Beekeeper’s Guide for Varroa Mite Treatment with Oxalic Acid

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Varroa Destructor mites pose a very great threat to beekeeping, affecting both hobbyist and commercial beekeepers. For years, research has been focused on fighting this honey bee pest but it continues being a problem. One of the most effective compounds used today to control Varroa mite populations in honey bee colonies is oxalic acid. It is a natural compound found in many plants. This guide takes a detailed look at Varroa mite treatment with oxalic acid in both commercial and backyard settings. It also explores the application of oxalic acid in beehives among other useful information for both beginner and pro beekeepers.

Methods of Applying Oxalic Acid

Varroa mite treatment with oxalic acid can be done through a number of application methods. The most popular are trickling, using acid vapor and fogging. While each of these methods has its positives and negatives, trickling presents severe negative effects on bees and the general well-being of the honey bee colony. With trickling, bees ingest more oxalic acid and may suffer ill health. The brooding of bee colonies is also affected when they ingest oxalic acid used for Varroa mite treatment. For these reasons, we will mainly discuss Varroa mite treatment with oxalic acid in the form of vapor and fog.

When using a vaporizer or fogger, the ambient temperature of the device must be between 315 °F (157 °C) and 370 °F (189 °C). At 315 °F, oxalic acid will start to sublime into a vapor. However, beyond 370 °F, it will start to decompose into formic acid and carbon monoxide.

Oxalic Acid Vaporizing for Varroa Mites

Varroa Mite Treatment with Oxalic Acid - Varomorus Durable Oxalic Acid 12V Vaporizer
An example of an oxalic acid vaporizer – the Varomorus Durable Oxalic Acid 12V Vaporizer

Vapor is an effective method of deploying oxalic acid into the beehive. It puts to use the physical properties of oxalic acid by applying heat to sublimate it. Special equipment referred to as vaporizers are required for this. An oxalic acid vaporizer is any beekeeping equipment that you use to heat oxalic acid until it sublimes inside a beehive. Vaporizers are powered using electricity. They run on both DC and AC types of power depending on the manufacturer.

Varying technologies are deployed in the oxalic acid vaporizers. The most popular is the glow plug oxalic acid vaporizer. It is easy to use, has low maintenance costs and can have the glow plug easily replaced in case it is not working. You can even make your own oxalic acid vaporizer if you are a DIY geek! Vaporizers that embed heating coils and other heat production methods in their acid pans are more difficult to repair once they break down.

Things to note:

  • An oxalic acid vaporizer has a handle, a rod, and an acid pan.
  • All vaporizers have leads running from the vaporizer to the power source you will be using.
  • For vaporizers that run on AC power, you need to be near a mains power outlet or have an inverter with you.
  • Those that run on DC power work with most 12V batteries as long as they are in good condition and well charged.

How Does Oxalic Acid Vapor Work?

Oxalic acid vapor is released into the beehive and spreads to all boxes inside it. It then cools down and remains attached to the surfaces of the hive. Mites come into contact with these surfaces as they move around the hive. The mites that have found their way onto the backs of bees also rub against the oxalic acid-coated hive surfaces as the bees move about. This way, mites suffer the effects of coming into contact with oxalic acid.

Using oxalic acid vapor generally results in a high death rate of mites within the first 2 days of application. After that, the numbers of dead mites collected in experiments and studies drop sharply. This may be due to reduced efficiency of the oxalic vapor and an already reduced mite population that leaves fewer mites available to die.

How Quickly does Oxalic Acid Vapor Lose its Effectiveness?

It is important that beekeepers note that oxalic acid from vaporization and fogging remains in the hive in doses that are high enough to kill mites for up to 3 days. After that, natural loss of strength makes the oxalic acid ineffective against mites. It is why a repeat treatment is required after a set period of weeks. This is very well detailed in another section of this article that delves into oxalic acid treatment schedule for beekeepers.

Oxalic acid vapor treatment for Varroa mites places you in close proximity to bee colonies. It specifically requires you to approach the hives in your apiary from the front. This may lead to bees getting aggressive. You must wear protective clothing when carrying out oxalic acid vaporization. A beekeeping suit with veil, gloves and sting-proof footwear are the basic minimum of protective wear you should have. Additionally, you should have a smoker, and plugs to seal beehive entrances and exits.

Things to note:

  • Professional beekeepers have a checklist of items they need for beehive inspections and other hive maintenance activities.
  • Such a checklist for oxalic acid vaporization is very useful to help you bring everything you need, carry out the activity in an efficient and effective manner, and finish the activity on time.


Oxalic Acid Fogging for Varroa Mites

Varroa Mite Treatment with Oxalic Acid - Varomorus Propane Insect Fogger
An example of an oxalic acid fogger – Varomorus Propane Insect Fogger

Fogging is the second method of applying Varroa mite treatment with oxalic acid. Fogging with oxalic acid delivers a large amount in a single application. It is quite fast and allows beekeepers to move from one hive to the next in rapid succession.

The main equipment needed in oxalic acid fogging is of course a fogger. This is a high-temperature device that achieves very rapid sublimation of oxalic acid. Foggers often require the use of oxalic acid in liquid form. Some foggers may take crystals of oxalic acid, but this has some downsides to it.

Things to note:

  • Due to the high temperature that oxalic acid foggers achieve and maintain, you should be very cautious about suffering burns when working with a fogger.
  • Oxalic acid fogging gives a good distribution of the miticide in the hive.
  • Once the hot fog cools down, it leaves the acid on the hive’s interior surfaces.

Beehive structure is a major consideration in fogging. Different foggers have different shapes and sizes of fog delivery nozzles. Small round fog outlets require you to drill a hole in the back of your beehive. The hole is plugged shut when not in use. For oxalic acid foggers with wide nozzles, the beehive entrance is the most suitable point of fog delivery. A few puffs of smoke may be blown into the hive if you will be introducing oxalic acid through the main entrance. Smoke renders bees a little inactive.

Best Time for Oxalic Acid Fogging

If you do not want to inconvenience the bees too much, then you should time your oxalic acid treatment. The evenings when bees are less active are well suited. You will have less activity at the entrance, and all the bees will be in the hive. Beehive management practices do not often go down well when done in the middle of the day when bees are very active.


Creating an Oxalic Acid Treatment Schedule

Varroa Mite Treatment with Oxalic Acid

Varroa mite treatment with oxalic acid requires beekeepers to follow a strict schedule. The proper treatment schedule gives you high effectiveness in your treatment. If you do not follow the schedule, you will not achieve the best result from your use of oxalic acid to treat mites.

What Factors Influence an Oxalic Acid Treatment Schedule?

A number of factors influence the oxalic acid treatment schedule that respective beekeepers should follow. These factors are based on the properties of oxalic acid and the behavioral characteristics of Varroa mites. First is that mites stay in brood cells and emerge together with bees. For worker bees, the period they stay in their brood cells is 11 days. Drones stay in their brood cells for 14 days. This time-frame of brooding is what determines the length of oxalic acid treatment period.

The second important behavioral characteristic of mites is their phoretic time. This is the time they are active and moving around the hive after they emerge from honey bee brood cells. Mites show phoresis for 5 to 11 days before they start entering cells to lay eggs.

The last factor influencing your oxalic acid treatment schedule is the oxalic acid itself. It is not fat soluble, so it does not get absorbed into beeswax. As a result, oxalic acid does not affect mites that are in cells. It is especially useless against mites in capped cells but may have some effectiveness against mites in uncapped cells. The mites must be moving around in the hive, or in uncapped cells if you hope to kill them using oxalic acid.

Things to note:

  • A single application of oxalic acid will, therefore, kill the phoretic mites in the hive but leave mites in cells unaffected.
  • Considering the effective time-frame for oxalic acid, an application keeps killing mites for up to 3 days.
  • After that, the oxalic acid is not effective against mites.

Is one Varroa Mite Treatment with Oxalic Acid enough?

The total effect of a single oxalic acid application by fogging or vaporization is killing phoretic mites, and the mites that emerge from cells in the next 2 days. Due to this fact, you should repeat treatment after the 3 days are past. Beekeepers have repeat treatments between 5 and 7 days.

How many times should Varroa Mite Treatment with Oxalic Acid be done?

Even after your second treatment, there might be mites that you will still not have touched, there are the mites that have still not hatched. Considering that some mites will remain in brood cells for 14 days, you should continue treatments for not less than 14 days. This means that you should have 3 treatments if at an interval of 5 days, and 2 treatments if your interval is 7 days. To be on the safe side, you should add one last treatment to capture any mites that may be still in the hive. Some beekeepers using a 7-day interval between treatments carry out 4 treatments in total. The additional treatment is purely for precautionary reasons.

Modified Varroa Mite Treatment with Oxalic Acid Schedule

Beekeepers have found various ways to modify their oxalic acid treatment schedules. A popular and effective method is queen caging for 21 days before treatment for Varroa mites using oxalic acid. Caging the queen for 21 days prevents her from laying eggs in the hive. There will be no brood by the time you apply oxalic acid in the hive. In this case, two treatments that are not too widely spaced apart give you a very high effectiveness rate. The single biggest challenge with this practice of queen caging is identifying the queen and caging her properly and securely.

Oxalic acid is naturally present in honey. It may also be found in other areas of the hive in varying concentrations. After vaporization or fogging with oxalic acid, the levels of the acid present in the hive undergo a sharp rise. This spike is maintained for a short time and then the levels fall back down to their normal levels.

Timing Your Oxalic Acid Treatment

Timing your oxalic acid treatment is very important. Of course, heavy mite infestations demand immediate action. In less severe Varroa mite infestations, you could delay the treatment for when the hive has less brood within it. This is usually in mid and late winter that falls in the months of December and January in the northern hemisphere. Time your Varroa mite treatment with oxalic acid for this time and you will need fewer treatments.

In addition to vaporization and fogging, we have seen that trickling is another method of oxalic acid application used by some beekeepers. Trickling follows a different schedule of application. It should, however, be noted that trickling leads to ingestion of oxalic acid by bees. At the same time, trickling has a slow release of oxalic acid over a long period of time.


Oxalic Acid Bees Recipe

Varroa Mite Treatment with Oxalic Acid
Oxalic acid dihydrate

Beekeepers must follow very specific oxalic acid bees recipes when treating hives. Deviating from these recipes leads to either application of excess or too little oxalic acid. If you over-apply oxalic acid, it leads to undesired effects on your honey bee colonies. Under-application will undoubtedly lead to reduced effectiveness of the oxalic acid application. In severe under-application, the mites you hoped to kill will not die and you will have wasted time and oxalic acid among other resources. You will then be forced to repeat the treatment, leading to further losses on the part of the beekeeper.

Oxalic acid bees recipes vary depending on the method of application you choose to use. Vaporizers and foggers require little mixing of oxalic acid. Very accurate measurement of the oxalic acid by weight is however required. For trickling oxalic acid treatment, there are a number of recipes that differ based on additives and the purity of your oxalic acid.

Recipe for Fogging

Fogging with oxalic acid is done using a mixture of ethyl alcohol and oxalic acid. 25 grams of oxalic acid powder or crystals are added to 100ml of ethyl alcohol. Stir the mixture until the oxalic acid completely dissolves. This is enough to treat between 30 and 50 hives depending on the severity of Varroa mite infestation.

Recipe for Vaporization

For vaporization, a standard rate of 1 gram of oxalic crystals or powder per beehive box is enough. In oxalic acid vaporization, care must be taken to vaporize all the oxalic acid in the vaporization pan. If you do not allow enough time for complete vaporization, you end up under-applying the oxalic acid.

Recipe for Trickling

Trickling oxalic acid in beehives has more than one recipe. This is because beekeepers use different additives to oxalic acid, and employ different dispersal methods. Generally, absorbent cloth and paper is used to trickle oxalic acid in beehives. The common items used are paper towels and light cloth towels. They release the oxalic acid in small doses into the hive when bees come into contact with them. They can be placed in the hive as large blocks or in strips spread out through the hive. Bees may remove the dispersal material from the hive. If they do not, you must remember to do so after the appropriate time has passed.

The standard recipe for trickling oxalic acid into beehives for Varroa mite treatment is 7.5 grams of oxalic acid in 100ml of water. 100 grams of sugar is then added to this solution. White granulated sugar is best for use.

  • The final concentration of oxalic acid achieved using this recipe is 3.2%.
  • A small digital scale is great for measuring out the different weights of ingredients needed.
  • This oxalic acid bees recipe gives you a medium concentration solution.

Can I make Stronger or Weaker Oxalic Acid Mixtures?

You can make a weaker yet still effective solution by using only 6 grams of oxalic acid while keeping the proportions of sugar and water constant. For a stronger solution, keep the ratio of water and sugar the same, but use 10 grams of oxalic acid. Beekeepers treating more hives should prepare more solution but maintain the proportions of water, oxalic acid and sugar.

  • It is important to note that this recipe for trickling is for oxalic acid from wood bleach.
  • If you are using anhydrous oxalic acid used in laboratories, use a tenth of the oxalic acid; 0.75 grams for a medium strength solution, 0.6 grams for a weak solution and 1 gram for a strong solution.

Oxalic acid reacts with calcium in water and loses its strength. If your water has high calcium levels, consider using distilled water in your oxalic acid bees recipe. To know if your water will present problems, heat some of it in a glass container and add a teaspoon of oxalic acid and stir it well. High calcium content in water causes the water to turn cloudy white when oxalic acid is added.

How to Store Unused Oxalic Acid Mixture?

Oxalic acid solutions can be stored for some time. While it is important to prepare the amount of solution that you will use up, it is sometimes inevitable that some remains. Store the excess solution in cold conditions, preferably in your fridge.

  • The container must be very clearly labeled because oxalic acid is very toxic to humans.
  • Leave no chance that children may reach the container and open it!
  • Storing oxalic acid solutions at ambient temperatures leads to discoloration of the solution, loss of effectiveness and build up of chemicals that are toxic to humans and bees in the solution.

A temperature of 4 0C (39.2 0F) is best for storing oxalic acid solutions. Use up stored solutions as soon as possible.

Purchasing Oxalic Acid


How to Mix Oxalic Acid for Fogger

Varroa Mite Treatment with Oxalic Acid
Oxalic acid dihydrate

In areas where oxalic acid is approved for use to treat beehives for Varroa mites, the approved method is to use the it in its powder or crystal form. The structure of foggers makes it sometimes necessary to dissolve oxalic acid into a liquid. The liquid is then used in small quantities in the fogger.

Beekeepers using oxalic acid foggers to apply it in solution for Varroa mite control must mix the acid properly. Water, ethyl alcohol or mineral oil may be added to oxalic acid during treatment. Improper mixing results into the application of too much oxalic acid, or too little. Excessive application of the mite treatment method is injurious to bees. Applying too little oxalic acid leads to lowered effectiveness in causing Varroa mites’ fall and subsequent death.

Things to note:

  • For best results when you have to mix oxalic acid for the fogger, use water.
  • Clean water is a great agent to get oxalic acid into the hive and deposit it on beehive surfaces. Water is also easy to remove from the hive.
  • Bees exposed to water do not show any negative effects on their health. This cannot be said of other substances that beekeepers may consider using alongside oxalic acid.

Oxalic Acid and Water Mixture

To make a mixture of oxalic acid and water, add 25 grams of oxalic acid to 100ml of water. Make as much of the mixture as you will need for treatment of all your hives. On average, 100ml of the mixture should see you through 30-50 beehives. If you cannot do that, you will be over-applying oxalic acid. Severely infested beehives may be fogged with slightly more oxalic acid than less severely infested hives.

Water boils at 100 0C (212 0F) and turns into gaseous water vapor. Oxalic acid foggers achieve a temperature of 230 0C (446 0F) at the start of fogging. The temperature rarely drops below 150 0C (302 0F). This means that all the water that goes into the fogger during treatment is instantly turned into its gaseous form. It leaves the fogger together with the sublimed oxalic acid. Once in the hive, it cools down and helps oxalic acid attach to beehive surfaces.

Oxalic Acid and Ethyl Alcohol Mixture

A mixture of ethyl alcohol and oxalic acid is often used in fogging. It is the second best choice of solute when mixing oxalic acid for a fogger. The oxalic acid used is often obtained in powder form as wood bleach. 25 grams of this substance is added to 100 ml of ethyl alcohol. Make sure to stir the mixture properly. A few drops are used at a time. 100 ml of ethyl alcohol and oxalic acid mixture is enough for treatment of between 30 and 50 beehives.

Mineral Oil and Oxalic Acid Mixture

Care must be taken before adding mineral oil to oxalic acid for use in beehive fogging. This is due to the properties of mineral oil which render it not able to dissolve oxalic acid. The result is that mineral oil being fogged is in its pure form. Oil is a hydrocarbon and when heated to high temperatures it becomes very flammable. There is a very high likelihood that the mineral oil will burst into flames when run through a fogger. Beekeepers should take a lot of care not to throw a burst of flames into their hives. Bees get singed and the hive may catch fire.

Important Points to note about Oxalic Acid Mixtures

  • Mixtures of oxalic acid may be stored for some time and used in subsequent fogging activities.
  • It is important to note that the acid deteriorates in quality over time. You will note this as discoloration of the mixture.
  • Do not store your oxalic acid mixture in ambient temperatures if you hope to use it later. Keep the mixture refrigerated at 4 0C (39. 0F) or lower.
  • Additionally, make sure to keep the mixture out of reach of children. The container holding your stored oxalic acid mixture must be clearly labeled.


The Oxalic Acid Vaporizer vs Fogger

Varroa Mite Treatment with Oxalic Acid
Honeybee coated with oxalate crystals

The choice between oxalic acid vaporizer and fogger can be difficult for beekeepers to make. Both are effective in treating beehives with oxalic acid. There are however significant differences between the two oxalic acid application equipment. Let us look at the differences between the two, their advantages and disadvantages.

An oxalic acid vaporizer uses DC power to heat oxalic acid to sublimate it. A vaporizer is shaped like a rod with an acid pan at one end. It goes into the hive bottom.

A fogger uses various heating methods. One design of fogger uses AC electricity to heat oxalic acid and the other uses gas – usually propane. A fogger does not enter the hive. It delivers oxalic acid into a beehive through a hole drilled into the back of the hive.

Some foggers have digital temperature readouts. These allow you to know once the oxalic acid sublimation temperature has been reached. They are more efficient and easy to use than those without the readout.

Advantages of Vaporizer over Fogger

  1. Oxalic acid vaporizers are easy to use. They are simple and go into the hive easily. Foggers need some getting-used-to before beekeepers are comfortable working with them. Beginner beekeepers may find it tough figuring out how to set up everything and get it working. A vaporizer is on the other hand quite straightforward.
  2. When you have a few beehives only, a vaporizer is the wise economic choice to make. A vaporizer is generally way cheaper than a fogger. This difference in price is largely caused by the difference in technologies used.
  3. Easy to maintain and repair if it breaks down. Vaporizers that utilize glow plugs as their heating method are especially easy to fix if things go wrong. A fogger has a collection of different technologies and parts. Some of the parts will need you to visit a specialist if something goes wrong with them.

Advantages of Fogger over Vaporizer

  1. A fogger delivers a large dose of oxalic acid is a few bursts.
  2. Does not put hot parts in the beehive. This greatly reduces the risk of fire catching in the beehive. A vaporizer has the acid pan in the hive and may cause a fire break out if there is wax or other flammable material at the bottom of the hive.
  3. It allows you to move from one hive to the next quickly. A fogger does not need cooling after every hive treatment. This is one of the biggest advantages a fogger has over a vaporizer.
  4. By approaching the hive from the back, a fogger puts you in a position where you cause less obstruction to bees and contributes to less aggravation of the bees.

Equipment Needed

When it comes to the equipment needed to operate a fogger or a vaporizer, they both score equally. The average vaporizer needs you to bring a car battery or other 12-volt DC power source with you. Some oxalic acid foggers running on AC power need an inverter in addition to the battery, or a generator nearby. This is all if you are not near a source of mains electricity. Foggers that run on propane need you to bring a propane tank with you.

From the advantages that the respective oxalic acid application equipment has over the other, a fogger wins over the vaporizer. Beekeepers who wish to get through the job quickly and with minimal disturbance to bees should go for the fogger. It is great for treating many hives, and still works for the beekeeper with a single hive. If you are going to be controlling mites using oxalic acid, why not just go for the fogger? Well ultimately it depends – on your needs, your location and the availability of the equipment. Depending on where you are, it may be easier to get a vaporizer over a fogger. And furthermore, if you don’t have plenty beehives, then it may not be necessary to get a fogger.


Oxalic Acid and Honey Supers

Varroa Mite Treatment with Oxalic Acid

Varroa mites present in a beehive increase in number when brood is present. This is usually in spring and summer. Unfortunately, it is also the time that bees are making a lot of honey. Winter sees the number of bee brood greatly diminished. Oxalic acid treatment for Varroa mites is best done in winter when there is little or no brood. In winter, there is little honey present in the hive and it is used up by bees as their food source.

There are concerns about using oxalic acid with beehive honey super boxes present. Oxalic acid is not soluble in lipids. This makes it very difficult for oxalic acid to pass honeycomb and get into honey. Additionally, oxalic acid dissipates quickly from the hive to acceptable concentrations. As a result, some beekeepers may treat their hives with oxalic acid while having honey supers on the hive, though we would not recommend this. This is mostly done when the circumstances are dire and the Varroa mite population threatens to overwhelm your honey bee colony.

How Safe is Honey after Oxalic Acid Treatment?

Safe honey for human consumption must be free from chemicals. Oxalic acid is considered a natural compound for Varroa mite treatment. It is found in plants, in your beehives and even in honey in small quantities. To address any honey safety concerns that you may have, you could remove honey supers from the hive when treating with oxalic acid. To remove honey supers or not is a decision that individual beekeepers make. If you remove honey super boxes, leave them off for 14 days. Oxalic acid treatments has not yet been approved for use with honey supers in most jurisdictions.

What if I leave my Honey Supers on?

If you choose to leave your honey super boxes on the beehive during Varroa mite treatment with oxalic acid, do not harvest the honey for at least 14 days after treatment. The oxalic acid will dissipate from the hive to normal levels in the 2 weeks. You may then proceed with harvesting your honey.

Takeaway Points about Oxalic Acid and Honey

  • Oxalic acid does not get into honey easily. The wax in honeycomb cells makes sure of this.
  • Honey naturally has some amount of oxalic acid in it.
  • You may remove honey super boxes for 14 days after treatment with oxalic acid.
  • If you leave your beehive super boxes on the hive during treatment, do not harvest the honey for 14 days.


Safety Precautions for both Beekeeper and Bees

Varroa Mite Treatment with Oxalic Acid

Oxalic acid is a very toxic substance. It is an organic acid but very corrosive. Safety precautions should be taken to prevent beekeepers and bees from getting harmed. The aim of Varroa mite treatment with oxalic acid is to kill the mites only. You must take safety precautions for both beekeepers and bees when handling and using oxalic acid.  The lethal dose for adult humans is 15-30 grams of oxalic acid via ingestion. If any of the acid gets spilled, clean it up immediately. Due to its toxicity and lethal effects on humans, do not use oxalic acid in enclosed spaces.

Oxalic Acid Effects on Humans

If oxalic acid comes into contact with your skin or eyes, burns and blisters will form. Ingestion is worse. It leads to injury to the mouth, throat, stomach and intestines. Additionally, oxalic acid will form kidney stones when ingested. The kidney stones may ultimately lead to kidney failure. This is the main effect that gives oxalic acid its lethal properties when swallowed. In treating beehives with oxalic acid, make sure it will not come into contact with your skin or eyes. Do not breathe in the fumes of oxalic acid either, or swallow any oxalic acid.

Beekeepers are best protected from the effects of oxalic acid by wearing protective suits. The average beekeeping suit is often adequate as a protective measure for your body. However, ventilated beekeeping suits are not very suitable for use when you are working with oxalic acid. Strong waterproof gloves must be worn too. To prevent inhalation of toxic oxalic acid fumes, wear a gas mask. The gas mask must be thick enough to filter out all oxalic acid. Respirators with particulate filters are especially suited for use when handling this corrosive acid.

Things to note:

  • Safety goggles will keep your eyes safe and must be worn at all times.
  • After you are done treating your hives with oxalic acid, remove the protective clothing and equipment you were wearing and clean them with ample amounts of water.
  • You should also take a bath soon after.

First Aid for Oxalic Acid Poisoning

If you come into contact with oxalic acid during beehive treatment, douse the area with a lot of water. Take off any contaminated clothing immediately too. Having some baking soda dissolved in water nearby is useful. Baking soda neutralizes the oxalic acid very fast. If you ingest it, take milk immediately or large amounts of water. Do not induce vomiting after swallowing oxalic acid. When oxalic acid is inhaled, move to an area where there is fresh air immediately. Do not attempt mouth to mouth resuscitation.

These are however only first aid measures. You should seek medical attention immediately and inform the healthcare provider that you have oxalic acid poisoning. Your health prognosis after coming into contact or swallowing oxalic acid depends on:

  • How much acid you swallowed
  • The concentration of the acid
  • Length of time that the acid was in contact with your skin or eyes
  • How quickly you received medical assistance

Oxalic acid must be stored in clearly labeled containers and kept out of children’s reach. To store oxalic acid, do not use containers or utensils that are used for food preparation.

Safety Precautions for Bees

While oxalic acid is safe for use in beehives, it has the ability to harm bees in high concentrations. Bees ingesting oxalic acid show side effects at lower concentrations of the acid than in bees that only come into contact with the acid on their skin. Even when bees do not die immediately, a high concentration of oxalic acid shortens the lifespan of individual bees. Oxalic acid affects bees’ response to stimuli in their environment. It also affects their senses and ability to detect pollen and nectar.

Things to note:

  • Bees that have been poisoned by oxalic acid cannot perform hive maintenance activities properly. Even with sugar syrup feeding, the bees will not thrive.
  • Care must therefore be taken when preparing trickling solutions of oxalic acid for Varroa mite treatment.
  • Vaporization and fogging must also be done with just the right amount of oxalic acid.



Oxalic acid is an effective miticide that is found in nature. While it is injurious to humans in large quantities, it rarely remains in honey or beeswax in large amounts. This allows you to produce high-quality contaminant-free honey. Nonetheless, it is okay to play safe and remove honey super boxes from your beehives when treating with oxalic acid.

Once it comes into contact with mites, oxalic acid rapidly leads to loss of viability in the mite. Mites may also ingest oxalic acid without loss in its potency. Vaporization and fogging remain the best methods by which to apply oxalic acid in beehives. The two methods allow easy, effective and efficient Varroa mite treatment. Keep your apiary free of Varroa Destructor mites using this method of Varroa mite control.


Have you used oxalic acid as a Varroa mite treatment in your beehives? Leave a comment below and let us know what your experience was like.

About Michael Simmonds

Michael Simmonds is a beekeeper from the United States, with over 20 years of experience in the field. He developed a passion for beekeeping at a young age and started his own apiary when he was just 15 years old. Over the years, he honed his skills and gained extensive knowledge about honeybee biology and behavior. Michael's passion for bees led him to start his own business, where he provided honeybee colonies to farmers and gardeners to help pollinate their crops. His business quickly gained popularity and recognition, and he became known for his expertise in honeybee health and management. He was also sought after for his knowledge about the art of extracting honey, and many aspiring beekeepers sought his guidance on how to get started. Aside from his beekeeping business, Michael is also a dedicated advocate for honeybee conservation. He is passionate about educating the public about the importance of honeybees and the role they play in our ecosystem. He also works with local organizations to help preserve wild honeybee populations and protect their habitats. Michael's passion for bees and dedication to his work have made him one of the most respected beekeepers in the country. He continues to work with bees and share his knowledge with others, hoping to inspire a new generation of beekeepers and to help protect these amazing insects for generations to come.
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3 years ago

hi. can i use oxalic acid all the time to kill varroa??
.why you dont talk about formic it bad??

Herbert Mueller
Herbert Mueller
3 years ago

Are you sure about the 2.5 grams of Oxalic acid per 100 ml solvent? Every other website I’ve seen says 25 grams / 100 ml, so 10 times the concentration you state.

3 years ago

When I vaporize OA there is a bunch of powder laying beside it at the end. Adding a few drops of water to the powder before vaporizing seemed to help.

john payne
john payne
3 years ago

i live in New Hampshire, and will start my first treatment this weekend it will be warmer that usual,around 44 but is i maintain a 5 day 3 treatment it will be back to the upper 20’s any problem with temps then

Mack Tyner
Mack Tyner
3 years ago
Reply to  john payne

Here in Florida, I vaporize oxalic early in the morning, before the bees fly. We use screened bottom boards to allow mites to fall out of the hive if they lose their footing. So the oxalic can be placed on a metal sheet below the hive, and the fumes just go up into the hive thru the screen. You will see it gently wafting out of the entrance and the ventilation holes in the back of the hives. A few bees will come as well, due to the irritation of the fume. Cool mornings (35-50 F) ensure that the fume… Read more »

2 years ago

Most fogger mixes I have seen use Ethyl alcohol or everclear. I like the idea of just water and OA. What are the cons of water vs alcohol for fogger use. Thanks.

Michael E Cooper
Michael E Cooper
2 years ago

Are their temperatures above which and below which a Vaporizor should not be used?

2 years ago

Hi. I have used a vaporizer twice this year. The first time I used it I did 4 treatments every 5 days. I just finished 6 treatments every 4 days. Both times I did not get a reduction in my mite counts. The counts went up. I am in Georgia. Can the high humidity be affecting the treatments?

1 year ago

How do you store honey supers when removed for oxalic treatment if your not ready to process honey yet ?

1 year ago
Reply to  John

Thank you for your information, could you cover brood boxes with plastic cover then put suppers back on while treating if you don’t have the freezer space? This is my first year bee keeping. The hives’shave been doing great hate to mess up

1 year ago

Thank you for your time and knowledge very helpful

How to Remove Dark Stain From Wood | SawsHub
1 year ago

[…] acid dihydrate, and is composed of tiny crystals. It is odorless and easily dissolvable in water. The vapor form of oxalic acid is used to protect beehives from certain types of mites, while the liquid created when crystals and water combine  is commonly referred to as ‘wood […]

1 year ago

I have a Varomorus Turbo flogger. I have used 25 grams ( about 3 tbs) of powdered OA in 91% isopropyl alcohol, vodka (40%) or Everclear 95%. I heat 100 milliliter of which ever solution I have used until the OA dissolves and will pass through a coffee filter. But regardless of the solution in which I dissolve it, the OA will separate out and settle to the bottom within a very short time (before my hives are treated). The OA that has settled out plugs the pump and therefore the flogger will no longer work, and even if it… Read more »

8 months ago

Hi, I’m on my 3rd treatment of OA vapor tonight and will most like do a 4th in 5-6 days. After this cycle, how long should I wait to do another cycle, if needed? I’m debating to alternate with other treatment methods like FormicPro or Apiguard/var, but the OA really seems to do the job so will just stick with OA method if ok to do.

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[…] a few products on this list make use of a substance called oxalic acid. Now, you might be wondering what that is exactly, and in this section, we’re going to talk a […]

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[…] acid dihydrate, and is composed of tiny crystals. It is odorless and easily dissolvable in water. The vapor form of oxalic acid is used to protect beehives from certain types of mites, while the liquid created when crystals and water combine  is commonly referred to as ‘wood […]

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