The Bee Bench › Varroa Mite Check
You counted the mites. Here's what the number actually means, and whether you're over the line for the time of year.
Take the sample from an open brood frame — that's where the mites are. Shake the bees off the frame into a tub first, then scoop. Make sure the queen isn't in there.
The colony figure counts only the mites riding on adult bees. When there's capped brood, roughly two out of three mites are hidden inside cells where no wash will find them — so the true load is often two to three times this.
| Time of year | Act at | Why |
|---|---|---|
| April–July | 2 per 100 | Brood rearing is in full swing and mites roughly double every month. A low count now is what keeps August manageable. |
| August–October | 3 per 100 | Set higher because brood is shrinking, so more of the mites are riding on bees where a wash finds them, and counts read higher. Not a reason to relax: the bees raised now have to live six months, and mite-damaged winter bees are why colonies die in February. Act the day you cross it. |
| November–March | 2 per 100 | Cornell doesn't publish a winter number, so we use the spring one. With little or no brood every mite is on a bee — the single best time to hit them with oxalic acid. |
Thresholds follow the Cornell Master Beekeeping course's Northeast numbers: act at 2 mites per 100 bees April–July and 3 per 100 August–October. Above them, Cornell finds colonies are likely to die within six months to two years without treatment. Sample every colony you can, not just the ones that look bad — the strongest hive in the yard is often the one robbing out a collapsing one down the road and picking up its mites.