bee hotels, invasive bees, bee conservation

Bee hotels – the good, the bad, and the ugly

Bee hotels are very popular at the moment. Everybody sells them, often with the popular “save the bees!” attached to it. But are they really worth the hype? I’m not that convinced, as you may already imagine. Let’s start with the positive: insect hotels are a nice way for people, especially children, to learn about bees beyond honey bees. I’m very convinced of the saying “you only can save what you know”. Trap nests, as they’re also called, have the additional charm of being engaging: you can do them yourself. By doing so, you also learn about the cavity sizes different bee species prefer, about the species that may nest there, which materials to use etc. A perfect way of learning by doing.

I’ve always seen bee hotels as an educational tool. The entrance to the world of bees – which is a big thing, I definitely don’t want to belittle this. But there’s a caveat: you don’t “save the bees” with them. By the simple reason, that trap nests give a home only to a small fraction of bees. Most bee species nest in the soil. Bees nesting above ground and using cavities like those in insect hotels in Germany make only about 14% of all species. Let that sink in for a second.

Bee hotels aren’t always helpful

My biggest criticism of the “Save the bees!” movement is – this shouldn’t be a surprise – the massive simplification. In general, it means honey bees. I won’t go into this issue, I discussed it extensively already. Some understood that it’s the non-managed bees that are most in danger. But here comes the next simplification: they step into the bee hotel trap, which isn’t very helpful, too. Especially, as you see them everywhere now. With the abundance of offers, come also those who just want to profit from the trend. Many of the insect hotels sold in garden markets, DIY stores or similar places are death traps: the borings, stems etc. have frayed edges. This can injure or kill the animals. Not exactly what people mean by “saving the bees”, isn’t it?

Simplification is harmless at best, but sometimes – like in this case – harmful. Like the Austrian philosopher Rober Pfaller said:

Everything is miserable as long as you don’t know how to do it. This applies to wiping off sticky liquids as well as to comforting desperate friends.

From the book “Wofür es sich zu leben lohnt: Elemente materialistischer Philosophie” (What it’s worth living for – elements of a materialistic philosophy), from Robert Pfaller, 2012. As far as I know only available in German.

Despite my amateurish translation, this is also true for “saving the bees”. Which I can’t write without quotation marks, I’m sorry. You have to know what you’re doing. And how to do it, depending on the species and habitat you want to work on. None of the over 20,000 bee species worldwide is exactly the same. They all have different life-histories and needs. The paper I discussed in my last post, states this very clearly: pollinator conservation fails because of the lack of specific actions.

Bee hotels and invasive bees

Having ticked off the good and the bad, now let’s come to the ugly. A recent paper extensively discusses the effect of trap nests on the invasive Giant Resin Bee (Megachile sculpturalis). I’ve seen this species the first time in 2016, in the garden of the Apicultural Institute in Bologna. It’s an impressive bee, but I was less excited when I noticed that it was an invasive species. However, Geslin et al. wanted to investigate the belief that bee hotels serve bee conservation in general and specifically their use by M. sculpturalis.

They analysed 71 insect hotels in twelve parks in Marseille (on the Mediterranean coast of France). They then analysed how many species and how many individuals of each hatched in the following year. The results are worrisome: from the 889 individuals that hatched, 356 were the Giant Resin Bee. That’s 40%, the majority. The second-most abundant species was the Red Mason Bee (Osmia bicornis, 34%), followed by O. cornuta (16%), O. niveata (7%) and O. caerulescens (2%). All mason bees, all native, but not typical Mediterranean species, and except O. niveata none of them endangered. What already covers the aspect of “bee hotels as a conservation tool”. In addition, the invasive and the native species co-existed only in ten of the bee hotels. Geslin and his co-authors found that the more the invasive species was present, the less likely it was the native species could hatch.

A dead carpenter bee in front of a bee hotel in the garden of the CREA-AA in Bologna. Laura Bortolotti and her team are studying the impact of the invasive Giant Resin Bees (the flying one…) on native bee populations.

Competition for nests and aggressive behaviour

There are several points in this paper that relate to the “saving the bees” issue from the beginning. The number of species is quite low and the invasive Giant Resin Bee is the dominant one. This is a problem: Invasive bees not only may transmit diseases but may also disrupt the pollinator-plant network. IPBES considers invasive species one of the reasons for pollinator decline. In particular, M. sculpturalis is also known for its aggressive behaviour towards other bees – both of the same and other species. They “clean out” other nests as well to use the cavity themselves.

Geslin and colleagues say that this behaviour can’t explain their findings: the native species they found, nest in smaller borings than the invasive one. On the other hand, another colleague studying these bees, Laura Bortolotti from the CREA-AA in Bologna, made different observations. They observed five dead carpenter bees (Xylocopa violacea) in a bee hotel where Giant Resin Bees were nesting as well. Carpenter bees are much larger than the mason bees in France; they nest in similar sized cavities like M. sculpturalis.

Do you see? The conditions were different, and, therefore, also the observations. In Marseille, the trap nests were “new”, they observed the bee population after the first year. In Bologna, when the invasive bee species appeared, there was already an established population of different bee species in the garden of the institute. The impact is different, depending on the circumstances.

Bee hotels are a tool

There would be much more to discuss considering bee hotels and their value to bee conservation. This is becoming an increasingly studied area, fortunately. Especially, like gardens and other urban spaces are getting into focus. My point is that insect hotels are a tool, not more and not less, in the toolbox for bee conservation. This shouldn’t discourage you. I’m not saying to dump everything you have in your garden. However, perhaps don’t aim to “save the bees”. Just do what you can. If this is planting a few flowers, having a bee hotel on your balcony – go for it.

Yet, be aware of the limitations. There’s no one-fits-all solution. Try things out, inform yourself, modify if necessary. In this context, I’m planning to offer consulting of bee-friendly gardens together with a gardener and architect friend. We’re splitting competences here (I don’t know everything after all…). If you have any questions in this area, let me know in the comments. I’m already doing this for agricultural context for a while now, but gardens – again! – are different. So we will have to think everything over and adjust it for these special circumstances. Your questions will help to make it a good service and to bring it to life.

28 thoughts on “Bee hotels – the good, the bad, and the ugly”

  1. I really enjoyed this article, thank you. You asked for gardening questions at the end. I suppose my main question would be what gardeners can do for ground-nesting bees, especially in small gardens. Is it possible to recreate nesting habitat in even the smallest of spaces? And if so, what would be your recommendations? Thanks

    1. Claudia Garrido

      Dear Ben, thank you for your feedback, I’m happy the article was interesting to you. Creating nesting habitat for ground-nesting bees can be as simple as leaving small patches without vegetation, like on paths. We’ve had nests between the stones of the footpath to the house, and – especially popular – the edge between the path and the meadow. If you want something that’s easier to observe: people have been trying out cutlery trays from the big Swedish furniture shop… (I don’t do advertising on this site, but I guess you know who I mean) filled with clay and sand. You could follow @grassroofco on Twitter, who has good ideas like this one:
      Have a nice weekend!

  2. Thank you for this thoughtful and thought-provoking article. I’m a gardener (Vancouver, Canada) and am trying to make my (small) gardens more supportive of pollinators. I’ve been considering taking the next step and attempting to accommodate bee nurseries, but am feeling quite uncertain about the best way to go about it. I have little space, but I can be creative. Your comments are useful as I try to inform myself how best to proceed. So thank you again.

    1. Claudia Garrido

      Thank you, Mael! Also for being supportive for pollinators in your garden. It’s possible also in small spaces. Perhaps you could contact a local association for help? You could try also some structures like the one I recommended to Ben in the other comment. An earth path with some gravel creating some boarders between areas with and without vegetation may be an option for you as well?

  3. Hilton Unsworth

    Lots of old discarded hosepipe is discarded and sent to landfill on a regular basis. Would it be appropriate to cut this up for use insect houses? If not, why not? H

    1. Claudia Garrido

      Thanks for your question! I don’t think hosepipe is appropriate for insect houses. For several reasons:
      1. The diameter of hoses generally is quite large. Most insect species that use cavities like this need smaller diameters – the largest being around 8-10mm.
      2. The plastic material isn’t appropriate. It doesn’t absorb moisture (it’s made for the contrary, after all) which could lead to mould and kill the larvae/destroy the food provisions.
      3. Plastic has a variety of additives (softening agents etc.) that may be toxic for insects or disturb their development.
      I understand the thought behind this question, it would be a nice “upcycling” of material otherwise discarded. But for this specific material, the solution must be different than building insect hotels.

  4. Richard Taylor

    We found your article very interesting. Over the last five years we have been redesigning our garden to make it more friendly to insects generally but particularly to butterflies and bees, introducing a wide range of flowering plants and shrubs to offer them as tasty a choice as possible.

    We are very rural, our house is close to one hundred and fifty years old, the brickwork on the south/south eastern facing walls are already providing overnight accommodation for lone bees

    We have recently been gifted a wooden bee hotel which was crafted by a bee enthusiast who has taken advice to ensure that it is as bee friendly as possible. We have noted from articles online as to where it should be positioned for the best results together with surrounding planting suggestions so we are now ready to go live!

    If you have any further information or particular advice, it would be very welcome.

    1. Claudia Garrido

      Yes, old houses are very popular with several bee species! They resemble vertical structures they would nest in under natural conditions. You might enjoy comparing who’s nesting in the house wall or the bee hotel. I guess there will be some differences. I may take up the subject again later this year.

  5. Hi, I recently made some bee hotels for friends and family (having read quite a lot around the subject) but unfortunately they did not get used, which was really disappointing! I wonder if you would be able to help me diagnose the cause, as I’d really like to adjust the design to make it more suitable.
    Best wishes and thanks in advance.

    1. Claudia Garrido

      Have a bit of patience. They don’t come immediately, it’s still early in the season (at least on the Northern Hemisphere). Without pictures or more info it’s difficult to give you indications.

  6. Hi. I’m in Lincolnshire UK. Last year a large swarm of Hone Bees descended on my small Insect hotel!! They completely filled all the holes within days. Now, May ’22, 3 types of bees are fighting it out? All the previous holes seem now empty? Honey bees, other 2, a small black bee and a brown and black bee? Not sure if I should leave it OR take it down? Suggestions please. TIA

    1. Claudia Garrido

      Definitely not honey bees, they don’t use insect hotels. A swarm may have taken it as a temporary stand before deciding where to go, but they definitely didn’t fill the holes. From your description it’s difficult to say anything. There are different species that use insect hotels, the most common ones are Red Mason bees, which could be the “brown and black”. They also fill the holes quite quickly, that’s totally normal. Small and black could also be a solitary wasp. No need to panic, just leave it alone. It’s normal that there’s some activity. There are excellent materials out there, try to contact a local conservation association to get more info.

  7. Peter Risebrow

    We have a bee hotel in the garden.
    For the last few weeks bees have been busy filling the tubes, and about a week ago they were all filled.
    Then yesterday we looked and every single tube except 2 are empty! My wife said this happened overnight.
    Do you have any idea what could have caused this please?

    1. Claudia Garrido

      OK, that’s unusual to that extent! The most probable reason are tits or other birds. For them, such a mass of nests is like an open fridge – an invitation to feed. This is why there are trap nests with a mesh in front of the holes. They keep the birds at distance. Sorry for your bee hotel!

  8. Richard Lawrence

    Hi, thanks for your article- I’m based in Somerset, uk, and am making a number of bee hotels for people to construct and take away from a community growing project I’m a part of. They will be made using bamboo sections, so a variety of entrance hole sizes. Aware this will only provide usable habitat for certain species- just wondered what your views on maintenance of these kind of hotels is? Many thanks, Rich

    1. Claudia Garrido

      Hi, thank you for your comment. Maintainance is a difficult thing in this context. People definitely have to know that the tubes closed in one year will hatch only the next one. I’ve seen people cleaning them out before hatching… sometimes the offspring also hatches only in the second year. So that’s the first thing: don’t “overmaintain”. There are people that take the cocoons out and overwinter them in a shed in the garden or something like that to reduce the parasitism. This is possible only in those trap nests you can easily open, with your bamboo sections this isn’t possible. One has to be aware, however, that a bee hotel is a massing of certain animals which obviously also attracts parasites. This is part of biodiversity, too.
      So, in your case, I’d just leave them alone, to be honest. If nothing hatches out of a stem for more than two years, you can change them out. If you see many small holes in the “plug” of the nest, that’s a sign that parasites hatched instead of the bees/wasps you wanted to attract. Then it may be time for changing out the stems and/or put them in a different place.

  9. Should bee boxes be out year around? I have just purchased one. Should I put it out now (mid Sept.) or wait till spring?

    1. Claudia Garrido

      Hi Elizabeth, sorry, I didn’t get a notification about your comment… Yes, you can leave them out all year round. During the winter, they also serve as overwintering shelter for other insects. In addition, they’re already there when the first solitary bees begin to search for a nest.

      1. Claudia Garrido

        Hi Violet, thank you for your question. You can buy them at garden centers and many places. But you’ll have to take care that they’re good quality. This means:
        – cleanly drilled holes (without splinters), so that the nest-building females don’t hurt themselves.
        – the holes should have diameters between 4-8 mm.
        – wooden disks look pretty, but they crack easily. It’s better if the wood is cut lengthwise, i.e. as the tree grows.
        You could contact a local conservations association if they have a good supplier, too. I don’t know all of them around the world, obviously.

    1. Claudia Garrido

      Not that much, fortunately. They regulate the number of cells according to the length of the tube. However, as the first cell is usually empty (measure against parasites) and the next cells are males, to have at least one female I’d say that the tubes should have at least 8 cm. The females maintain the population, that’s why males-only nests aren’t as “efficient”. Lots of biological background… will be maybe a subject for another post.

  10. Hello Claudia, I’m planning on making some bee hotels but I’m a bit concerned about siting as south facing is also the prevailing direction for wind/rain. Would it be advisable to have some sort of overhang to give protection or would the bees be OK without.

    1. Claudia Garrido

      The rain is actually a problem if it hits directly over longer periods. So yes, a small overhang of some sort would be better.

  11. Steve Browne

    I live in Munich, Germany.
    My homemade bee hotel is in its 2nd year and I have noticed that some holes are filled with mud/dirt and others with what looks like wax. What type of bee blocks in this way? Last year all the holes blocked were dirt coloured.

    1. Claudia Garrido

      Hi Steve,
      from the photos you sent via email I can’t tell, I’m afraid. What you call “dirt coloured” are nests of mason bees, with two species possible: the Red Mason Bee and the Horned Mason Bee. The waxy substance looks like resin to me, but bees using this to close their nests usually occupy smaller holes. I would go for solitary wasps in this case. They fill their nests with aphids, caterpillars etc., so are a great help in pest control in your garden!

  12. I have 2 bee houses that have much activity in the warm months here in Pennsylvania. However, I am moving soon in early December and want to know if they can be moved to a neighbor’s home 3 blocks away.

    Any help appreciated.

    1. Claudia Garrido

      There’s no problem in moving them when there’s no activity anymore. The adults you observed this summer now are dead, it’s their offspring developing in there. So, they don’t “know” where they are. Next year, they will hatch and orient themselves in the vicinity. If your neighbour has a garden with lots of flowers to feed them, I don’t see a problem at all.

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