Glossary
A naturally occurring organic acid used by beekeepers to treat varroa mite infestations. Oxalic acid kills mites on adult bees through contact without significantly harming the bees when applied correctly. It is approved for use in honey bee colonies by the EPA.
Oxalic acid occurs naturally in many plants (rhubarb, spinach, beet greens) and in honey itself at low concentrations. As a varroa treatment, it exploits a simple biological difference: the acid is toxic to varroa mites at concentrations that adult honey bees tolerate. Applied correctly, it kills 90-95% of phoretic mites (mites riding on adult bees) while causing minimal bee mortality.
Three methods are common. Vaporization (sublimation) heats oxalic acid crystals in a specialized heating wand inserted through the entrance, converting the crystals to a gas that permeates the hive. The vapor condenses on surfaces and bees, contacting mites directly. Dribble application dissolves oxalic acid in sugar syrup and trickles it down the seams between frames directly onto clusters of bees. Cellulose strip methods apply oxalic acid to absorbent strips placed between frames for extended-release treatment.
Vaporization is generally considered the most effective and least disruptive method. It does not require opening the hive, treats the entire interior volume, and introduces no liquid that can chill bees in cool weather.
Oxalic acid kills mites on adult bees but does not penetrate capped brood cells. Since a significant percentage of the mite population is reproducing under capped brood at any given time during the brood-rearing season, the most effective treatment window is during a broodless period. Many beekeepers treat in late fall or early winter when the queen has stopped laying and all brood has emerged, leaving every mite exposed on adult bees.
When used at correct dosages and application methods, oxalic acid is well-tolerated by adult honey bees. Excessive doses or repeated treatments in short intervals can damage bees. Always follow label instructions and EPA-approved application guidelines.
Oxalic acid is naturally present in honey at low levels. Properly applied treatments do not significantly increase oxalic acid concentrations in honey above naturally occurring levels. However, most beekeepers treat during non-harvest periods as a best practice.
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