bee feces

Nosema and dysentery are not the same

Yesterday I read the following statement on the blog of a well-known beekeeper. “First I looked at the hive entrances which had signs of nosema the last time I visited. The hive looked just the same – no new nosema on the side of the hive.”

Whoa! There are at least two things wrong with this statement. First off, you cannot see Nosema on the side of a hive. What you can see on the side of a hive is bee feces, which may or may not contain Nosema. More often than not, an accumulation of runny brown feces at the entrance to a hive in spring is honey bee dysentery. Unlike human dysentery, honey bee dysentery is not caused by a pathogen but by poor diet.

Not all Nosema is the same, either

It is true that Nosema apis also causes diarrhea-like feces to be deposited in or on the hive, but it cannot be distinguished from dysentery without a laboratory analysis—or at least a microscope and some training.

Secondly, Nosema ceranae, which also can infect honey bees, does not cause the bees to defecate in or on the hive. Most often bees become infected with Nosema ceranae in the summer and die in the field while out foraging. In any case, bees infected with Nosema ceranae do not leave diarrhea-like feces as a clue.

In summary, seeing no feces does not mean the bees are free of Nosema anymore than seeing feces means they are.

Honey Bee Suite


  • I wonder if Fumagilin has any affect on Nosema ceranae? I haven’t found anything with a solid, conclusive, yes or no, yet. Some say yes. Some say no. Some say a little and I still don’t know. Are there any scientific papers on this? I can’t seem to find them if there are.
    They say the bees will overcome Nosema A, if you let them deal with it. They need to have it, to beat it, without treatment. They can’t beat Nosema C, from what I understand. If Fumagilin treats Nosema C, even a little, then treating is a must.
    I guess I’m just not that daring yet. If I caught a serious bug, that could kill me, I would drink my Fumagilin.

    • The things I’ve read about Nosema are just as you say. The bees can beat N. apis but not N. ceranae by themselves. Some say Fumagilin-B works for N. ceranae and some say it works partially or not at all. Some say it requires larger doses, but no one has said (as far as I know) what those larger doses are. I don’t know anymore about this than you do.

  • Does regular bee dysentery in the spring need to be treated or will the bees overcome it on their own as temperatures warm and they are able to spend more time out of the hive? I do try to clean up what I can to get the feces out of the hive.

    • Darwin,

      Yes, usually honey bee dysentery clears up by itself once the bees start flying and have a spring diet. I do the same thing—clean up the best I can and call it good.

  • Thanks for confirming the possible confusion. I am a first timer, and I wasn’t sure what to think when after the first couple days of sun, the front of my hive was covered. We haven’t had great weather to open the hive up and really inspect. Sounds like I am ok to assume spring dysentery…unless the dysentery doesn’t seem to improve?

    • Jenn,

      It can be confusing, but if it clears up quickly, it was probably dysentery. Also feces that is brown and runny should quickly change to yellow globs that sort of hold their shape. Nosema apis can sometimes clear up on its own as well, but not as quickly and sometimes with significant bee loss.

  • I am a first year beek. I have my first over-wintered hives. I had two colonies. One colony turned out to have massive streaking and tons of dead bees. The hive right next to it was completely clean. This summer my clean hive is busy, lots of pollen coming in on sunny days. In North Central Idaho we’ve just began to have days that are warm enough to crack open the hives. My “streaked” hive had a few bees coming and going, all without pollen. I suspect they are neighboring bees robbing the stores of the slow (or dead) hive. I opened up my slow dirty hive, and no bees were there. They died, ug. I feel terrible. Can they die from dysentery? We’ve had such a long cold winter. They still had plenty of honey stores. Can I eat that honey? Can I feed it to my good hive?

    • Bridgett,

      Bees can die of dysentery but I suspect yours had Nosema apis. I wouldn’t feed the honey to new bees unless you first had the dead bees tested for Nosema. If they didn’t have Nosema, then it’s fine for feed. You can eat it in any case because humans don’t get Nosema. However, before you extract it, make sure you clean the feces from the combs. I would use a wash of bleach water, gently applied to the combs and then allowed to dry.

      As for cleaning up the equipment, this may help: How to clean up after Nosema apis.

  • Thank you so much, I will go forward as if Nosema is present. Also, do you know of a colleague, someone who knows honeybees at University of Idaho? If not, I can call the entomologist there. I am a Vandal too. Thanks again Rusty.

  • Okay I have a question about this. I have my first northern hive, back home after many years. The weather this winter has been rough, high winds, really cold we reached -53 C with the wind chill this winter and had -40`s C for a good two weeks… obviously the bees were not out… it`s now mid February and they are making their first cleansing flight of the winter. They have tossed thousands of bees..and I`ve pulled as many off the bottom board via the bottom entrance with a thin needle… to me… given that there was 60,000 or more bees going into winter 10 to 20,000 dead appears to be a reasonable amount… there are regular dead on the porch every two days or so that I clear as well. I can hear them humming..all signs that say it`s a healthy hive. So today being 7C I opened the top and lifted my interior bee dry pillow to find the cluster right there… I had wanted to check the honey stores (I left two deeps and a medium super of honey for winter stores). Close it back up again right away after seeing the cluster. But I did notice dysentery. Some dark brown mostly yellow. Now I`m assuming this is from the long winter and harsh cold weather keeping them inside… I see nothing to indicate Nosema is the problem. Given the color changes I suspect it is also being taken care of… and I can see bees literally being thrown out the top entrance….. am I correct in my assumption that all is well…

  • Hi Rusty,

    I looked for a discussion to this question but I couldn’t find one on your site, so here it goes. This is the first summer that I am beekeeping. When I first received my nuc in mid-June, I gave the bees a Nosema treatment with fumigillan. I treated for mites in July, late Aug and Oct. I am really upset with myself for forgetting to give my bees a Nosema treatment prior to winter. I live about 30 mintues north of Boston and the weather has been very erratic now that we are in the first week of Nov. It seems that feeding sugar syrup is done for now as there have been nights below 50 degrees. We’ll have 3-4 warm days with night temps below 50 and now were having some days at 60 degrees with night temps at high 40’s. My question is: Now that I can’t use sugar water as the agent for the Nosema medication, what can I do now? Is it possible to mix the formula in with fondant? Or do you know of another way? I’m very worried about if they can make it through the winter without getting this. I did feed them with Honey b-healthy mid-Oct in 2:1 sugar water. Will that treatment help prevent Nosema? Any help is appreciated.


    • Alicia,

      I don’t know many people who still treat prophylactically for Nosema except some of the commercial beekeepers. Fumigillan is nasty stuff, so why use it if you don’t have to? In any case, it is no longer available. The company that made it went out of business and I don’t know of a replacement. Anyway, to answer your question, I believe that syrup was the only effective way to give it to bees. It wasn’t recommended to give it dry.

  • Hi Rusty,

    Coming from a recent postmortem, I’m tackling the nosema v. dysentery v. other causes issue. The hive wasn’t as strong as I would have liked going into the winter, however, our winter set-up was a double deep with a no-cook candy board (10 lbs sugar), upper entrance shim, and quilt box. The bees were visited weekly or every other day throughout the winter just to listen at the side and check for signs of melting snow at the entrance. They appeared to stay in the lower box for most of the winter (assumedly relying on honey stores). But come February the hive was silent and dead.

    I’ve never dealt with dysentery or Nosema before, but my first investigation seems to be pointing in that general direction, as one of the first things I noticed at the hive were the tell-tale dark stains from feces on the front of the hive. Upon opening it up, the cluster was quite small and right up near the sugar which they had only just started working on.

    My initial response is that the colony started off too small in the fall, and was potentially further weakened by disease until the colony was too small to keep itself warm. We’ve had 7-10 days of -25 to -30 degrees Fahrenheit, so there’s been no opportunity for cleansing flights either.

    Additionally, I did reach out to our local University Extension to ask if they or anyone they were aware of offered Nosema lab testing, and they responded that they do not and that they do not recommend sterilizing the equipment even if the colony death was related to Nosema. This is contrary to what I had understood? I had been under the understanding that the spores could persist for years and that not sterilizing the equipment in some way will just lead to the same issue every year?

    What are your thoughts on sterilizing equipment without any way to get a positive Nosema ID “just in case”? (I did also try the pulling the heads off field test method, but don’t want to take that as any certainty).

    • Stephanie,

      My first question is whether you found feces inside the hive. Feces outside the hive could be from cleansing flights but finding it inside the hive is often associated with nosema. That’s not a hard-and-fast rule, just an observation.

      I’m surprised that your extension people do not recommend sterilization after nosema infection. Lots of places do recommend it. The reason may hinge on the fact that nosema spores are pretty much everywhere, and a strong colony can often overcome the disease. Maybe they don’t think it’s worth the effort.

      The main thing is determining if it’s nosema or just dysentery. When you pulled the sample, did you see any spores? If not, you can just clean up the hive and reuse it. It sounds to me like you might have gone queenless at some point during the fall, which is not at all unusual these days.

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