Honey Bee Sauna: “Keeps Bees from Roaring”

Mites on brood

Varroa mites on brood

Varroa, the destroyer

 A German “crowd sourcing” fund wanted 10,000 Euros to build honey bee saunas. Within a few weeks, they had over 60,000 Euros in pledges – that’s about $75,000. I guess that the contributors don’t realize bees can die in a sauna. Back to that in a minute.

Varroa, hitching a ride and sucking blood

Varroa mites kill bees. To eat, the nasty mite-creatures grab hold of bees and suck up their insides. Eventually, all colonies with booming varroa mite infestations die. That’s why beekeepers try to poison varroa mites – usually treating their bees with pesticides. Pesticides can leave trace chemicals inside the hive and become dangerous to bees and bee handlers. Further, the mites may evolve resistance against the poisons. Unfortunately, various chemical treatments seem to be the only currently effective and widespread weapon against the deadly varroa mites. But other methods are being tested.

Just as mites evolve to resist chemicals, honey bees may evolve to resist mites. This is the idea behind the celebrated Russian bee. Honey bees found in eastern Russia seemed to have evolved to live with mites. The claim is that most untreated honey bees will die, but a small subset will have some genetic quirk that will allow them to survive varroa attacks.

Genetically quirked bees will reproduce and repopulate the ecological niche lost by their vanquished sisters. This may have happened in isolated areas, such as Siberia. Unfortunately, when the Russian bee was brought to North America, its genetic advantage was quickly diluted by other honey bees already extant in the hives of commercial beekeepers. You see, queen and drone bees fly many kilometres to clandestine rendezvous hangouts where they indiscriminately mate. This evolved habit prevents honey bees from becoming inbred and fosters genetic diversity – within the same colony any two randomly selected co-working workers are likely to be half-sisters, not full sisters. Although this diversity gives many advantages to a colony, it almost kills the idea of maintaining pure-bred naturally mated lines of pest-resistant bees. It takes a good queen breeding program to maintain stock that keeps a line of honey bees imbued with hygienic behaviours and other qualities that suppress varroa populations. There are such queen breeders around and it can be done – but without discipline and diligence, varroa will creep back into an operation.

So, if chemical treatments eventually fail and genetic solutions are hard to maintain, what might be done to fight the dreaded varroa mites? Some beekeepers have lured mites to drone brood, then discarded the comb; others have reported some success dusting powdered (icing) sugar on bees to extricate mites. Greasy vegetable oil sprayed on the bees may slow down mite infestations. A completely different idea – heat – has been occasionally promoted and seems to be going through a bit of a popularity renaissance. Varroa mites, it seems, can’t cling to honey bees if the temperature is hot. This has led to a number of schemes that warm the inside of a hive (or a cage of bees) until the mites fall off. Unfortunately, this does not kill the varroa mites, it just dislodges them – chances of success are likely pretty sketchy using this system.

The USDA studied this idea 15 years ago. You can read their report at this link. Here’s the problem: at temperatures of 40ºC (104ºF) and higher, mites slowly fall off honey bees but bees begin to suffer heat stress. Honey bees, as you likely know, try to keep their nest temperature at about 35ºC (95ºF). Way back in 1791, Francis Huber discovered that even on the hottest summer days, bees did not allow their nest to rise above 99ºF. Remember, mites fall off at 104ºF. So it is hard to get a high enough temperature inside a hive to dislodge varroa mites. The bees will fan and evaporate water and reduce the hive temperature so they do not die of heat exhaustion and so their wax home doesn’t melt into a candle-like blob. High air temperatures dislodge mites if the temperature is warm enough for a long enough period of time. Higher temperatures (over 45ºC or 113ºF) will make the mites fall in just a few minutes, but will also kill honey bees more quickly. The USDA study shows that bees get crispy if they are exposed to too much heat – or even a little heat for too long a time. Quoting the USDA 2001 study: Overall, heat treatment is a risky procedure. Even 40ºC, the lowest temperature that can remove all the mites is perilously close to temperatures that kill bees.”

With these potential problems in mind, I was surprised to see that a German Crowd Sourcing Fund was able to quickly raise a huge amount of money to build a Bee Hive Sauna. The crowd sourcing goal was 10,000 Euros. They have over 60,000 Euros in pledges – that’s about $75,000. Their self-promotion site includes the non-Einstein quote (“…if all the bees die, in 4 years you will too…”) and it includes lots of Wir retten Bienen (“We save Bees”) subtexts. So, the promoters know how to appeal to the heart-strings of the misinformed. My guess is that the contributors/donators/funders don’t realize that bees can die in a sauna. The trick that keeps the bees alive, according to the inventor, is that (with his Bienen Sauna) “The Bees do not roar.” (OK, maybe it’s the Google Translator. The original German is Die Bienen brausen nicht.) I have never heard of roaring bees, but roaring seems like a problem to be solved. I will probably get the story wrong, so let’s allow the inventor, Engineer Richard Rossa, to explain:

“The bees do not roar.” “In my trials I came to the realization that roar of bees is not caused by a slow heating of the ambient temperature, but by increased CO2 content of the air. However, this effect does not occur in the treatment with the bees sauna. If necessary, fresh air is supplied at any time. This is done controlled so that no draft is produced. “Holding the air temperature constant between 40°C and 42°C, all Varroa mites, which are long enough exposed to this temperature, irreversibly damaged. Should any of Varroa mites survive, they are so damaged that they can no longer reproduce. Broodless colonies are treated for 45 to 60 minutes. Those with brood take two hours because it takes longer to warm through the brood cells. Then the device switches off automatically. In the entire time temperature and humidity are constantly monitored and regulated in the hive.”

It appears that by ridding CO2 from the hive, the bees won’t roar. If you read their website, you will see that (for about $1,000 per unit) it will be just the varroa mites that do the roaring. Rossa says that the temperature inside the hive/sauna will be kept at 40 to 42ºC. As we have already seen, this is a good bit warmer than the bees like, so I suspect some energy will be wasted by the bees as they gather water and circulate air to get the hive temperature down to their preferred 35ºC. Or I could be wrong. It could be that I am just an old-fashioned cynic who is spouting off about any product that has been tried in a number of commercially available guises over the past few years (see the Mite Zapper and the Varroa Controller).

Maybe I am cynical because some gullible people will quickly fund any cool yuppish idea – even if the procedure has been shown problematic by USDA researchers. However, I do not have a PhD in “Co-operative Communication Strategies for Politics and Media”, whereas Richard Rossa’s partner, Dr Florian Deising does. He was “a management consultant, financial manager [who] led international projects in large corporations… [But 2 years ago, he] got out to make as it were full time our world a better place”. I suppose these guys have their heart in the right place and they obviously know how to work a crowd for money. And perhaps they know how to keep bees from roaring in the sauna. It would be great if some sort of well-engineered hot-hive can actually kill varroa mites without hurting bees. That would eliminate chemical treatments. But at almost $1,000 for each device, the Bee Sauna will probably meet limited success. Personally, I think the long-term future for varroa control will be in genetic manipulation, not in heat. But check out the Bee Sauna at wir-retten-bienen.org (“WE SAVE BEES.ORG”) for yourself and make your own informed decision.

Richard Rossa, inventor of the Bee Sauna

About Ron Miksha

Ron Miksha is a bee ecologist working at the University of Calgary. He is also a geophysicist and does a bit of science writing and blogging. Ron has worked as a radio broadcaster, a beekeeper, and Earth scientist. (Ask him about seismic waves.) He's based in Calgary, Alberta, Canada.
This entry was posted in Bee Biology, Diseases and Pests, Genetics, Tools and Gadgets and tagged , , , , , . Bookmark the permalink.

17 Responses to Honey Bee Sauna: “Keeps Bees from Roaring”

  1. Bärentatze says:

    “As we have already seen, this is a good bit warmer than the bees like, so I suspect some energy will be wasted by the bees as they gather water and circulate air to get the hive temperature down to their preferred 35ºC. Or I could be wrong.”

    Yes, you are wrong. Bees start to ventilate cold air into the hive, when there is cold air available. As there is no hole in the hive during the treatment, there is no ventilation by the bees. Water is provided too keep the relative humidity at a good level.


    • Miksha says:

      If I am wrong, this contraption is worse than I indicated. You are saying that there is “no hole in the hive during treatment” – so the bees simply overheat! I am surprised that this product is allowed to be sold – and for such a huge price! (The “sauna” with battery is $1,700 US, plus shipping!) According to the USDA report on heat treatment for varroa, this is a dangerous and ineffective way to treat for mites. Overheating bees, even if it is for a brief period and even if does not immediately kill them, significantly shortens life expectancy. However, these similar heat-treatment devices keep entering the market every few years.
      I see that this equipment is heavily funded by the Bavarian government, using the “Save the Bees” mantra. Regardless the German funding, the manufacturer even sent a letter to Barack Obama asking for one million Euros: “Letter to Barack Obama: Euro One Million for the Bees Sauna”. Are you sure this is not simply some promotion-gimmick company, rather than a real effort to “Save the Bees”?
      Here’s the problem: If the bees don’t die, the mites are not killed in sufficient numbers. If the mites die in sufficient numbers, the bees are severely stressed – or they die. For nearly $2,000, perhaps the machine can keep the bees alive and kill the mites, but I would need to see independent tests furnishing proof before I would believe it.


      • Bärentatze says:

        You say, “the bees overheat”. Literally, that is what hyperthermia means. Yes, they are overheatet. But your conclusion is wrong.
        Bees can stand 42°C, even more, 45°C. Mites can not stand 42°C, because a certain protein in them collapses over 40°C.
        I own a Bee Sauna and my colonies are more vital after the treatment than before. An increased number of mites falls over the next week. It works, the colonies have been treated several times. Come and visit me, see it yourself 🙂
        You can see through the transparent cover that the bees are calm during the procedure, because they are heated very slowly.
        (Actually, I think that some other hyperthermia machines have a rotating box so you can not see that the bees are upset… I guess, they get upset because of the rotating on its own.)
        No bees die during the treatment (in 6 treatments there was one dead bee on the bottom).
        My colonies have not been treated with chemicals since and the number of varroa mites is about the same as with chemicals.
        Currently the wellknown German bee scientiest Gerhard Liebig (http://www.immelieb.de/) is doing a long term testing (a long therm testing, so to say:-) ).
        By the way, I am not payed by the bee sauna producer or anybody else for this comment.


      • Miksha says:

        Hello, Bärentatze;
        First, thank you for following our blog – that’s very nice of you! I see that you are associated with the bee sauna and you support the effort to use heat to kill mites. Does the gadget actually cost $2,000 Canadian to treat just one hive? Hopefully, you can make the price cheaper in the future.
        All the evidence continues to point to the harmful effects that heat has on bees. You might not see many dead bees in the hive, but with shorter lifespans, they die earlier during foraging. Of course, anyone who has handled and hauled thousands of packages (as we have done) knows how easy it is to lose bees through overheating and how risky heat exhaustion is. Calling the machine a sauna and indicating that the bees are roaring (a sign of stress) indicates the risk involved in heating bees to kill mites. But in your own experience, it works. At $2,000 per hive, I hope so.
        I went to Professor Liebig’s blog (you kindly provided the link) but could not find any information about the hive sauna, except for a brief (6 words!). Can you please give us all his information on the experiments he is conducting?.
        Thank you for the invitation to see your sauna in action in Germany. It would be wonderful if it works – and if the price were about $50 per hive instead of $2,000! 🙂
        Ron Miksha


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  4. Bärentatze says:

    Hello Ron,

    yes, one “Bienensauna” costs1350 EUR, and I assume you calculated correctly for the Canadian Dollars.
    But you can use one Sauna to treat several hives one after another, which is no problem for beekeeping hobbyists. It might be a problem if you have hundereds of hives. Than would take a small powerplant to treat them all at the same time.
    The team is a small kickstarter company, and as they are doing small numbers, the prices are still high. I hope that the Sauna will be cheaper, soon.

    I have no means to figure out, if my bees die earlier when treated with heat.
    But I have no means to figure out, if my bees die earlier with chemicals either.
    With heat I only treat one generation, but the chemical rests stay in the hive.
    Therefore I like the heat better.

    Again, there is no roaring. The Sauna keeps control of heat and humidity. I will make a youtube video to show how relaxed the bees are during the treatment, filming an independent thermometer.

    Here is the subpage with Liebig’s experiment:
    http://www.immelieb.de/?p=1601 (Use google translate or similar).
    He is the operator of http://www.hobos.de (which is multilingual). You can read about his experiments in general here. At least one of the hives is always “online” with weight, temperatures, humidity and weather measuring.

    Actually, the Bienensauna homepage promises quite a lot.
    I am not sure, if all that is easy to prove, you would need several colonies and control group colonies…
    I would be happy, if even only the varroa reduction works fine. And that is my experience so far 🙂
    I don’t care about honey production and whatever, as long as it is not worse than with chemicals.



    • HI there.
      I read most of what you both were discussing and I am now really suspicious about the Sauna and overheating process. A Simple search for the keyword “sauna” reveals that there are several critical articles about the product. Not effective for a lot of money seems to be the conclusion. http://www.immelieb.de/?s=sauna
      CIAO . Stefan


      • Ron Miksha says:

        Thanks, Stefan, for your comment. Unfortunately, the ‘sauna’ does not work. Worse – according to researcher Dr Gerhard Liebig, queens were actually killed in the process of testing this particular device. Years ago, the USDA did a series of tests on heat as a method to kill varroa, but they found that the heat needed to kill mites seriously stresses bees. There is a small window after which the bees drop dead. Even below that, bees suffer – as Dr Liebig showed.

        Liked by 1 person

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  7. So what else can a concerned beekeeper do than to use Drone frames 2x a year to keep the mite population at bay? I am quite insistent NOT to introduce chemicals into my hives, just like I don’t let pharmaceuticals into my own body if not absolutely necessary. There is always another way. But I have to say, my other way for mite treatment cost me a loss of 14 of my 15 colonies last winter. By far the worst in 10 years of keeping bees.


    • Ron Miksha says:

      Sorry to hear about the huge loss. Unfortunately, without treatments, varroa kills colonies. Natural treatments vary in their ‘naturalness’ and in their efficacy.

      Among the relatively effective ‘natural’ treatments are formic acid (which occurs in honey) and oxalic acid. Other treatments often work, or at least help somewhat: icing/powdered sugar dustings, screened bottom boards, hops treatments (HopGuard), small-celled brood combs, vegetable oil (often combined with wintergreen), Thymovar (thyme oil ), queen arrest methods, and freezing drone brood. I guess there are others, too. Some of these barely make a dent in mites some years but work (somewhat) other seasons. Probably an integrated approach would help.


      • Thanks Ron. I will have to seriously look into a form of treatment that I can do to prevent a loss like this to occur again. It is not good beekeeping either if you don’t take care of your “girls” and let them suffer and eventually die.
        Just don’t want to send them through a “Chemo Therapy” where they walk away from so weak they might suffer the similar or same fate than without. Let the treatment yield better and stronger bees, not weaker ones without mites.


  8. rob says:

    1) The USDA findings are based on tracheal mites not destructor…big difference and no valid assumptions can be made based on that study.IMHO
    2) The natural defense mechanism for honey bees is “balling” by generating their own heat over 42C; so what is more natural than helping them destroy pests naturally.
    3) Paying for equipment that can be used over and over on multiple hives with a simple cost for energy is FAR, FAR, better than paying thousands upon thousands for treatments putting poison into the hive with poor results at best.
    4) the mites don’t get hot and loose their grip…that is plainly not the discovery at work here. They undergo a metabolic change that causes terminal damage and they do die within three days when exposed to temps over 42C.


    • Ron Miksha says:

      Wow, Rob! Thanks for writing.
      First off, please take another look at the USDA paper which we linked in the blog. The name of the USDA paper is “Heating Adult Honey Bees to Remove Varroa Jacobsoni.” It is not about tracheal mites, which of course is quite a different animal. You might find the varroa article from the USDA interesting.
      Secondly, you write “the natural defense mechanism for honey bees is balling.” Actually, the natural defense mechanism for honey bees is the stinger. Balling occurs when the bees are killing an unwanted virgin or an intruder such as a wasp. They don’t use it to kill mites. Bees rarely use balling because it causes considerable stress on the bees and kills some of them in the heat ball – similar to what the USDA warns about.
      Third, I agree! If something can be used cheaply and easily to kill mites, that would be great. But paying for something that the USDA says doesn’t work is a waste of money – and it can kill bees. You might like to read this 2016 test of heating to kill varroa – the heat not only failed to kill mites but instead killed two queen bees in a test of 16 colonies. The complete results, control hives, and testing procedure conducted in Professor Liebig’s experiments and his piece “Viel Aufwand und keine positiven Effekte” is here: http://www.immelieb.de/?page_id=1668.
      Finally, just curious, but what do you mean the mites “undergo a metabolic change that causes terminal damage” but you say the mites don’t get hot. What does that mean?
      Hope spring comes soon down in Carolina and your bees get off to a good start! Good luck with the season.


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