and give to that shop owner who carries trap houses.

“OMG I own a death trap what should I do?”

If you have a cheapo mason bee house that saddens you, don’t do anything rash. Just leave it up and let your current residents do their thing. But at the end of the season, after all the holes are filled, put it in an unheated shed or garage for the winter (so that birds don’t feast on the pupae). In early spring, put the whole house inside of a cardboard box (here’s an image of durable emergence box). Poke a small hole in the top or side so that emerging bees see the light and escape through that hole, and then set it outside in a place where it will stay dry. After all the bees finish emerging (summer), throw out the house. Or, better, burn it and record a video of the fire. Then post the video online to bring needed awareness to low quality mason bee houses. If you have a good photograph of a burning mason bee house, I could use one right here.

“I want a cute bee house but not the commitment”

If you want the look of a bee hotel but don’t want all the maintenance fuss, print this photograph onto a large piece of paper and mount onto a board. Neighbors will think you have the real thing. To make it last, laminate or apply a coat of clear varnish.

Free bee housing for the lazy

The BEST way to encourage lots of native bees in your yard is to just stop overdoing the yard work. Make a pile of stems from last year’s perennial garden somewhere in yard, and they’ll naturally break apart and be found by solitary bees — Monarda and Asclepias are some of the many perennials that are hollow. And leave dead trees (or logs) so that boring beetles do their thing and leave nice tunnels for the bees. Finally, leave some patches of your flower beds unmulched so that ground-nesting bees have some ground.

More information

Don’t let the above discourage you from owning your dream house: here’s a draft listing of companies that make good ones. Or, make your own. Below is the one in my front yard.

16 thoughts on “The horrors of mass-produced bee houses

  1. Cat Cameron-Pazera

    Thank you! I got a big, wooden bee house from Costco. It won’t be used after this year (unless I can get the bamboo out), and I’ll bee sure to follow your advice in the future.

    Can I use sunflower stems as bee houses?

    Reply
    1. Toni Stahl

      This is a great article. Here is an idea: Nature’s Best Hope, the book by Douglas Tallamy, recommends building a few small Houses, with 4 or 5 tunnels each, and scattering them in different places in our yards. I also read a 3-year study you might be interested in that concludes that wasps occupy almost 3/4 of the house: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0122126. Have you had problems with wasps? Will you email me your thoughts? Thank you.

      Reply
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  6. Sheila

    I did buy a Costco beehouse last year. A few of the tubes had the ends masoned and in the Fall I placed it in the unheated garage. Now I don’t know what to do. The tubes are solid in there and so there is no through way…Now should I try and poke the dried masonry mud out or just leave it and hope for the best ?

    Reply
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  10. Kristina

    Hello Colin,

    This post, features some products for which I manage for my company in your photos . I wanted to reach out to you, since our product was in the photos to explain how we have improved our product offering over the past year and a half. Below you will find my response to each of the call outs that were made about how mass produced bee habitats could be killing the bees. You will also find in my response how we as a company have strengthened our knowledge in what are the best practices for developing and producing our bee habitats.

    1. Nesting blocks, tubes, reeds are not removable AND 8. Nesting material is impermeable to water
    – We offer a variety of different types of nesting tubes for our customers. We have been offering primarily bamboo tubes up to this point. Last year we introduced a removable tray design, which we saw a lot of interest in. Therefore for this year we are expanding on the removable tray designs as well as introducing a paper/cardboard tube style. We have written up training materials for our retailers and end consumers, in order for them to be well educated on the how to’s. For all styles, but specifically styles with bamboo tubes, we emphasis the importance of cleaning the habitat after each season. We have started recommending that each customer purchase 2 habitats so that they can be switched out between seasons. We found that this was helpful to limit parasites.
    2. Inadequate instructions
    – In October 2017, we purchased a company who was offering bee habitats to end consumers and key accounts. With this acquisition, we learned a lot about bee and insect habitats from our colleagues. One of the things that we learned was the importance of adequate and detailed instructions. With our new release, we updated all of our habitat packaging to include instructions, tips, and why. Since this change we continually enforce the detailed instructions on all of our new habitat designs and current.
    3. Nesting tubes open at back
    – All of our designs have a back wall to cap off the back of the nesting tubes.
    4. Reeds or holes with large splinters AND 5. Stems blocked at front
    – We have recently consolidated our bee and insect habitats to a main source for producing our products. This vendor is professional in bee habitats and is actually a vendor for Costco’s bee habitats. We are consistently doing quality checks of the product and audits of the products to ensure there are no issues, such as blockage of the nesting tubes or sharp edges.
    6. Roof lacks overhang
    – All of our current designs and new designs have a roof overhang to protect the nesting tubes from climate.
    7. House attaches to tree with string or hook
    – All current and future bee habitats that we offer must be mounted.
    9. Nests are too shallow
    – All of the designs that we currently offer and will continue to offer in the future have tubes that are at least 5-6″ deep to allow for female bee eggs.
    10. Too many nesting units
    – We do not and do not plan to offer large multiplex habitats. We do offer small scale multi habitats but emphasize the importance of cleaning after each season.
    11. Honey bee shown on packaging
    – Several years ago, the manager at the time was not aware of this. We have since updated our packaging (see point #2) and our knowledge on mason bees.

    I hope that you can see that we are trying to do the right thing and help the bee population. We hope that we will gain your support with all the of updates that we have made to our product offering.

    Thank you for your time.

    Reply
  11. Brenda

    Kristina, Thank you so much for your post.
    I purchased the following book: A GUIDE TO NORTH AMERICA’S BEES. JOSEPH S. WILSON & OLIVIA MESSINGER CARRIL. PRINCETON UNIVERSITY PRESS-PRINCETON AND OXFORD. $35

    The book shares how to build bee houses.
    Thanks, Brenda

    Reply
  12. Brenda

    Kristina:
    I recommend this book: A Guide to North American Bees. Joseph S. Wilson & Olivia Messinger Carril
    PRINCETON UNIVERSITY PRESS PRINCETON AND OXFORD

    I purchased one a few years ago for $35 The book contains instructions for bee houses.
    Brenda

    Reply

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