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Bee-ware of Varroa Mites: Oxalic Acid Hive Treatments

As a part of preparing our hives for the winter, we administer an oxalic acid treatment to each hive to treat for varroa mites. Varroa mites are devastating honeybee parasites if not kept at bay. These mites can evade a single oxalic acid treatment, so they are treated 3 times over the course of 3 weeks.


What are Varroa Mites?

To understand the method of treatment with oxalic acid, it is beneficial to understand the mites we are using it on. As their name suggests, varroa mites are a parasitic mite that live on all life stages of the western honeybee. Being approximately 1.5mm, these mites are actually quite large compared to their hosts, who are 15mm in length. For comparison, that would be like a 5’6” (167cm) human having a 6” (15cm) parasite living on them! These nasty mites feed off their hosts, creating malformations in honeybees who were fed on prior to adulthood. Bees infested with these parasites are known to be smaller in size and contain obvious body malformations. Because these mites create a hole in their hosts, an infected bee will be vulnerable to different infections. Varroa mites can even transmit deadly viruses to a honeybee. Honeybees function as a superorganism; Infection of an individual, therefore, can have a deadly effect on an entire hive. A hive overrun with these pests will not be able to sustain itself for very long before being afflicted by a virus or completely dying.

Varroa mites can enter the hive on an adult honeybee, but they only reproduce in brood cells (where honeybee eggs are laid and larvae develop into adults). They enter the brood cells by falling from infested adult bees. Once the brood cell is capped, the varroa mite will lay many eggs and feed on the larvae as it is developing, but they do not normally kill it. The hatching infected honeybee will bring more mites out into the hive, allowing the cycle to continue. This cycle takes (approximately) 3 weeks, as honeybee eggs take about 3 weeks to develop into adults.


Treating for Varroa with Oxalic Acid

A Warning:

Oxalic acid is not safe for human consumption and should therefore not be used while a hive is supered. Any honey in the hive during an OA treatment should not be harvested for human consumption. Proper equipment should be worn to ensure no beekeepers breath the acid’s vapor, as it can severely damage the lungs over prolonged exposure.


One oxalic acid treatment is not enough to completely rid a hive of its mites. This vapor will only kill the parasitic mites on adult bees. The mites inside brood cells will not be killed and will reinfect the hive as soon as their hosts hatch. To effectively rid a hive entirely from varroa mites, we treat with oxalic acid 3 times over the course of 3 weeks. Our first treatment, in week 1, will kill mites on current adult bees. Since some bees hatching will bring more mites into the hive, the second- and third-week treatments will eliminate the remaining mites as their hosts hatch. Treating with oxalic acid over the length of a honeybee’s journey into adulthood is our attempt at ridding the hive completely of their parasitic varroa mites.

Treating before winter hits is especially important because only strong hives will live through the cold winter months, a time of struggle for any hive. (Conveniently, we have no honey supers on the hives at this time of year). This is why we treat our hives in the fall, right before the weather becomes terribly cold. To administer the oxalic acid into a hive, place a teaspoon of powder on a vaporizer and place the vaporizer under the bottom box of the hive. All entrances and airways in the hive are blocked off at this time (covering with folded blankets/towels does the trick). The vaporizing powder remains in the box for 1 minute and is then removed. The entrances of the hive remain sealed for 10 minutes after vaporizer is removed. After 10 minutes, the entrances of the hive are uncovered! Multiple hives can be treated at once, depending on how many timers you have. Be sure to clean the vaporizer plate between each hive. We repeat this process once a week for three weeks to effectively rid our honeybees of these vicious parasites.


It is important to use caution when uncovering the hives after an oxalic treatment. Covering the hive entrances and flooding them with a smelly gas can result in very angry bees… But like a child receiving their medicine, it may be painful for the parent (beekeeper) but it is beneficial for the child (hive).

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