What Is Varroa?
Varroa destructor is an external parasitic mite that feeds on honey bees (Apis mellifera) and their brood. Originally a parasite of the Asian honey bee (Apis cerana), it jumped to European honey bees in the mid-20th century, and because A. mellifera never evolved natural defenses against it, Varroa has become devastatingly effective.
Left unmanaged, Varroa mites will typically destroy a colony within 2–3 years of infestation — and in some cases much faster. Understanding this pest is non-negotiable for any beekeeper.
What Varroa Does to Bees
Varroa causes harm in two interconnected ways:
- Direct feeding: Mites feed on the fat body (not blood as previously thought) of developing and adult bees, weakening their immune function, shortening lifespan, and reducing body weight.
- Virus transmission: Varroa is the primary vector for a range of bee viruses, most notably Deformed Wing Virus (DWV), which causes bees to emerge with crumpled wings and an inability to fly. A heavy Varroa load amplifies viral levels throughout the entire colony.
How to Monitor Varroa Levels
You cannot manage what you don't measure. Regular monitoring tells you when — and whether — treatment is necessary.
Alcohol Wash (Most Accurate)
- Collect approximately 300 adult bees (roughly ½ cup) from a brood frame — do not use the queen.
- Place them in a jar with isopropyl alcohol (70%) or windshield washer fluid.
- Shake vigorously for 60 seconds to dislodge mites.
- Pour the liquid through a fine mesh strainer and count the mites.
- Divide mite count by 3 to get mites per 100 bees.
Sugar Roll (Bee-Friendly Alternative)
Same process but using powdered sugar instead of alcohol. Slightly less accurate but the bees can be returned to the hive afterward.
Treatment Thresholds
| Season | Treatment Threshold |
|---|---|
| Spring / Summer (brood present) | ≥ 2 mites per 100 bees |
| Autumn (preparing for winter) | ≥ 1 mite per 100 bees |
Treatment Options
There is no single "best" treatment — the right choice depends on your climate, the time of year, whether honey supers are on, and your philosophy toward chemical use.
Organic / Soft Chemical Treatments
- Oxalic Acid (OA): Highly effective when there is no capped brood. Applied as a dribble, vapor, or extended-release strip. Low toxicity to bees.
- Formic Acid (MAQS / Formic Pro): Penetrates capped cells — one of the few treatments effective against mites in brood. Temperature-sensitive; follow label directions carefully.
- Thymol (Apilife VAR, Apiguard): A natural compound derived from thyme. Effective in warmer temperatures. Has a strong odor that can disrupt bees temporarily.
Synthetic Treatments
- Amitraz (Apivar): Plastic strips hung in the brood nest for 6–8 weeks. Very effective but resistance has been documented in some populations. Do not use with honey supers on.
- Tau-Fluvalinate (Apistan) / Coumaphos (CheckMite+): Older synthetic treatments with widespread documented resistance — less commonly recommended today.
Integrated Pest Management (IPM) Approach
Experienced beekeepers don't rely on a single tool. A good IPM strategy combines:
- Regular monitoring (at least once per month in active season)
- Brood breaks — removing the queen briefly so all cells are open when OA is applied
- Drone comb removal — Varroa preferentially reproduces in drone brood; removing capped drone comb takes mites with it
- Rotating treatment chemistries to avoid resistance build-up
- Selecting for hygienic behavior — bees that detect and remove mite-infested brood are naturally more resistant
Never assume a colony is mite-free. Monitor, act at threshold, and keep records. Consistent Varroa management is the single highest-impact thing a beekeeper can do to protect their bees.