Will Wax Moths Come up Into the Hive From the Screened Bottom Board?

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Will Wax Moths Come up Into the Hive From the Screened Bottom Board?

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Dave D writes:

Will wax moths come up into the hive from the screened bottom board? I’ve cleaned up some deadouts and would like to leave them set up, the freezing during the winter should have killed eggs or larvae in the comb. I’ve closed off the entrances with window screen.

Rusty Burlew replies:

Since I don’t know the size of hardware cloth in your screened bottom board, it’s impossible to say if an adult greater wax moth, Galleria melonella, could squeeze through it. Most of the commercial screened bottom boards use size 8, which is eight squares per inch. Of course, the squares’ diagonal measurement is longer than the side measurement, giving them extra wiggle room.

I asked around a bit, and the beekeepers I talked to agreed that size 8 will block most, but probably not all, greater wax moth adults. As with any animal, there is a natural variation in the size of individuals, so there’s a chance that some will squeeze through. Another variable is the thickness of the wire used to make the hardware cloth. A thicker wire leaves a smaller opening.

However, the lesser wax moth, Achroia grisella, will have no problem with a screened bottom. They are much smaller than the greater wax moth and often inhabit stored combs, where they eat cocoons, bee feces, bee parts, and pollen. Both types of wax moth are attracted to combs for what they contain, not for the wax itself.

If you want to keep both types of moth out of your stored hives, try cutting a layer of window screening to lie atop the screened bottom board, or use the slide-in varroa tray that comes with most commercial bottom boards. Alternatively, you can force-fit a piece of regular cardboard either above or below the screened bottom, something I do for short-term storage of just a few months or less.

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