Why formic reaches what oxalic cannot
Formic acid works as a vapor. Once the strips are in the hive the acid evaporates and the fumes spread through the colony, including through the porous brood cappings, so mites feeding on sealed pupae get hit along with the ones on adult bees. That single property is what sets it apart. A well-run formic treatment can knock down the large majority of the mites in a colony in one go, with no broodless window required.
The temperature window is everything
Formic works by evaporation, so the weather sets the dose. The usual guidance is daytime highs of about 50 to 85 F (10 to 29 C) across the treatment. Below that the acid does not vaporize fast enough to do the job. Above it, especially over about 92 F (33 C) in the first few days, the release runs away and you risk brood die-off and the loss of the queen.
So check the forecast for the whole treatment window, not just the morning you open the hive. A hot spell landing on day two is the classic way a formic treatment goes wrong. If your summer runs hot, aim for a cooler stretch or the shoulders of the season and read the label notes on hot-weather application.
Formic Pro and MAQS
The two common formic products are both strips you lay across the top of the brood nest. Mite Away Quick Strips, or MAQS, run a shorter, harder course. Formic Pro is the newer version with a longer shelf life and a gentler release over a longer window, which most beekeepers find easier on the colony. Both are labeled to allow honey supers in place, which is the reason to reach for formic in the first place. Follow the label for strip placement, timing and super rules, since those are what keep the treatment both legal and effective.
Where formic fits in the year
Formic earns its place in two spots. The first is mid-season, when a summer mite count crosses threshold but you still have honey supers on and cannot use the products that wait for harvest. The second is the post-harvest treatment in late summer, when you need a fast, thorough knockdown before the winter bees are raised and the temperatures still sit in range.
It is less suited to the cold end of the year. Once nights turn cold the acid stops vaporizing, which is exactly when a broodless oxalic acid treatment takes over. The two acids cover opposite ends of the season between them.
Treat strong, and confirm it worked
Formic asks more of a colony than a broodless oxalic dose does, so put it on strong colonies inside the temperature window and follow the label to the letter. Then test. A mite wash two to three weeks after the strips come out tells you whether the treatment did its job. Every treatment can fail, and the only way to know is a count.
Sources and further reading
The method and limits here follow the guidance below. Your product label and local regulations always govern.
- NOD Apiary Products: Formic Pro application, the manufacturer instructions and temperature guidance.
- Honey Bee Health Coalition, Tools for Varroa Management (9th edition), for method selection and timing.
- Randy Oliver, Scientific Beekeeping: Formic Pro in hot weather.
- University of Guelph Honey Bee Research Centre, for method demonstrations.
Log the treatment, the temperatures and the follow-up count in your hive records. A formic result that failed in a heat wave is worth remembering next summer.