What Are Varroa Mites?
Varroa destructor is an external parasitic mite that feeds on the fat bodies of developing and adult honeybees. Introduced to Western honeybee populations in the 20th century, Varroa has become the single greatest biological threat to managed colonies worldwide. Left untreated, a Varroa infestation will collapse a hive within one to three years.
Why Varroa Is So Dangerous
Varroa mites cause harm in two distinct ways:
- Direct feeding: Mites puncture the cuticle of bees and pupae, weakening them and shortening their lifespan.
- Virus transmission: Varroa acts as a vector for a range of viruses, most notably Deformed Wing Virus (DWV), which causes bees to emerge with shrivelled, useless wings.
A colony with high mite loads will produce bees with reduced immunity, shorter lives, and impaired navigation — a recipe for rapid decline.
How to Monitor Mite Levels
Regular monitoring is the foundation of effective Varroa management. The two most reliable methods are:
1. Alcohol Wash (Sugar Roll)
- Collect approximately 300 bees (roughly half a cup) from a brood frame into a jar.
- Add isopropyl alcohol (or powdered sugar for a non-lethal version) and shake for 60 seconds.
- Pour the liquid through a mesh screen and count the mites.
- Divide mite count by the number of bees to get your infestation rate.
A mite wash result of 3% or higher (3 mites per 100 bees) generally indicates treatment is necessary.
2. Sticky Board Count
Place a sticky board beneath your screened bottom board for 24–48 hours and count the mites that fall. This gives a natural mite drop rate — useful for tracking trends over time, though less precise than a wash.
Treatment Options
| Treatment | Active Ingredient | Best Used | Notes |
|---|---|---|---|
| Oxalic Acid Dribble/Vaporization | Oxalic acid | Broodless period (winter) | Highly effective; approved for use with honey supers in some regions |
| Formic Acid (MAQS / Formic Pro) | Formic acid | Spring/Autumn | Penetrates capped brood; temperature sensitive |
| Amitraz (Apivar strips) | Amitraz | Spring/Autumn | Effective but resistance possible with overuse |
| Thymol (Apiguard / Api Life VAR) | Thymol | Late summer | Temperature dependent; avoid during honey flow |
Integrated Pest Management (IPM)
Rotating between different treatment types is strongly recommended to prevent mite resistance. Combine chemical treatments with cultural controls such as:
- Brood breaks: Temporarily removing the queen to interrupt the brood cycle exposes mites to treatment.
- Drone comb removal: Varroa preferentially infests drone brood; removing capped drone frames reduces mite populations.
- Using resistant stock: Selecting for Varroa Sensitive Hygiene (VSH) or hygienic bee genetics reduces long-term mite pressure.
When to Treat
Treat proactively, not reactively. The best times to apply treatments are late summer after the main honey flow and again in late autumn when brood is minimal. Always follow product label instructions and local regulations.
Final Thoughts
Consistent monitoring — at least every four to six weeks during the active season — is the most important habit a beekeeper can develop. Catching a rising mite load early gives you options. Catching it late often means losing the colony.