Wax moths are an ever-present threat to beeswax, but they are easy to manage as long as you understand the enemy you're fighting, use the correct tools, and work with your bees to keep their precious wax safe.
Wax moths are actually two species of moth: the Greater wax moth (Galleria mellonella) and the Lesser wax moth (Achroia grisella). Even though these moth species aren't that closely related to each other, their behavior (and impact on a frame of wax comb) are so similar that they're usually treated as one pest by beekeepers. Both species can be found throughout all of North America, but the Greater wax moth (in part due to its larger size) causes the vast majority of the trouble.
The moths have a remarkable ability to smell beeswax. Using their finely tuned antennae they can pick up the smell of a colony or empty hive even from great distances away. At night the female moths sneak in and begin laying eggs, hundreds per moth over their lifespans. As the eggs hatch, the larvae eat through the combs, devouring wax, stored pollen, pupation residues left behind by bee brood, and other hive detritus that the young moths use to fuel their growth. The wax itself can be broken down into energy by the young moths and turned into fat, but their protein comes from all of the other stuff they eat. This is why moths often prefer to lay their eggs on darker, dirtier frames.
Of course, ideally, the moths will be completely excluded from your hives in the first place. If no moths can get in to lay eggs, there will be no wax moth larvae to deal with later. A strong bee colony can and will exclude wax moths, and will also remove their eggs and larvae if any make it inside the hive. A colony that has been weakened by anything else (like mites, mite-associated viruses, fungal or bacterial diseases, queenlessness, dehydration, pesticide exposure - the list goes on), may become unable to resist infiltration by wax moths. Keeping your colony strong and healthy is the single best thing you can do to combat wax moths.
Weak colonies will sometimes give up the battle against wax moth infestations, and as the bees die from their preexisting condition the moths are left to run rampant. When beekeepers tell us that wax moths killed their colony, we usually discover that the real culprit was really untreated varroa mites, and the moths just made a mess of things as the colony died. If there is too much comb area for a small or sickly colony to patrol and guard, they won't be able to suppress the growth of young wax moths that will start munching their way through the combs.
Letting healthy bees protect their own wax is a good practice, but sometimes we have to store frames away from the watchful eyes of our patrolling bees. When you remove frames of comb from your hives and put them into storage, you should assume that you ALREADY have wax moth eggs on the frames. Therefore, sealing the combs up in wooden boxes or plastic bags will not protect your combs. You need to kill any wax moths that are already there, and the best control plan will also kill future wax moths that may find your equipment.
One method to kill wax moth larvae, pupae, and adults is to freeze the combs. A thorough freeze will kill moths, and if no new female moths get access to the combs your equipment will be safe. However, not all of us have a spare walk-in freezer to freeze our combs. And no matter how well-sealed we think our previously frozen frames are, enterprising moths will still sometimes sniff them out and get in. Other moth-control methods that provide residual control to stop newly arrived moths therefore offer better protection than a single deep-freeze. Most of us can protect our combs during a cold winter by allowing frames to freeze in our garages or bee sheds, but moths should be on your mind as soon as the weather warms up. Otherwise stored combs (as well as hives whose bees didn't make it through the winter) are ripe for invasion by new moths.
One tempting method to kill wax moths is to dig up those old mothballs you have stuffed in a closet somewhere. If they worked to keep grandma's sweaters safe from moths, surely they'll be tough enough to kill wax moths too? Well, the good news is that most mothballs (active ingredient: Naphthalene) do kill wax moths. The bad news is that they also permanently contaminate wax comb, and are toxic to bee brood AND to humans who might eat honey from those combs. Naphthalene mothballs are the wrong choice for wax moth control, even though they are able to kill wax moths.
However, a few commercially available moth balls don't use Naphthalene, but instead use a chemical called para-Dichlorobenzene (or PDB for short). We don't recommend using such mothballs, because they aren't manufactured specifically for use in honey bee hives (which means they could contain trace contaminants that are safe for your sweaters, but unsafe for your bees or honey customers). The chemical PDB is also the active ingredient in Para-Moth moth crystals, a wax moth control product for honey bees that safely protects bee-less frames of wax. The crystalized PDB is put on a piece of scrap paper or plastic on top of a stack of hive bodies full of frames. As long as cracks and gaps are taped shut or plugged up, the PDB will slowly vaporize and fill the stacked equipment, killing moths and repelling new female moths from entering the stack. Frames treated with Para-Moth just need to be thoroughly aired out to allow the chemical to evaporate away before the frames are given back to the bees.
Another exciting moth control option is marketed under the name Certan. It is also called "B402" in the United States, to distinguish it from the older formulation marketed as "B401" in many other countries. Whatever the name, the mechanism of action is the same: The frames are coated with a specialized strain of the bacterium Bacillus thuringiensis, or "Bt." This specialized strain produces a protein that binds with the stomach cells of young wax moths and destroys them, killing the larvae. If the same protein enters the stomach of a bee (or a person) it has nothing to bind to, so it causes no harm and is simply digested like any other protein. Certan can be slightly more laborious to apply (the liquid must be spread over each comb) but treated combs don't pose a health risk to the bees and don't need to be aired out before honey is produced in them. After diluting the product according to the instructions, we put it in a spray bottle to coat both sides of our frames.
One great way to keep moths away from your hives is to never leave unguarded wax nearby. Since bees don't spend much time patrolling the bottom of their hive, regular cleaning of bottom boards (and particularly underneath screened bottom boards) can eliminate potential food for baby wax moths. Likewise, unwanted burr comb flung into the surrounding grass won't kill your lawn, but it may attract a female wax moth. If she fills that scrap of comb with eggs, a whole new generation of moths may be born right in your apiary. Instead of throwing scrap combs near your hives, consider disposing of them in the trash, or investing in a solar wax melter to harvest all of that scrap and turn it into usable beeswax.
The final important part of wax moth management is knowing when you've lost the war. Sometimes frames with moth damage are simply too far gone, and it's not worth the time, expense, or heartache of trying to save and salvage them. Maturing moths damage wood (leaving behind canoe-shaped gauges) and combs covered in moth silk and feces may present more work to your bees than a new frame that they must build up from scratch. If moth damage is minor you can pull moth silk and frass (moth poop) off of the combs and allow the bees to repair them. The more extensive the damage, the better it may be to simply discard the combs and resolve to be smarter about fighting off wax moths in the future.
The very best way to keep wax moths under control is to keep your colonies so strong and healthy that they can easily fight off the occasional moth. Preventing moths from breeding on scrap wax will also protect your bees. Since most of us have to store frames away from our bees at some point, it's often worthwhile to have a moth control chemical on hand to make sure your frames are safe. Whatever moth-control method you choose, make sure you're ready to protect your stored combs right now, so that you aren't waiting for a shipment of moth-control chemicals to arrive as moths multiply in your stack of stored frames.
For even more tips about moth control and a demonstration of how to use the moth treatments in this article, check out this video on our YouTube page. (Don't forget to like and subscribe!)