09/25/2026
The number 1 killer of honeybee colonies is a devastating parasite of the bee broodnest: Varroa Destructor Mite.
In the Fall the varroa population in the hive balloons. This parasite can easily overwhelm a colony and result in a complete loss in a very short period of merely a couple of weeks.
Left untreated; A strong hive goes to nothing by Thanks Giving.
Left too long before treating for mites; A colony that has been “injured” by a high varroa mite load and the virus’ that it carries is usually dead by Christmas and rarely lasts past mid February.
There are various tools and regulator approved treatments to control this parasite. None of them are easy and none of them are entirely effective. All are high effort with partial results. It is a very VERY difficult balancing act. How do you kill a flea on a bee without killing the bee??!! That is the challenge that apiculture researcher and every beekeeper has been trying to solve.
One method that I prefer to use in the Fall is to fumigate the colony with a vapour created from heating oxalic acid crystals. (OAV). The OAV “smoke” is injected through the entrance and left to fill the cavity of the hive. As it cools the OAV condenses forming microscopic crystals on surfaces inside the hive and on the bodies of the bees. The feet and mandibles of the varroa mite are sensitive to this acid which causes them to detach.
The bees are mostly unbothered by the oxalic acid as it is a naturally occurring (organic) ingredient of many of the plants and flowers which the bees forage on and make honey from. Yes, that means oxalic acid is a natural ingredient in nectar and honey, and a natural “organic” treatment to use against the mites.
Bees regularly groom themselves and each other. The injected OAV crystals condense on the hairs and bodies of the bees. The bee in this video is white with OAV crystals. You can see her grooming. As they groom they wipe the OAV off of themselves and with it the mites also get removed.
Each mite control method has its pros and cons. OAV is very effective at removing varroa destructor mites. 100% removal when done correctly. However! - the OAV regimen does require a commitment to a strict schedule of multiple visits and applications to the hive to catch mites between egg through brood capping. The timeline must extend over the span of an entire brood cycle of 21-24 days. Once you start OAV you are committed to a 5 day interval for 3.5 weeks. OAV is NOT a one and done treatment. And, if you miss a 5 day slot in the middle - you have to reset the calendar and start over.
Fellow beekeepers … what do you do to knock down the mites and protect that crucial winter bees brood being raised right now?