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How to clean up from Nosema apis

Cleaning up after a Nosema apis outbreak is no easy chore. Your best course of action is to prevent an infection in the first place. My second piece of advice is to make sure it actually is Nosema apis that you are trying to clean up. It is easy to confuse simple honey bee dysentery with Nosema apis, so you will want a positive identification before you start. Identification requires a microscope and some training, or you can ship your sample to a lab.

Both Nosema apis and Nosema ceranae are transmitted by resistant spores that can survive long periods. The disease is transmitted when honey bees ingest the spores. This can happen when bees are cleaning the combs or other parts of the hive.

Since Nosema apis usually causes dysentery-like symptoms such as distended abdomens and defecation in the hive, it can be confused with normal wintertime honey bee dysentery which also causes distended abdomens and defecation in the hive. But with Nosema apis the spores pass through the digestive tract along with the feces. When other bees try to clean up the mess, they become infected as well.

Hive bodies, bottom boards, inner covers or any other wooden parts of the hive can be fumigated with various chemicals—such as glacial acetic acid—or they can be scorched with a blowtorch. It is best to first scrape all the wooden surfaces to get the thick stuff off, then scorch your woodenware and your hive tools with the torch.

A number of different chemicals can be used to fumigate combs, but none are very practical for the hobby beekeeper. They can also be irradiated or treated with ozone—also impractical and expensive if you have just a few hives. The simplest way to disinfect is with heat, but that isn’t easy either. Randy Oliver pieced together the following data that he found in a variety of research papers. The table shows time and temperature needed to disinfect Nosema-infected combs with heat.

Degrees F Degrees C Time
140 60 15 minutes
120 49 24 hours
104 40 5 days

Beeswax will melt at about 145°F (63°C), so if you decided to use high heat, you need a way to monitor and control it. As with your woodenware, I recommend that you first scrape the frames to get off as much residue as possible before you treat with heat.

All in all, prevention is far easier than trying to clean up. The best defense against Nosema or any other bee disease is to maintain populous healthy hives.

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    • Maintain large colonies going into winter. Combine small colonies with larger ones as long as they are all healthy.
    • Provide good ventilation so hives stay dry inside.
    • Ensure that colonies have adequate supplies of both honey and pollen going into winter.
    • Keep hives in a sunny winter location to encourage cleansing flights.
    • Treat for Varroa mites. Bees weakened by mites are more susceptible to a variety of diseases.
    • Continually replace old combs with new ones to prevent disease build-up.

If you believe your bees have Nosema or you want to prevent an infection from spreading, you can treat your colonies with fumagillin according to the package directions. Fumagillin is an antimicrobial agent isolated from the fungus Aspergillus fumigatus. The fungus is found naturally in soil and decaying organic matter. Fumagillin is sold under the brand name Fumidil-B or Fumagilin-B and is fed to honey bees in syrup. Fumagillin prevents the Nosema spores from reproducing in the honey bee gut, but it is unable to kill the spores.


Aspergillus fumigatus. Photo by CDC/Dr. Libero Ajello.

Aspergillus fumigatus. Photo by CDC/Dr. Libero Ajello.





  • So you do essentially discard any comb from an infected hive? I’d always thought that kind of drastic response was reserved for foulbrood.
    Tough decision.

    • Well, you can heat-treat the combs according to the chart. The problem is this: if you re-use combs without disinfecting them, you have to constantly treat with fumagillin. If you stop treating, the bees will come down with Nosema, usually in the first winter following the withdrawal of treatment. The spores can remain active for years. Some people do it like that and just keep treating and treating and treating. Is it really a tough decision?

  • How do you go about obtaining positive identification? Lacking a microscope and requisite training, is my best option to send in dead bees for analysis? If all the bees have been dead for a while, is there any hope of getting a positive determination?

    • Patrick,

      I would contact your local extension agent and ask where to take/send a sample. You need about 50 bees, if I recall, and they can be frozen. Like I said, the spores can last for years, so I don’t think the bees being dead for a while is a big problem, as long as they’re not decomposing.

  • Experience has shown me that once the main nectar flow comes on, these types of problems, dysentery especially, usually clear up quite quickly. Ozone has been recently shown to also clear up possible spore and bacterial contamination on equipment, including foundation.

  • Field test for nosema:

    Take a sample of about 30 bees. Take each bee & remove the head using tweezers to sever the mid-gut from the head. Grasp the last segment & sting with tweezers and, gently holding the thorax, slowly and firmly pull away. Place mid-gut on a white surface. If it appears tan coloured and wrinkly, it is healthy. If it is white & smooth, it probably has nosema.

  • Fumidil B is unfortunately no longer approved for sale in the UK, so we UK beekeepers now have to concentrate on good husbandry practices to protect against nosema.

  • On a related note, scientist Noah Wilson-Rich is planning to field-test an antifungal vaccine for honey bees this summer. The hope is that the vaccine will prevent Nosema.

    • Bob,

      There are documents available that tell you time vs. temperature and/or time vs. concentration. If you go by the charts you will be fine; you don’t need to test afterwards.

  • Where can I find a chart for the required rate of ozone flow (mg/hour) and time of treatment?
    Also, it would be good to be able to verify that the treatment was successful (dead spores) be for reintroducing the comb to bees.

  • Dipping wooden ware in paraffin wax seems to be promising, in theory.

    Add micro-crystaline wax or resin.

    It’s relatively cheap to set up, you can heat it to well over 300 degrees and it won’t damage the wood. (The wood can’t burn, since it’s submersed, so there’s no air for combustion.)

    About the only thing it won’t kill is AFB, which needs something like 375 degrees for 24 hours. This would be dangerous since you can’t leave the thing unattended.

    Most backyard setups are pretty much a larger version of a turkey fryer, with about the same level of risks in using them. You’d need a fire extinguisher, rated for grease fires, close at hand.

  • Questions: I was thinking about ways to heat sterilize frames, boxes etc to above 140 F for 15 mins without messing up my oven. Yes, that was an idea instead of a torch. [Boxes like a clay kiln idea.] But then just read dipping woodenware in paraffin wax heat it to well over 300 degrees and it won’t damage the wood. (The wood can’t burn, since it’s submersed, so there’s no air for combustion.) Like idea of dipping/soaking, but not paraffin
    [natural wax residue wouldn’t bother me].

    Here’s the questions > what if I used a metal small horse trough/tank set on blocks both ends and have a wood fire to heat just plain water. Then boil empty boxes etc for 15 mins or more. Do you think that would sterilize good enough? Would any tiny natural wax residue coating be safe since it was boiled too? I am trying to plan ahead for all > emergencies, medical, items, daily/monthly needs and well being of a hive of bees. before I take on the responsibility for their lives.

    I have to be creative on costs and way things can be creatively done, finding work-arounds for my disabilities and so my service dog can help me with. [Yes she will have a bee suit; I am designing so no stings on her nose or toes]
    I love your site it’s one of the best I can find.

    • Angel,

      Thank you for the compliment. But I have to say, I believe you are way over-thinking this. I wouldn’t worry about sterilizing bee boxes unless you actually have to do it. In all my years of beekeeping, I have never had to sterilize a box and never had a Nosema outbreak. If I have one in the future, I will examine the condition of the equipment before deciding what to do. The contingency you have to face probably will not be one you anticipate, and the possibilities of things going wrong are endless.

      If you want to study in advance of getting your bees, study bee biology and the life cycle of Varroa mites. Nothing will help you more.

      But anyway, if I had to sterilize a box today, I would use a torch.

  • Thank you for your very valued opinion on torch. Yep, studying bees and the cycle of Varroa mites. Weekly powder sugar poofed into hive entrances not brushed, sprinkled top of frames. Less annoying to bees. Do when the pollen/nectar gathering workforce bees home early morn or best choice evening after their mingling with stranger bees out in the world. Cuts that extra 12 hr Varroa mites sleep over. Doing less than weekly increases potential infestation time but tri-weekly it’s not really worth it. Drone frames rotate replace between 14 to 21 days. Feed hose-blasted drones to chickens as treat. Will have anti-chicken fence around hive area. Don’t want bee drone addicts pestering hives when it’s their backyard playtime. Henny Penny is very observant chicken. Does that seem a good plan?

    Yes, I over think everything in life thinking possibilities/probabilities and potential contingency plan options. It’s my curse or strange talent to collect helpful and odd interesting info. What’s weirdly amazing is some of the pre-thought out options to real strange circumstances that in your wildest dreams you don’t think you will ever have happen. Years later something similar happens or I receive a call from friend or neighbor with a crisis. True no one can plan for all possibilities but I guess I enjoy running scenarios in my head.

  • Thanks, Rusty! Most concise, on point info I’ve found to address sterilizing suspected Nosema infected woodenware. I’ll be sending samples to Beltsville to be certain before I go to all this work but at least I feel confident of a way forward. Big relief! Thanks again.

  • Rusty,
    First year beekeeper here. Your site has become my favorite as I begin my apiary journey.

    I have one hive that by my novice eye looks solid and strong going into winter here in Maine. My concern is Nosema. Not that I suspect my girls are infected, but that we were told in our class to treat for it going into winter as a preventative. After some research, I am not sure that is the right course of action. Can you offer some guidance, please?

    Thank you!

    • Brenda,

      Nosema is complex. It used to be that Nosema apis was the problem and it could be prevented by fall treatment. But now in lots of areas, Nosema cerenae is displacing Nosema apis. Unlike N. apis, N. ceranae is a summer problem, rather than a winter problem. So it seems, at least in some areas, that winter treatment for N. apis isn’t really necessary anymore. Also, some beekeepers feel that the drug used, Fumigilin, kills many of the “good” microsporidians that live in the honey bee gut as well as the bad ones.

      Personally, I don’t treat proactively for Nosema, although if I had an outbreak, I probably would. If nearby beekeepers are having trouble with it, you may want to treat. But otherwise, I don’t think it’s necessary.

  • I am in Nova Scotia, Canada. I’ve lost 3 of my hives to what seems to be Nosema. Since I am trying to treat organically, I am wondering if it would be possible to fog with mineral oil and a few drops of tee tree oil? Would this be an effective treatment for nosema without harming my bees?

    • Debbie,

      I doubt it would be an effective treatment. If it were that easy to handle, we wouldn’t be having such a big problem with this disease. My first piece of advance would be to have your bees tested, rather than just guessing. At least then you will know for sure what the problem is (or isn’t).

  • I got lab reports from Beltsville last week telling me that my 10 hive loss (my entire apiary) was due to Nosema c. My bees all died within 2 days in mid December. I had no sign of trouble. And I didn’t have nosema on my radar for preventative treatments.

    So, each hive had 8 frames of honey and 2 boxes of drawn comb. I extracted honey from one box but haven’t yet bottled it. I can eat the honey, right? I don’t want to let new bees have it.

    The Dr Webster article mentioned last year (in this forum) isn’t available any longer. I don’t know what he was suggesting as a solar option, but it sounds like I can put all the frames in the oven at 140 degrees for 15 mins and reuse them. I do have a greenhouse that gets up to 120 during the day but it gets chilly at night. I’m hesitant to just put them there – but it surely sounds like less of a fire hazard. Thoughts?
    I’ll scorch the woodenware.

    This is a devastating loss for me. I’m only in my 3rd year keeping bees. I have used Apivar for mites but I am planning on switching to oxalic acid this year. The Beltsville report cites a high mite count so Apivar isn’t my friend anymore.

    If someone has been through this please correct me/set me straight. I have bees coming in April and I want to be ready.


    • Donna,

      Humans can eat the honey with no issue. For disinfection, read Randy Oliver’s article regarding disinfection of nosema hives. In part he says, “Most spores on beeswax died within a few weeks at broodnest temperature or if frozen; but at room temperature some survived for up to a year. Surprisingly, although freezing quickly kills spores on beeswax, it helps them to survive longer if they are immersed in honey, in which they can survive frozen for well over a year. If the honey, on the other hand is kept at broodnest temperature, the spores only remain infective for several months. So either freeze your contaminated combs or keep them warm, but don’t feed back honey that’s been stored frozen.

      “Combs without honey can also be decontaminated by fumigation with acetic acid. The spores are also easily killed with bleach, but I don’t have hard data on the best application method.

      “In our operation, we routinely reuse the boxes of combs from deadouts without performing any disinfection whatsoever (other than to check for AFB). But we typically reuse those combs later in the springtime when colonies are able to purge the parasite.”

    • Donna, Sorry for your loss too! Here in NW Iowa.
      I had 17 HEALTHY COLONIES at the start of August 2019. – Now 100% loss on all our bees too !

      I had 4 hives collapse starting last fall 3-4 weeks after farm pesticide was sprayed on corn & bean fields with airplanes. Our bees lost huge amounts of forage bees and were weakened substantially. Shortly before that a migratory bee keeper had dropped 30+ colonies 3/4 miles from us. Their bees were dropped without honey supers. Dearth was on and their bees found ours and attacked in a robbing frenzy. We had robber screens on but they were still fighting and killing each other at front of all hives. We know the robbers were getting in because of honey wax cappings dropped on bottom boards.
      – – –
      I took samples of dead bees from 4 hives + one random collection from 12 hives, and SENT with Iowa State Apiarist mid October for inspection.

      REPORT ON my bee sample INSPECTION by State Apiarist – December 12th, 2020

      “State Apiarist checked each sample for a Nosema count- a fungal gut parasite which has flared in some operations in recent years. I think we found your culprit, or at least a large contributing factor to the losses.”

      “A common threshold for deciding treatment is at the 1 million spores per bee level. Our spore count was well above that million for 4 of 5 hives tested. Apiarist said the treatment is Fumagillan. Its not a perfect cure, it’s expensive, it can be hard on the bees in and of itself, and you wouldn’t want the residues remaining to contaminate your surplus honey … so I don’t advocate Fum treatment unless it’s found to be necessary.
      I believe water sources can be a common source of contamination outside of the hive.
      Inside a hive, the infection spreads fecal-oral as nurse age bees struggle to clean up after the sick bees. Once the Nosema has made its way to the bee’s gut, it multiplies, and the infection snowballs further. Fecal contamination on combs is an issue. So be careful in handling / swapping combs from hive to hive / and installing new bees onto contaminated combs. UV in sunlight is at least somewhat effective in killing spores, so consider “sunning’ the combs from any deadouts come spring for a couple days each side, especially if there are signs of dysentery.”

      How about cleaning up Frames and Comb in the spring?

      State Apiarist response.
      “ I would just scrape any fecal residue down and sun them. I’ve heard of vinegar spray and bleach spray. It may work some as well. There’s an actually effective strong acetic acid fume treatment, but it involves high strength acetic, not regular vinegar, and temperature controlled heating. The dysentery is more a symptom of stressed dwindling bees. Not really associated / correlated with Nosema itself – though you’ll see this notion shared widely. People see the bee crap on the top bars or around the exit and immediately think “Nosema” … just not the case. It may have been something of a stronger assumption a while back when all we really dealt with was N apis. But with N ceranae, there’s just no real association. I don’t have the ability to determine which species of spores I see when doing the counts. ”

      I didn’t see much of the fecal matter in our hives.

      I knew our bees were in deep trouble Mid September when we lost our FIRST colony quickly.
      We inspected all colonies and every queen had stopped laying eggs mid September.
      Not much capped brood left, so back that up 21+ days is getting near the time crops were sprayed with pesticides.

      It was mid December when we received our bee inspection report, so it was winter and too cold to do anything.

      MY SUSPICION on the complete loss of our bees. Lost our last hive February 12th.
      What caused our queen bees to stop laying all at the same time?

      #1 • Large loss of forage bees in all hives dying from pesticides spray drift and/or neonictinoids in crop pollen brought back to hives. This quickly made our bee colonies sick and weak. We had two days we could smell strong pesticide spray in the air in our yard. The spray airplane hit us bad.

      2 • Hungry migrant bees robbing ours. Did they spread the nosema disease? I believe so.
      Why do I believe this? After 4 colonies of our bees died. I did a quick inspect, looked in 10 of the 32 migrant bee hive colonies. 7 of the 10 were dead empty. Thats 70% loss before middle of October.

      3 • Deadly combination. Our bees became sick from the poison. Queen bees stopped laying. Migrant bees spread the disease. Our Nurse bees trying to clean up all the sickness became overwhelmed by nosema.
      Not any new winter bees born late in the fall to survive the winter. Bees just kept dwindling to nothing.
      Each of the hives ended with less than a fist size bee cluster with queens found in center in all but 2.

      SAD to say we have to start over.

      I am going to clean out dead bees, scrape frames etc. THEN, do the acidic acid fumigation treatment in sealed boxes and frames for a week. After fumigation, I will “sun” the frames for two days each side for extra precaution.
      Lots of brood box honey left since the bee numbers dwindled so quickly.

      All before new bees come in April. (4 pkgs to build from again)

  • Hi! Many of my dead bees have there tongues sticking out is this a sign of nosema? A lot of people are saying poison or something else, but it’s winter so I don’t think it’s poison. I only started last spring so I’m very new at this?

    • Daniel,

      Tongues hanging out are associated with poison. I don’t know if there’s a connection between tongues and Nosema.

  • Hi! I’m back. I have spent a month cleaning 10 hives that had verified Nosema. I used a propane torch on all the woodenware. I’m ready to assemble and do acetic acid fumigation. Has anyone here done this?

    I have new equipment that I am going to use with oxalic acid for mites. I was hoping I could use a similar process with acetic acid. But what strength acetic acid? The internet has way too many tips on this.

    And I have one more question about the brood box honey, please. I have a ton of this honey for the bees coming next month. I did not freeze it because I read that freezing is a friend of nosema. Sunning honey does not seem effective. But I don’t want to go through all this cleaning, scraping, and scorching only to feed nosema to my new bees. What is the best way to treat the honey?

    Many thanks for your help!

  • How about boiling frames to clean off spores and such, especially when you have wooden frames and plastic foundation. I’ve seen that on YouTube. Any thoughts?

    • Honestly, I don’t know if boiling kills nosema spores. I know there are many spores that are unaffected by boiling, such as botulism.

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