Protecting Comb From Wax Moth

Bridget Beattie

Bee Craft September 2011

There are two species, commonly known as the Greater Wax moth and – wait for it – the Lesser Wax moth. Their Latin binomial names are Galleria mellonella and Achroia grisella respectively.

Why are they important, these dull relatives of butterflies? Because they live in hives and given half a chance will munch away at honeycomb. Let’s have a look at what happens in a wild colony which makes wax moths beneficial insects.

In a wild bee nest, comb is built and used for brood and storing pollen and honey, and when it gets a bit manky, the bees have the space to move along and build a new comb while the oldest ones are put out of use. In this way the colony keeps its combs clean and reduces the build-up of disease organisms as well as avoiding excessive pupal skins. When an adult bee emerges from the cell, it leaves behind its pupal sac which is not removed by house bees. They clean out the inside ready for a new egg but after several rounds of brood, the cell contains several layers of discarded skins. Guess what. Wax moths love it. As the bees move along onto new comb, wax moth larvae get busy and demolish the old combs, munching away and at the same time removing disease organisms and old dark cells. Strong colonies do not tolerate wax moth in their midst on current combs but on the old disused or abandoned combs they leave them to get on with it. Furthermore, if a colony dies out or absconds from its home, wax moths move in, clean up, a new swarm takes up residence and the housework has been done for it including a good deal of disinfecting. Neat.

Wax moth cocoon and larvae. Photograph: Margaret Cowley

Wax moth cocoon and larva. Photograph: Margaret Cowley

So in the wild, wax moths perform a valuable service to bees.

 Ah but. Most beekeepers use hives with open mesh floors. There is a sliding tray which fits under them to check for dead varroa mites. If the tray is left in for longer than necessary for monitoring varroa levels, wax moths invade below the mesh floor and bees cannot get to them to clean them out. Now I know some people are uneasy about having bees on open mesh floors as they think that the bees are too cold or too ventilated so they leave the trays in. This defeats the purpose of having the floors except for varroa monitoring and if trays are left in they MUST be cleaned out regularly, which means at least every week. If you are uncomfortable, change the floor to a solid one after the last varroa check, and re-install the open mesh when you again need to check in spring. Some beekeepers put an empty super under the open mesh floor, creating a space which they feel gives some protection from the wind in winter.

Wax moths do damage to stored frames in a big way, especially the Greater Wax Moth. The adult moth does no damage but when the eggs hatch into larvae, they spin a little webbed tunnel through the comb and feed voraciously. They eat the remains of the pupal sacs and faeces in the brood comb as well as pollen, so it is the brood combs which are most at risk and wax moth larvae can very quickly completely demolish combs. Then when the Greater Wax Moth larva pupates, it gouges out a groove in the wood of the hive. When there are many, the cumulative damage to wooden hive parts can be enough to render them unusable so not only do we lose the comb in the frames but the more costly wooden parts are also destroyed.

If they do get a hold within a colony, wax moth larvae can spoil the supers too by their tunnels and by leaving behind their own faeces – these look like little black specks. It is a good idea to extract supers as soon as they are removed from the hive, not just because it’s easier when they are warm and less likely to granulate too soon, but because wax moths do find their way into stacked full supers as well as extracted ones and can ruin some of the crop.

So what to do to prevent wax moth damage?

After the supers have been cleaned up, they must be stored safely in a clean environment because, after all, they are used to produce a food. They can be kept indoors or in a shed or garage, in which case they should be completely sealed so that wax moth cannot enter. Bear in mind that if they have been in a beehive, they may well have the almost invisible eggs on them….Alternatively, because freezing temperatures will kill them, they can be stacked out of doors but make sure they are bee proof.

There is a biological control available which is a bacterium called Bacillus thuringiensis, marketed as Certan or Mellonex. This product is used to control caterpillars on agricultural crops too as it is specific to the insect order Lepidoptera ie butterflies and moths. It comes as a powder which is mixed with water and sprayed onto each side of the frames. It will give very effective protection to your stored frames.

If you do find your frames have an infestation of wax moth, clean them up and put in new foundation. Frames come up beautifully when simmered in hot washing soda solution.

Otherwise – well –  I have a friend who goes fishing and swears by the maggots. You could always go into bait production instead of honey!

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