honey bee threats

Secrets to freezing wax moth eggs: your results may vary

You can kill wax moth larvae, as well as adults and eggs, by freezing honeycombs.

If you want to get rid of wax moths and their young on honey combs, just freeze the entire frame. But keep in mind, the time required to kill them depends on your freezer.

Inside: It seems everyone has a different recommendation for how long you need to freeze honeycombs to kill wax moths and their eggs. The reason: all freezers are different.

Killing wax moth eggs requires a hard freeze

This morning a reader pointed out inconsistencies on my website. In one post I wrote, “Freeze honey combs before storing. The USDA recommends 24 hours at 0 degrees F.”

In another post I write, “To kill the moth [eggs], you must monitor both time and temperature. For example, the Mid-Atlantic Apiculture Research and Extension Consortium (MAAREC) publishes the following guidelines to kill both species of wax moth: “20 degrees F for 4.5 hours or 5 degrees F for 2 hours.”

The reader wanted to know, “So which is it?”

The real answer varies with every freezer

The real answer here is “neither” or “both,” depending on how you look at it. These numbers—like so many others in beekeeping—are recommendations or guidelines. They are not rules carved in stone. You’ve certainly heard advertisements that end with the phrase “results may vary,” right? Well, that applies to nearly any beekeeping recommendation, including these.

Most of the time, science doesn’t reveal simplicity. Instead, it exposes complexity. In a simple situation like freezing wax moth eggs, there are far too many variables to give a cookbook answer.

I had a statistics professor in graduate school who loved the word “exogenous.” He would stand in front of the class and hold on to the second syllable as long as he could: ex-ahhhhhhh-gen-ous. His point was that nothing goes uninfluenced by other things. So when your experiment doesn’t work, you say “Ahhhhhhhh! It’s those ex-ahhhhhhh-gen-ous variables!”

So what is an exogenous variable?

Simply stated, an exogenous variable is something that originates from the outside. In this case, factors not measured or considered in egg-freezing experiments are affecting the results.

The examples listed above show the times and temperatures needed to freeze wax moth eggs in two different freezers in two different places by, I imagine, two different researchers.

That the results are different is not at all surprising. Of course they are different. If they were the same, I wouldn’t trust either of them. Exogenous variables, variables not measured in the experiments, affected the results.

Name a variable that might go unmeasured

Now, I don’t know what those variables were. There are probably many, but over breakfast this morning we came up with some possibilities.

    • Thermometers: they read differently. Go to a store display of thermometers and take a look.
    • People: some may read the thermometer carefully, some may round, or there may be parallax.
    • The temperature of the freezer: is it close to your target temperature or much colder?
    • The freezing cycle: how warm and how cold does the freezer get during each cycle of operation?
    • Defrost cycle: if the defrost cycle runs when the frames are in there, freezing will take longer.
    • Temperature of the combs going in: if they are 80 degrees, freezing will take longer than if they are 60 degrees.
    • Opening and closing: if the freezer is opened frequently, freezing will take longer.
    • How deep in the freezer are the frames: deeper placement means less influence from opening and closing.
    • Packing arrangement: If frames are packed tightly, freezing will take longer.
    • Condition of the freezer gasket: if it’s old and worn, it may leak, so freezing takes longer.
    • Amount of frost in the freezer; frost is an insulator and could change the rate of freezing.
    • Front near the gasket could create an air leak and decrease the rate of freezing.
    • Size of the load: if you add many frames at once, they will take longer to freeze.
    • Thickness of the combs: thicker combs will take longer to freeze.
    • Frame wraps: if you wrap the frames heavily, they will take longer to freeze.
    • Condition of moth eggs: are they full of water or are they beginning to dehydrate?
    • Mass of freezer contents: if lots of frozen goods are in there, the new additions will freeze faster.

I’m sure you can think of others. But as you can see, it would be impossible to calculate all the influences. Instead, we write guidelines that work for most people most of the time. Are they failsafe? Of course not.

How can I make sure the moths are dead?

People often ask how I do it. In truth, I don’t monitor the time, temperature, or anything else. I wrap my frames in plastic film and then place them in the freezer overnight. The next morning, I take them out. Without removing the wrap, I let them thaw at room temperature and then store them in a cool room. Period. I’ve never had a problem.

But my freezer is a big, deep chest freezer with lots of frozen stuff in it. Yours will be different. If you think the freezing was sufficient to damage the wax moths eggs, you are good to go. If not, leave them in longer: f Freeze them until they are hard. Freezing them longer won’t hurt anything at all.

Honey Bee Suite

Freezing wax moths eggs prevents the growth of larvae.
Freezing wax moth eggs prevents the growth of larvae. Wax moth larvae are an unpleasant addition to your comb honey, although I hear they are good for fishing. Pixabay public domain photo.

About Me

I backed my love of bee science with a bachelor’s degree in Agronomic Crops and a master’s in Environmental Studies. I write extensively about bees, including a current column in American Bee Journal and past columns in Two Million Blossoms and Bee Craft. I’ve endured multiple courses in melittology and made extensive identifications of North American bees for iNaturalist and other organizations. My master beekeeper certificate issued from U Montana. I’m also an English nerd. More here.

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  • You said: “Wax moth larvae are an unpleasant addition to your comb honey, although I hear they are good for fishing” You under-estimate the value of wax months and basically, the bees know how to handle them, because the bees know the benefits. I produce them by the millions…..

    • Richard,

      Hmm. I agree that honey bees can handle wax moths, but when your harvested comb honey is sitting on your kitchen table, there are no bees. Not in my house, anyway.

      • Don’t argue with know it all types. Most think their IQ is far higher; yet much lower than the norm for any education. Try placing both temps on a graph. Label one side with temp and the other in hours. Recommend an additional 10 percent on either side for a guarantee and don’t answer silly questions. If they can’t grasp such; they shouldn’t raise bees.

  • Wax moth larvae are just plain creepy! They also can and will chew through Ziploc bags if the comb is not frozen which I recently discovered. The wax appeared to be intact but crumbled to a fine powder when touched. Moths and larvae in all stages from wax comb removed from the hive in January. They are resilient, I’ll give them that.

  • Ha Rusty, why do u wrap your frames, do u or should u wrap them? This is what I do, am I messing up, I took out all the shelves in the freezer, I stick the whole hive body in the freezer it will hold 4 deeps and I let them stay in there for several days or weeks until I will need them unless I have a bunch to freeze then it is a week. my storage room is my living room

    • Frances,

      The reason for wrapping is storage. The freezing kills the eggs, but if the frames are stored where wax moths can reach them, they can be reinfected immediately by the next moth that comes by. If your frames are stored where no moths can reach them, then there is no danger of reinfection.

    • John,

      Very good point. The eggs of the different species will have different characteristics and different response times to freezing.

  • Hi Rusty,

    I’ve done the same thing as a moth preventative. Once a year I take as many frames as I can fit, wrap them (or not) and stick them in my freezer. 24 to 36 hours later, I take them out and put in several more until I’ve cycled through all of them.

  • Time and temperature have tremendous impacts. In the science of food preservation, it is well documented that you can pasteurize products at relatively low temperature, but it takes much longer to effectively destroy the pathogens you are worried about with a low temperature/long time regimen vs. a high temperature/short time pasteurizer regimen. It has been a long time, but I remember from food science classes in the 1970’s that there were studies done on destruction of trichinosis cysts/eggs in pork. I don’t remember the details, but it would take roughly a month to destroy the eggs in temperatures just below freezing while at below 0 F temperatures it might only take a couple of days for the same effective kill and at -20 F even less time. I would be very surprised if the wax worm eggs did not respond the same way.

    • Joe,

      That is an excellent example of a factor I did not include in my list. Thank you!

      • Have you ever seen anyone use a cooler with dry ice to freeze frames? Dry ice temps are -109F or below. In a well insulated cooler with a reasonable amount of dry ice, I imagine you could get the temp in the cooler down to -50F or so. Seems like that would kill the wax moth eggs in pretty short order. Another possible benefit is that as the dry ice sublimates, it will fill the cooler with CO2 gas, which has its own killing effect.

        Thoughts or comments?

        • Jan,

          I have never seen it done, but I think it’s an excellent idea. If you try it, please let us know how it went. Very cool (pun intended.)

          • I worked for a national brewing company for 34 years. Our parent company at one point sent one of their corporate entomologists to study the effects of fumigating our grain silos with excess CO2 from our fermentation process. One the principles that he taught us was that pure CO2, without ‘some’ oxygen mixed with it would put the target grain weevils we were targeting into a hibernation state. I don’t recall the % CO2 maximum that he recommended, but they dangled caged insects into the silo on a string every 10 feet or so, and we did get an effective kill, but had to use a venturi type gas mixing device and a small fan placed inside the silo. CO2, being heavier than air, was sent into the bottom cone of the empty grain silo, (approximately 80 feet tall), through the mixing device and the atmosphere was monitored periodically over the fumigation process. The bottom line was that corporate brewing did approve the procedure, but it took twice as long as chemical fumigation process, so we never really used it after the test was concluded.

            As I recall, the process took most of two weeks and if the CO2/O2 mix got out of whack it would have to start over.

            As far as the dry ice theory, I would trust the efficacy of the cold treatment for an effective kill more than I would trust the CO2 treatment generated from the dry ice sublimating into gas.

            • Joe,

              Yes, I agree with you. In addition, lots of insects have extremely high tolerances to CO2, but freezing–especially hard freezing–is more reliable. The dry ice idea could be a good alternative for those with only a tiny household freezer, so that’s why I like the idea.

              The silo experiment is fascinating, as are grain weevils. As are breweries.

  • Hey, Rusty

    Also pollen-mould can be killed be freezing. Pollen comb that is to be preserved for later, can be put in a freezer (below 0 d.) for a day or two. The pollen stays fresh thereafter.

    Jan Olsson, Denmark

  • Two quick questions, Rusty.

    Do you keep frames wrapped after freezing?
    Is it best to store empty comb in a dry but sunny location or cool storeroom?
    Is Nosema apis spores also killed with this freezing?
    Many thanks for your immensely informative posts, Rusty. You are teaching us a lot!

    • Mary,

      1. Yes. The idea is that they are protected from re-infection by wax moths as long as they remain wrapped.
      2. Empty combs are best protected from wax moths by exposure to light. Wax moths do not like light. Many people stack boxes in a criss-cross fashion so all the combs get light exposure.
      3. No. Nosema spores are not killed by freezing.

  • If you didn’t have a large enough freezer, could you use dry ice and a very good sealing ice chest? Dry ice would have the added benefit of raising the c02 levels as well as freezing cold temps.

    • Caleb,

      Dry ice would certainly freeze them. Some insects, honey bees included, have a very high tolerance to CO2. I’ve heard they can tolerate levels that would kill us, but I don’t know about wax moths.

  • We did studies in 80 foot tall grain silos (empty ) with CO2 as a fumigant. I don’t remember the % CO2, but our test organisms would go into a hibernation state if the CO2 got too high. Best kill based on the CO2 as the only agent was considerably less than pure. It would take about a week for an effective kill under optimum conditions.

    I would expect that the cold would be the primary killer in this case, but only testing would tell for sure.

    • Thanks, Joe. I wish I could remember where I was reading about CO2 and honey bees, but it’s not coming to me. What you’re saying here sounds about right.

  • Well, there is a mite tester that uses C02 to knock out the honey bees in a container and do a shake test that way. I have been seriously considering it because you just dump them back into the hive when you are finished and they just wake up and go back to work. I’m glad to know it wouldn’t cause them any brain damage from oxygen deprivation. Here is a video of the process:

  • I’ve lost 5 hives to these little demons in the last month or so. I’m a novice when it comes to beekeeping. Only had 8 hives. I froze my frames and hives for 6 days. After reading this article I’m thinking that’s enough? But I’m not sure how cold my freezer gets, it’s one from Lowe’s hardware, like you use in the house . I’m not sure if it gets down to zero. But I think after reading this that’s all I need to do?

    Thanks a lot for your information it helps. Side note. I put the infected hives out by the freezer away from any bees I knew of and when I came back two days maybe three days later to put them in the freezer I found that a swarm had set up home in one of my hives (but I didn’t understand that’s what happened ), I just thought feeding bees from other hives had come to scavenge. I tried to knock them off, and i did a lot of them but there was more there. As a matter of fact I put it inside and closed the freezer door. But then after thinking about how heavy it seemed I thought there were more bees then should of been feeding and it was kind of heavy. I didn’t want to kill that many ! So I took it out and took a closer look . So now I have a new hive that I’m going to transfer over into one of the frozen hives as soon as they thaw out.

    • Terry,

      Wax moths are opportunistic scavengers that take advantage of weak colonies. Strong colonies can keep them in control. I wouldn’t assume that wax moths killed your colonies, but they took advantage of colonies that were already weakened. All I’m saying is that you should evaluate why your colonies may have been weak in the first place.

  • Rusty,

    This past winter and spring I have been rotating through my freezer several sets of honey and empty brood frame that wax moths started briefly to inhabit. I was able to arrest the wax moth development but these frames incurred some damage to comb cells that one could expect from the burrowing larvae. If I have satisfactorily freeze killed (to the best of my observation) the moth in its various cycles, do I need to be concerned about the damaged comb cells. Will colonies receiving these FRAMES readily repair them or should I scrape out the areas damaged by wax moth activity.

    Thank you.


  • I just had a wax moth problem in a hive that I caught before it was too late. I put the frames in a cooler and finished up what I was doing and then put them in a garbage bag and then into the freezer. When I came back to clean out the cooler, several wax moth larva had fallen to the bottom so I decided to spray them with Clorox and close the lid. An hour later I came back and they were still moving around in the Clorox so I went and got some stronger mildew cleaner and sprayed them with that. Several hours later they were still alive so I wouldn’t underestimate the power of these little devils to succumb to anything.

  • Rusty,

    If one extracts a frame that had a wax moth surface trail (removed gently by hand) could the honey theoretically contain wax moths eggs? If so, what might one do with that bucket of honey?

    I was asked this by a newbie and thought I should consult with someone of much greater beekeeping knowledge such as yourself.

    • G,

      Sure. Theoretically, the honey could contain wax moth eggs or bee eggs, or some other type of eggs. But wax moths don’t lay eggs in the wax; instead, they lay eggs in cracks in the wooden parts of the hive, especially the frames. But any eggs in a jar of honey cannot survive because they will desiccate in the supersaturated solution. No one in a commercial honey operation is going to stop and check for eggs in the honey because it’s just not important, not a problem, and no one would ever notice. I bet lots and lots of honey has some kind of insect eggs in it. See “Insects that Feed Us.”