What to do with moldy combs
A few years ago a beekeeper friend announced to me that mold had taken over her hives and killed all her bees. Now whenever I see moldy combs—or even hear about it—I think about her. When I tried to explain that it was the other way around, that the bees died and then the mold came, she didn’t believe a word of it. She cut out all the combs and washed the frames with bleach. Too bad.
A variety of molds will grow on the combs when the moisture in the hive gets too high. The moisture gets too high when there are not enough bees to fan it away. I suppose the confusion arises because these moldy combs frequently contain dead bees that are also covered with mold, so it looks like the mold killed everything.
According to various sources, one of the molds frequently found on combs is Penicillium waksmanii which can actually inhibit the growth of certain bacteria, including American foulbrood. Other molds are usually present as well, as evidenced by the different colors—usually blue, white, yellow, or gray.
If you have a dead hive loaded with mold you will be tempted to discard the comb, but it is usually not necessary. The first thing you need to do is decide how the colony died or became weak. If you can eliminate American foulbrood and Nosema ceranae, then you can re-use the combs.
How to prepare moldy combs for new bees
The first thing to do is take the frames to a warmish, dry place where they can dry out for a few days. These things can smell wicked—like moldy stuff does—so put them in a place where they won’t bother you. Separate any frames that are molded together and let them air dry. As they dry the mold growth will slow down and then stop.
Once the combs are dry you can store them in an empty super. As your colonies build up in the spring, you can place the moldy super on top of a big, vigorous colony and the bees will clean and polish every cell in a matter of a few days. Worker bees always clean old cells prior to re-use anyway, so this is not an unnecessary burden on the bees. The bees are very thorough. After they are done, the combs can be used for brood or honey production. It’s amazing, but no taste or smell of mold will remain on the combs.
If you have more than one colony, you can divide the moldy frames between them, or you can give a few at a time. I usually just put the whole box on a big colony and, by the time I remember to check, there is no evidence that mold had ever been there.
For a more thorough explanation of how mold becomes established in a hive, see “Physics for beekeepers: mold in a beehive.”
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