Pest Management

How to Test for Varroa Mites (And What Your Count Actually Means)

By Scout Theory · May 2026 · 10 min read

Varroa destructor is the single greatest threat to managed honey bee colonies worldwide. Every colony has varroa mites. The question is not whether your bees have mites — they do — but how many, and whether the infestation has crossed the threshold where treatment becomes critical.

Testing regularly is the difference between catching a manageable mite load early and losing the colony in October. May is the perfect time to establish your baseline count before summer brood rearing drives mite populations exponential.

Why You Must Test (Not Just Look)

You cannot eyeball a varroa problem. By the time you see mites on adult bees, the infestation is already severe — roughly 5% of adult bees are visibly parasitized when the actual mite population is devastating the brood. Deformed wing virus, parasitic mite syndrome, and colony collapse happen weeks before the visible signs become obvious.

The only reliable way to know your mite load is to count them. The two standard methods — the alcohol wash and the sugar roll — give you a number: mites per 100 bees (also written as mites per 300 bees, since you sample approximately 300 bees at a time).

Method 1: The Alcohol Wash (Most Accurate)

The alcohol wash kills the sample bees but provides the most accurate count. It is the gold standard used by researchers and extension services.

What you need: A varroa mite testing cup (a jar with a mesh lid), rubbing alcohol (70% isopropyl), and a white bowl or tray.

Step 1: Find a frame of open brood (not the frame the queen is on). Hold the jar below the frame and gently shake or brush approximately half a cup of bees into the jar. This equals roughly 300 bees.

Step 2: Add enough rubbing alcohol to cover the bees. Seal the lid.

Step 3: Swirl vigorously for 60 seconds. The alcohol dislodges mites from the bees.

Step 4: Pour the contents through the mesh lid into a white bowl. The mites — small, dark brown, oval — will be visible against the white surface. Count them.

Step 5: Repeat the pour 2–3 times with fresh alcohol to ensure you have captured all dislodged mites.

Method 2: The Sugar Roll (Non‑Lethal)

The sugar roll uses powdered sugar to dislodge mites without killing the bees. It is slightly less accurate (it misses some mites that cling tightly) but appeals to beekeepers who do not want to sacrifice 300 bees per test.

Step 1: Collect approximately 300 bees into a jar with a mesh lid, same as above.

Step 2: Add 2 tablespoons of powdered sugar through the mesh lid. Roll and shake the jar for 2 minutes. The sugar coats the bees and causes mites to lose their grip.

Step 3: Invert the jar over a white bowl or paper plate and shake vigorously. Mites and sugar will fall through the mesh. You can add a small amount of water to dissolve the sugar and make the mites easier to count.

Step 4: Return the sugar-coated bees to the hive. They will be cleaned up by their sisters within minutes.

Reading Your Results: The Treatment Threshold

The widely accepted treatment threshold is 3 mites per 100 bees (or 9 mites per 300 bees) in spring and summer, and 2 mites per 100 bees (6 per 300) in late summer and fall when you need low mite loads going into winter. Many experienced beekeepers treat at even lower thresholds — 2% — to stay ahead of exponential mite growth.

Treatment Options at a Glance

Once you hit the treatment threshold, you have several options. This article focuses on testing — for a deep dive into treatments, see our full guide. Here is a quick overview:

Oxalic acid vaporization is increasingly the treatment of choice for hobby beekeepers. An oxalic acid vaporizer heats oxalic acid crystals into a vapor that fills the hive, killing phoretic mites (those riding on adult bees) without harming the bees. It does not penetrate capped brood cells, so multiple treatments are needed — typically 3 treatments, 5–7 days apart.

Formic acid (Formic Pro) is the only treatment that kills mites inside capped brood cells. It can be applied with supers on, making it useful during the honey flow. However, it can cause queen loss in hot weather, so temperature monitoring is essential.

Synthetic miticides (Apivar/amitraz strips) are effective and easy to use — you insert strips between frames and leave them for 42 days. The downside is that mites can develop resistance over time, so rotating treatments is important.

When to Test: A Schedule

April/May: Baseline test. Establish your starting mite load before summer buildup.

June/July: Mid-season test. Decide whether to treat before or after the honey flow.

August: Critical test. This determines whether your colony will survive winter. Mite loads must be low before your bees raise winter bees in September.

October: Post-treatment verification. Confirm your treatment worked. If counts are still above threshold, treat again immediately.

Testing takes 10 minutes per hive. There is no excuse for skipping it, and no way to manage varroa effectively without data.