Summer Varroa Monitoring: Your July Mite Check Decides the Winter
A practical Nordic guide to July varroa monitoring — why mites peak late summer and damage winter bees, how to test with alcohol wash, sugar roll and natural drop, what thresholds mean, and how the count sets up your August treatment.
By July the beekeeping year at our Svinninge apiary, just north of Stockholm at roughly 59° north, looks calm on the surface — supers filling, foragers streaming, colonies at their peak. But underneath the cappings, something is quietly building that will decide whether these colonies see spring. This is the month to stop guessing about varroa and start counting.
Why a July Mite Check Matters More Than You Think
Varroa is the single biggest cause of colony death in the Nordic climate, and it rarely kills directly. Instead the mite acts as a syringe, spreading viruses — above all Deformed Wing Virus (DWV) — as it feeds. A colony that looks strong in July can be gone by February, and the reason is almost always mites and the viruses they carry.
The problem is timing. Mite populations grow all summer while there is brood to breed in, roughly doubling every three weeks. Swedish figures put it starkly: a colony can carry something like 100 times more mites in August than it did in March. And the damage lands at the worst possible moment — on the winter bees, the long-lived generation raised in late summer that must survive months of cluster and carry the colony into spring. High DWV levels in November and January are directly linked to shortened winter-bee lifespan and colony loss.
For us here, this is not abstract. COLOSS winter-loss surveys have found Stockholm County — Svinninge included — running higher winter losses than the rest of Sweden (over 20% in some recent years, against under 10% elsewhere), and beekeepers on Värmdö have tied that pattern to deformed wings seen in colonies the previous summer. If you keep bees around Stockholm, a July mite check is arguably the most locally relevant thing you can do all season.
How to Actually Count Your Mites
You cannot judge a colony by eye. Seeing no mites tells you almost nothing — no detection is not the same as no mites — because during the brood season most mites are hidden under cappings. So we sample.
The unit is roughly 300 bees, about half a cup, shaken from a brood-nest frame — and critically, make sure the queen is not on that frame before you scoop. From there, choose your method:
- Alcohol wash — the most accurate. Drop your ~300 bees into alcohol (or a windscreen-washer fluid; dish soap at about a tablespoon per half-gallon of water also works), swirl hard for 30–60 seconds, and count the mites that release. It kills the sample of ~300 bees, but it is harmless to the colony as a whole and gives the truest number.
- Sugar roll — non-lethal, almost as good. Coat the same ~300 bees in powdered sugar, shake the mites out onto white paper, and return the bees unharmed. Slightly less reliable — humidity, nectar and clumping can hide mites — but excellent when you would rather not sacrifice bees.
- Natural drop / sticky board (nedfall). The Swedish first-line standard: a screened bottom board (varroanät) collects mites that fall naturally over several days, giving a mites-per-day figure. No bees are handled at all.
- Drone-brood uncapping. Mites prefer drone cells, so uncapping around 100 drone pupae and inspecting them both measures pressure and, done repeatedly, removes mites.
One honest caveat runs through all the adult-bee tests: when there is a lot of sealed brood, they underestimate, because that is exactly where the mites are hiding.
Reading the Thresholds — and Why There Is No Magic Number
This is where beekeepers get tangled, so let us be careful and honest: thresholds vary between sources, and none is universal.
- The Honey Bee Health Coalition (Tools for Varroa Management) works in mites per 100 bees, which reads directly as a percentage, and a roughly 3% action threshold is commonly cited — worth attributing, not treating as gospel.
- The University of Minnesota Bee Lab now leans more conservative: keep infestation under 1% year-round and treat if you cross 2% (about six mites per 300 bees), lower than the old 3% because virus pressure has risen. As they put it plainly, "recommended thresholds have trended lower… there is no universal standard."
- For Nordic conditions, the Swedish natural-drop guide is the most usable: roughly 1 mite per day in late June corresponds to around 120–130 mites in the colony; up to about 3 per day is still considered winterable, while more than 3 per day means treat as soon as possible (akutbehandla).
A safe way to hold all this in your head: US guidance sits around 2–3 mites per 100 bees, UMN now leans to 2% or under, and Swedish practice watches the natural drop — about one a day in late June points to 120–130 mites, and over three a day says treat now. Check the drop at least twice a season — once in June/July and again in autumn — and let the summer number set the urgency of what comes next.
How July Sets Up the Two-Step Autumn Treatment
The whole point of counting now is that it decides your August plan, and Nordic treatment is a two-step affair.
Step one, after the final harvest (slutskattning) in late July or August, is usually formic acid (myrsyra), which is unusual and valuable because it works through the brood cappings to reach hidden mites. It needs the right weather — apply at roughly +15 to +25°C, never above 25 — or thymol (Apiguard) through August–September above +15°C. Step two is oxalic acid (oxalsyra), applied in the broodless window of late autumn or early winter, once the colony has stopped rearing brood (typically from around October, above 0°C and snow-free). Oxalic only reaches mites riding on adult bees, which is exactly why the colony must be broodless for it to work.
Your July count is the trigger for the urgency and timing of step one. And remember the paperwork: in Sweden beekeepers are legally required to keep a medicines log (läkemedelsjournal) recording treatments including organic acids (Jordbruksverket), and the disease regulation (Bisjukdomsförordningen 1974:212) obliges varroa control. Monitoring is not just good practice; the follow-through is a legal duty.
Where Colony Strength and Nutrition Fit In
There is a real and elegant link here worth knowing. Research overturned the old belief that varroa "drinks bee blood": the mite actually feeds primarily on the fat body (Ramsey, 2019, PNAS) — the very tissue that produces vitellogenin and makes a bee winter-hardy. So the mite attacks the exact organ a colony needs to survive winter, which is why a heavy mite load and a failed overwintering go hand in hand.
Because of that link, colony nutrition genuinely matters. Well-fed bees with good pollen-built vitellogenin reserves are longer-lived and more immune-competent, and a strong colony tolerates and recovers from stress better. Our Dr. Gost pollen cakes, bee vitamins and probiotics are built to support exactly that winter-bee and fat-body pipeline — helping a colony go into autumn well-nourished and resilient. We are honest about what that is: support, not a substitute. Even a strong, well-fed colony gets overwhelmed if the mite and virus load climbs too high. Nutrition helps the survivors survive; it does not replace monitoring and treatment, and it makes no claim to touch a mite. Count first, treat on time, feed well — in that order.
Get your July check done, write the number down, and you will walk into August knowing exactly what your colonies need instead of hoping. From all of us at Buzzin' Bees — happy summer, and steady hands on the sticky board.