honey bee management

The value of a postmortem

One of the worst mistakes we can make—in any endeavor—is failing to learn from our mistakes. But we can’t learn until we know what went wrong, and that is the job of the postmortem. But beekeepers frequently assume they know what killed a colony without actually doing the leg work to prove it. I’ve done it, and many others have done it as well.

Here’s an example: It was a cold and blustery winter in the mid-Atlantic when Fred’s two hives died. When he looked inside, he saw lots of honey and two small clusters that looked like they froze to death. His conclusion: the bees weren’t warm enough. Next year he will add more insulation, moisture boards, tar paper, and whatever he can think of to prevent his colonies from freezing to death. He might even add a terrarium warmer and put them in the garage.

Now if this fictitious beekeeper had actually done a thorough postmortem, he would have known that although his remaining bees ultimately froze, that’s not what doomed the colony. A bumper crop of parasitic Varroa mites had been living among the bees as evidenced by copious bundles of guanine left in the brood cells. The mites killed many bees by sapping their strength and delivering viral disease until the colony was no longer large enough to keep itself warm, so the remaining small cluster did, indeed, freeze.

But by naming the wrong cause, the cold, Fred is destined to make the same mistake again—ignoring the mites. All the insulation, heaters, moisture control, and babysitting in the world won’t help if mites are taking over the colony.

No matter when your colony dies, it is fitting to do a postmortem. Even if you don’t know what the signs mean, make a note of them, take photos, or both. Later, you can get someone to help you analyze what went wrong so you can do something different next time—the right something instead of the wrong one.

Look for honey stores, pollen stores, brood. If brood cells look abnormal, note that. If they look normal, open a few. Do the pupae look normal? Do you see mites? Look at bottom board debris: What is it made of? Is anything living in it? Are dead things in it? Look at the top bars: Is bee feces evident? What about beetles?  Wax moths? Yellowjackets? Mice? Are frames moldy? Is the interior wet? Was the hive robbed? Is there a cluster of dead bees? Where is the cluster in relation to the nearest food? Look for signs of disease. Look for guanine deposits. Look for deformed wings. Record it all, no matter how insignificant it may seem.

I used the example of cold bees for a specific reason. I believe that most colonies belonging to hobby beekeepers die from two things: starvation or Varroa mites. I also believe that few colonies that are well fed and mite free actually die from cold. To a robust colony, the cold is almost a non-issue, especially if the bees are dry. But even a little moisture shouldn’t be life threatening to a strong colony.

That’s not to say there aren’t other reasons for colony demise—there are many—which is why a good set of observations can make you a better beekeeper the next time around. Don’t let first impressions fool you: always dig deeper.


What does it all mean?

What does it all mean?


  • If the cause is actually Varroa, what do you recommend? I get conflicting info from beekeepers in this area. The bee club that my mother goes to are big on natural solutions and avoiding chemicals. The bee club closer to me is heavily sponsored by the local bee supply store and the two main keepers that speak are commercial keepers and are quick to throw Apiguard, Apivar, Terramycin (for AFB), and whatever else you can think of to ward off bee pests.

    I have a feeling there’s a middle ground. But what is your opinion? When should you just let Darwinism play out and replace bees that aren’t fending off the pests and when is that just not financially feasible to do?

    • Chris,

      I can’t answer your question because I believe that how a beekeeper handles mites, whether he uses hygienic bees, mechanical separation, hard chemicals, or so-called soft treatments, is an entirely personal matter. On the other hand, I believe that a beekeeper has an ethical responsibility to do something—to pick one or more options and run with it. I believe if you decide to keep bees you have a duty to care for them, and singing praises to Darwin with some idea of survival of the fittest just doesn’t cut it.

      Not that it matters but because you asked, I use a rotation of soft treatments: HopGuard, ApiLife Var, and oxalic acid.

  • I too was confused about how to deal with mites, and the local club had some very forceful advocates for treatment free. I found that IPM strategies, while useful, were not sufficiently effective for me. By the beginning of their second season, the bees were heavily infested with mites and two colonies collapsed from overwhelming mite damage to brood early in the spring. I immediately applied formic acid (MAQS) as it was just warm enough out to use that product and was so pleased with the results I will do that again this fall, and/or an oxalic acid vapour in midwinter.

    One problem with the full suite of IPM strategies, including the use of brood breaks and targeted splits, was that it required more equipment, time, and beekeeperly wisdom than I had as a young-in-years beekeeper.

    • Western,

      This is an excellent observation well stated. Let me add that when I had two or three hives, IPM seemed like a good answer. When I got up over twelve, there simply weren’t enough hours in a day to take the required steps. Like anything else, there are give and takes when it comes to a mite control strategy.

    • Danielle,

      Mechanical separation means separating the mites from the bees by physical rather than chemical means. Examples of mechanical separation include powdered sugar dusting, drone trapping, queen sequestration, splits, and screened bottom boards. Usually such techniques have to be used in combination because any one won’t be enough to suppress the mites.

  • I saw you mentioned yellowjackets. This is my first year keeping bees. We suddenly have a yellowjacket problem in our yard. I think I successfully eliminated one hive via the soap and hot water method read about. We have not yet located the second hive. My husband and a friend were both attacked by the yellowjackets and I have read they are a danger to honey bees also. Is that true and do you have any further suggestions on eliminating the problem?

    Thank you for your time and help!


      • I remember reading that. And I think that other article came to the same conclusion, although they really didn’t theorize much about the “whys”.

        I’ve got a couple of those green drone frames that I bought for varroa control earlier in the year. But never needed throughout the summer. It wasn’t until about 2-3 weeks ago when I harvested honey that I witnessed varroa on one hive. It looked pretty bad, but then 2 weeks later, there was nearly none. I had to look hard to find a bee with signs. I don’t get what happened. My guess is they were there, I just didn’t see them this last inspection.

        Anyway, varroa treatment of some type is on the to-do list now. I just don’t know what I should do. I don’t want to over-react and do more than I should. But you’ve got me nervous about doing too little now.

  • What do you mean by copious amounts of guanine? Guanine is one of the four main nucleobases found in the nucleic acids.

  • Well then, my hive has them too. I am not far from SF – I live in Redwood City – which is about 30 miles south of SF. I trapped a bee that made it into my house after buzzing around my flood light. I noticed 2 or 3 of these pupae in the bottom of the cup after a few days.

  • Sightly on topic, slightly off topic. I’m not a beekeeper, but I want to be. A friend introduced me to a man who was looking to get rid of some bee hives, frames, tools, etc, all of which are fairly new. The man said that bee keeping was something he and his ex wife did together and after his bees absconded (he said both hives up and left) he wasn’t interested in continuing to keep bees.

    He offered to sell me all his stuff for really cheap. I said sure, and figured if I could get started for a lot cheaper, why not. The hives are dusty but in good shape, same with the frames. Most have plastic foundation with no comb on them. A few have very little drawn comb, and a few that I didn’t notice initially when I inspected the hives, had some dark substance on some of the plastic cells of the foundation. Many of these darkened cells (no comb, just the the base cells on the foundation) are dark and shiny, but I noticed that several of the dark foundation cells have some dark brown crusty crumbly looking substance on the cell. I don’t know what it is and now I’m concerned that the reason why he was selling this stuff so cheap was that the hives died from some disease.

    I initially asked him if his bees had died of a disease and he assured me that they had all flown away when he neglected them in the winter. He said he left too many supers on the hives in winter and that the bees couldn’t keep it warm enough, so they left. Thinking about it though, last year in northern California it was a really mild winter. It never got very cold.

    I plan on cleaning everything with bleach anyways, but I don’t want to get bees next spring, just to have them succumb to a disease from the hives I put them in. How can I know for sure if the hives are safe? Is there a way I can post a picture of the foundation with the crusty brown stuff on it to see if anyone knows what it is? Thanks for any tips you can give. As someone looking to get into beekeeping this site has been an awesome resource

    • Mark,

      It doesn’t sound like a disease to me. The brown flaky, crusty stuff is probably pollen. Based on your description, I won’t worry about it for two seconds. Most of the bad diseases are brood diseases, and you won’t see them on undrawn foundation. If there is very little drawn comb, I’m not surprised they absconded. It sounds like they didn’t get going before winter and tried to move somewhere else. You can send a pic if you want to rusty[at]honeybeesuite[dot]com.

  • Hi Rusty,

    I’ve been beekeeping for the last 2 years, and I have lost my hives each year. The first one was due to a bear destroying everything, and in the fall, I had one dead out, and one strong hive, and one that we rescued from a tree someone had cut down. This spring when it was warm enough to check on them, I found both hives dead. The strong hive had evidence of a mouse, and when we took it apart, we found a mouse nest, and what looks like bee defecation on the tops of the frames. You can smell the mouse next, but it does not have the smell of rotting meat, or any other foul odor.

    Can I reuse the frames with the honey and wax for my new nucs that are arriving sometime this week? The small rescued hive died of not enough ventilation, and has green mold on everything. I’ve read your blogs, and you say I can wipe the mold off the tops and bottoms of the frames, and give them to another hive to clean, so I will do that when we get our new bees. I know that I need to keep trying to make these little critters live, and I love beekeeping, but it is discouraging at the same time. Do you have any suggestions for me? Does it sound like I am able to reuse both hives?

    • Maryanne,

      It sounds like you can reuse both hives, and the bees will clean up the mold. I’m a bit skeptical about the causes of death, however. A mouse usually won’t wipe out an entire colony. I trapped a total of four mice this year from one colony, and the bees are doing fine. Mostly they just screw up a frame of two, but the colony lives on.

      The same with the small colony. Mold happens after the bees die, not before. Did you do mite checks in the late summer, early fall? I would be very suspicious of something like mites, but since I don’t know how you managed them, it’s impossible for me to say.

      • Actually Rusty, the small hive had both small hive beetles and wax moths, which I think we got rid of before fall really set in. I did not check them for mites, which thinking back, I should have, but I didn’t see any on the bottom board when I checked them in the fall. They were in a small cluster when we took the hive apart so I’m pretty sure I had just too much moisture and failed them by not having enough ventilation. I did check the large hive for mites, and didn’t find any, but I am still learning, and I will keep trying as long as I can to have bees and keep them alive.

        Thank you so much for your insight and help, I really appreciate it!

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