Waxworm damage to a beehive colony frame. Photo credit: Georgia Department of Agriculture, Bugwood.org
How To Stop 4 Pests From Damaging Your Beehives: Written by Ruth O’Neill. Ruth is a Research Associate in the Wanner Extension Entomology Lab at Montana State University, who cooperates on a variety of projects related to insect pests of crops. She has experience as a hobbyist beekeeper, and has a special interest in honey bee health and protection.
In the western U.S., as elsewhere, Varroa mites are among the most serious hive pests you are likely to encounter, and I talk about them in a separate blog post. In this post, I will cover problems with these four common beehive pests and talk about some solutions: ants, tracheal mites, wax moths, and mice.
Raiding ants can be a serious problem in beehives, stealing food stores and brood. The most effective approach is both inexpensive and pesticide-free: ant barriers. There are several types, all equally good at excluding ants from your hives, but each with a few drawbacks to consider. In addition to barriers, there are a few other deterrents worth considering, as well as some well-targeted pesticides that are worth mentioning. I describe these approaches below.
Types of ant barriers
Please note: Barriers only work if you clear out all grass stems and other vegetation touching the hives, or the ants will use them to get around the barriers.
Oil moats: Make a pair of 2×4 support boards for your hive. At both ends of each board drill a hole and put some long bolts or heavy-duty screws into the wood, so that the heads stick out several inches. Get four tuna fish cans or PVC caps and fill them with ¼ – ½ inch of vegetable oil, and stick the heads of the bolts into the can/cap, creating little moats around each leg. Drawbacks: Rainwater may wash out the oil. You’ll have to clean out and refresh the moats once in a while, and you will lose a few bees in them, but no ants will get past the moats if you keep them clean.
Sticky barriers: Coat the legs of your hive stand with Tree Tanglefoot (a sticky petroleum gel that can be purchased at any hardware store) or used motor oil. Drawbacks: Barriers have to be refreshed frequently, because as dirt and dead insects build up the ants can walk across them. Some bees will be killed.
Many beekeepers claim that cinnamon oil, spread around the hive stand and entrance area, is an effective ant deterrent. Essential oils, like wintergreen or peppermint, can be distributed on top of the frames inside the hive to discourage ants.
Pesticides for ants
Conventional pesticide sprays are not recommended in a bee yard, and more targeted and safe approaches are available. You can put trays with ant granules (there are many brands) under the legs of the hive stand, so ants have to traverse them to get to the hive. The ants will carry the granules back to the nest, where other ants – including the queen – will be poisoned.
If you can find the ants’ nest, you can pour one or two gallons of soapy water over it. Soap acts as a repellent; and, the soap also ruins the waxes in the ants’ exoskeletons, causing them to dry out. Another approach is to use outdoor ant traps; some beekeepers claim to get good results using them.
Tracheal mites are an internal parasite of honey bees. They multiply and feed within the breathing tubes of adult honey bees, mainly those tracheal tubes located in the first segment of the thorax. Workers, queens, and drones are all susceptible to tracheal mites. Peak numbers are in the winter and the early spring, and at these times colonies can weaken significantly due to reduced brood rearing and reduced bee longevity.
Because they are so small and easily overlooked by beekeepers, the importance of tracheal mites to bee health is probably underestimated. The only sure way to detect tracheal mite infestation is to freeze a sample of bees or kill them in alcohol, and dissect the bees’ thoraxes for examination with a higher-powered hand lens or a dissecting microscope. Older bees, which can be collected outside the hive, are the best subset to sample from. Many of the pesticides that are used to control Varroa mites will also kill tracheal mites.
Wax moths are a problem most often related to poor storage practices. They primarily infest unused supers and frames. The larvae (“waxworms”) are the problem. They spin silk tunnels on the frames, and feed on wax, pollen, honey, dead bee larvae – everything.
They’ll also invade active hives that have weakened defenses caused, for example, by low numbers due to recent swarming, loss of a queen, disease, or cold temperature inside the hive. Workers in strong colonies remove wax moth larvae and repair damage promptly. There are actually two species (Galleria mellonella and Achroia grisella), but from the beekeeper’s perspective the difference is not important as they share the same life habits and the larvae look very similar.
To prevent waxworm problems on your stored frames, scrape off propolis (a red/brown material comprised of plant resins and beeswax that bees use as glue) and brush the frames off, then put them back in the supers. Put the supers in plastic garbage bags sprinkled inside with moth flakes (paradichlorobenzene) and tie them shut.
Rodents and shrews:
Mice, voles, and shrews are a common problem in the winter, when the hive is vulnerable to attack because the bees are tightly clustered and unable to guard the hive entrance. Mice and voles are more indiscriminate feeders, eating stored honey and pollen, and chewing into the comb. Shrews are insectivores, and their attacks focus exclusively on the worker bees, often leaving dead bees with their heads chewed off, or their thoraxes hollowed out.
Rodents and shrews can easily be excluded from overwintering hives with an entrance blocker that screens them out. Care has to be taken to make the holes big enough for bees to get through without scraping off their pollen (yes, they will forage in late winter/early spring on willow flowers etc.), yet small enough to exclude even shrews. The recommended hole size for the winter entrance system is 3/8”.