Oxalic Acid for Bees

For many beekeepers (myself included) using oxalic acid for bees as a part of varroa control is very beneficial. Varroa mites devastate the health of honey bee colonies resulting in the death of thousands of hives. The beekeeper’s goal is to destroy the mites without harming the bees – a difficult task. In this guide, I share the two most common ways oxalic acid is used by beekeepers.

When I first became a beekeeper, varroa mites were already a part of the beekeeping experience. I struggled to avoid the harsher varroa mite treatments, seeking a natural treatment that would work effectively in hot weather. Oxalic Acid vaporization – while not perfect – has helped make a difference.

Understanding Oxalic Acid and Varroa Mites

Varroa mites (Varroa destructor) are tiny, external parasites that target honey bees. (I think of them in the same terms as fleas feeding on a dog – however it is a bit different).

Mites feed on the fat bodies of both adult bees and developing young. This weakens bee brood and causes overall bad colony health and decline.

The mites you can see on the bees are called “phoretic” mites. But, it is the mated females hidden inside brood cells that are the major threat. They are reproducing.

How Oxalic Acid Affects Varroa Mites

Used correctly, oxalic acid targets the phoretic mites that are attached to adult bees. When oxalic acid is applied to a hive, it comes into contact with the varroa mites. Sharp acid crystals penetrate the mite’s exoskeleton causing damage – dehydration and death.

There is still some debate among researchers over the exact way mites are killed. Whether it is partially through inhalation of the vapor by mites or solely direct contact with spiky dried crystals. But, the benefits are clear:

• kills mites-does little harm to bees
• mites do not become resistant to it – continues to work
• leaves no toxic residue in the hive, honey or beeswax honeycomb.

In the dribble (or trickling) method, the acid is mixed with warm 1:1 sugar water (equal parts of sugar and water). Then, (using a syringe) the mix is applied between the frames in the hive – directly wetting the bees clustered there.

Care must be taken to not use more than a total dose of 50 ml per colony (of course you would adjust for smaller colonies).

Because the dribble method is hard (harsh) on the cuticle (exoskeleton) part of honey bees, it should only be done 2 times a year.

Also, the bees need to be somewhat clustered together between the frames for application. This means that dribbling is best in cooler weather.

In a similar application, spraying bee packages is sometimes employed by those in the bee farm or beekeeping business that sell bees.

The most popular method is – “oxalic acid vaporization“. A small amount of oxalic acid crystals are placed on a special wand.

The wand is inserted into the hive and heated (external power source) to vaporize the crystals. Once the temperature reaches about 314° F, sublimation occurs and the solid crystals become gas.

This vapor disperses through the hive. As the gas vapor cools, small spiky crystals are left behind on the bees, comb and hive walls. Varroa mites exposed to the crystals will die.

With vaporization we are not trying to coat the bees, rather we are injecting the heated vapor into the hive environment.

How to Use Oxalic Acid Vaporization

This is an overview of one way to use an oxalic acid vaporizer. This is my process – always follow directions that come with your equipment and materials.

Choosing a Vaporizer Wand

There are many types of wands available. Some work great but are expensive, some are more affordable and work good and others are pieces of “kaka”.

The wand I currently use is called the Varrox from Oxavap. It has held up for many years and is still working great.

I chose it because I could dip the heated bowl into water to quickly cool it down and move on to the next hive – you can’t always do that with the cheaper products.

And, because I no longer keep a lot of hives – I didn’t think it was smart to buy one of the Cadillac models. The cheaper options can work well too – shop around before deciding. Most will require a power source – electric, battery etc.

4. After inserting the wand bowl (- with crystals) into the hive entrance. I lay an old towel (or similar) across the front of the hive. This temporarily plugs the entrance – keeping foraging bees out and hopefully some vapors in.

You can seal the entrance and any cracks with painters tape or anything that keeps vapor in for a few minutes but a cloth or canvas is quick and easy for me.

When treating the hives in cooler weather – I often am able to stick the wand through the largest opening of the entrance reducer. Less disturbance for the bees. But, when you remove the wand – watch out!

5. Connect vaporizer to power source and set a timer for 2.5 to 3 minutes. The time varies depending on the model vaporizer you have. This will require a bit of testing. Stand upwind from the hive during treatment.

7. After removing the wand, I open up a tiny spot on the toweled front to let some unhappy bees locked out – get back in. Wait an additional 8-10 min before opening all the entrances and beehive ventilation ports.

I too am guilty of getting lazy – but every mite treatment should be followed up with a mite count a couple of weeks later. No method always works. Don’t just treat and forget it – do your counts.

Timing Oxalic Acid Treatments

As for when to perform mite treatments, consider the treatment threshold for bees in your area. This number seems to change a bit as the years go by – it is a good idea to keep in touch with local beekeeping associations.

It doesn’t really matter what time of day you do your oxalic acid treatment. As for best time of year to treat, doing your varroa mite tests or counts is the only way to know if you have a problem.

It is important to note that – oxalic acid vaporization is most effective when there is little or no brood in the hive.

This is not always possible for Southern beekeepers-our colonies may have brood year round. A common treatment plan is:

• late Fall or early Winter
• before honey supers go on the hive in early Spring
• for new hive splits with little capped brood
• mid-late Summer (3 treatments required)

Oxalic Acid Vaporization With Brood

Oxalic acid treatments only kill phoretic mites – the foundress mites found on the adult bees. Oxalic Acid does not kill mites under the cap. This is why the very best time to use OA is when the colony is broodless.

For many Southern beekeepers, finding a natural treatment to use for mite control is very difficult. At the time of year when I really need to treat my colonies, it’s too hot to use the temperature sensitive natural methods.

By the time the daily temps cool down, my colony may already be dead or so infested with mites that it has one foot in the grave.

Three Time Summer Special

To overcome this challenge, I do 3 vaporization treatments that are 4-6 days apart. In this way, as more mites emerge with new bees -most of the mites will be out of a cell and exposed to one of the treatments.

A recent study suggested that this 3 treatment regime is just not enough to kick the mite load down far enough. I respect that but have not found a better alternative.

If you are trying to avoid using the harsher chemicals (Apivar, Apistan etc.) and hot weather prohibits the use of formic acid or thymol – OA is the only thing we have right now.

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