Varroa mites are bad for honey bees, there’s no doubt about it. The mites harm our bees by feeding on their fat bodies and spreading viruses, and as far as I’m concerned are responsible for a vast majority of “mystery” colony losses. Despite this, I don’t mind when I find mites in my hives. In fact, I start to get worried when I don’t. So why this apparent contradiction?
Years of monitoring mites has taught me that my strongest colonies have the heaviest mite loads, and therefore need the most intervention. This seems like a no-brainer—of course a colony bursting at the seams with brood will have more mites than one that’s struggling to build population. Capped brood cells are nurseries for mites, after all. As obvious as this should be, I’ve heard and read many accounts from beekeepers confounded by the loss of their strongest hive, based on the flawed assumption that a strong colony should somehow be able to fight off the invading varroa. In reality, there’s a direct correlation between colony strength and mite pressure.
So this time of year—late summer through early fall—I’m routinely testing hives for mite levels. I get a bit alarmed if I see levels up over 3-4%, and I make those hives priority for treatments. But I get far more nervous if I see a hive that registers 0%. Those hives also get priority—not for treatment, but for checking the status of their queens. Sometimes it just means the queen has stopped laying due to the nectar dearth, which happens. But usually there’s enough residual brood during those dearths to harbor at least some mites, so more often finding zero mites is a sign the hive has gone queenless.
A lack of mites in this hive was a warning sign
The graph above (full resolution) is from a colony I lost recently. The chart shows the measured mite levels over the last couple years, and everything looked great until it took multiple attempts to successfully requeen after a split in April. But it provides a good comparison of mite levels in a healthy queenright hive versus a struggling hive. In 2019 and 2020 when this hive was doing well, you can see the mite levels were up between 1-2% during the late summer and fall when I was actively managing mites in the bee yard. My late winter tests showed almost no mites in the hive, which is also normal for a colony that has been mostly broodless for months.
Counting mites after an OAV treatment
But my split in April ultimately doomed the colony. It finally raised a laying queen by late July, but the population had dropped so low they were in danger of being overwhelmed by neighboring bees. I tightened up the entrance to give them a chance, but after getting two consecutive 0% mite tests, I went back into confirm what I already suspected—they had been robbed out, the queen was dead, and only a handful of workers remained. This late in the year, attempting to requeen a colony and get it through the coming winter can be a futile effort, so my solution is usually to cut my losses and do a newspaper combine with a queenright colony. At least this gives the remaining workers a place to contribute and live out their lives in relative comfort.
If the colony hadn’t been decimated by the extended period of queenlessness, the mite levels would’ve spiked in August and September, the same as they did the previous two years. On paper the mite load in this hive looked great this summer. One way to (mis-)interpret the mite tests would be to say “Hey, my bees are mite resistant!” But much like Goldilocks’ porridge, finding too few mites can be as bad—or even worse—than finding too many mites. So outside of Australia and the couple other places on earth still without Varroa destructor, it’s not so bad to find mites in your hives. Just don’t ignore them when you do.