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Varrox Evaporator Instruction Leaflet
as Re-Written by Dave Cushman

Also known as Varrox vaporiser, but this page will only use the term Varrox evaporator.

This Instruction leaflet is written from the point of view of UK beekeepers, using terminology understood in UK, rather than an English translation from another language. I have no connections, with Varrox, BioVet or Thornes, nor do I promote or denigrate the use of this product. You should establish that it's use is legal in your own area or country and take notice of the warnings regarding oxalic acid. If, however, anyone reading this version does not agree with my interpretation of the text on the original leaflet, please get in touch and the text can be changed, because that may help others.

The device itself, consists of a metallic pan surrouded by a heating element, the connections for this element are passed through a rigid portion of handle which has large hexagonal wings to ensure that the pan stays horizontal when inserted into the hive. Connection is made to a battery or other energy source, via a three metre long cable with either battery clips or a car cigarette lighter type plug.

The one at right is the battery clip version.

  Varrox Evaporator with battery clips


facsimile of header from Andermatt leaflet

Varrox evaporator image, similar to leaflet image, source... Richie Moran

General license and distribution:
Andermatt BioVet AG. Stahlem1stten 6,
Phone ++ 41 62 917 51 10
Fax ++41 62 917 5111

Leaflet issue date... March 2002

1. Appliance

The VARROX-evaporator consists of a heater, a metallic support and 3 .m of lead with 2 battery- clips. It has an output or 150 W. The power source can either be a 12v car battery of 40 Ah or more, other type of accumulator, or a car cigarette lighter used with a seven metre extension lead.

Please note safety precautions ! Wear a protective mask !
Minimum dimension of the entrance: 14 mm high and 90 mm broad
Minimum distance between bottom board and frames: 20 mm

2. Mode of action

A measured quantity of oxalic acid crystals are placed in the pan, then the appliance is inserted through the entrance of the hive, into the middle of the bottom of the hive, keeping the pan horizontal to prevent spillage of crystals. The insertion should be far enough so that the hexagonal metallic support is fully inside the entrance. If bees are clustered over the pan, they must be strongly encouraged to disperse into the interior of the hive by using smoke. The power is switched on and the heating action of the pan causes the oxalic acid to vaporise. The oxalic acid vapour pervades the hive and all the exterior of the bees and hive surfaces are covered by a deposit of a very thin layer of oxalic acid crystals. These fine crystals are tolerated well by the bees, but have a deadly effect on varroa mites.

3. Treatment

The treatment should only be be given when the majority of bees are within the hive, at a time when the bees have no heavy nectar flow, but the temperature should not be cool enough for the bees to be clustered, ie, below + 2°C. The VARROX-vaporiser is particularly suitable for use after the crop has been removed and the bees have ceased rearing brood.


The dose varies according to how strong the hive is... one gram of oxalic acid-dihydrate per full sized brood box. The measuring spoon supplied with Each VARROX-vaporiser, if filled with loosely and without compaction, corresponds to one gram of Oxalic acid-dihydrate. So use one spoonfull per brood box. In the case that a hive comprises a brood and a half arrangment of one brood box plus a super, then one and a half sponsful would appear to be a good compromise.

Placing the VARROX-vaporiser
The appropriate amount of oxalic acid-dihydrate is placed into the VARROX evaporator. Take care that the oxalic acid is not spilled when holding the VARROX-vaporiser at an angle or by twisting it. Afterwards, the appliance is Minimum dimensions of the entrance: 14 mm high and 90 mm broad. If insertion through the entrance is not possible because of the construction of the hive, use the opening of the diagnosis drawer where possible. In that case, the entrance of the hive must be shut tightly.

Hint:  Depending on the height of the entrance and the bottom of the hive, it is recommended to fit the VARROX-vaporiser in evenly by bending down both sides of the metallic support a few millimetres. The distance between the bottom of the hive and the heating element can be increased and the source of the heat is taken off the bottom.

Attention:  Due to the heating action of the pan, there is a danger of melting plastified varroa bars and synthetic hives. The VARROX-vaporiser reaches temperatures of up to 300°C and can create patches of heat on the bottom and frames.

Sealing up the hive
Seal the whole entrance (or diagnosis drawer) around the handle of the VARROX-vaporiser using strips of foam or cloth. Open floors should be shut tightly on the whole surface.

Duration of the treatment
After the hive is sealed up, the vaporiser should be switched on for 2 ½ minutes. As a rule, 2 ½ minutes are enough for the vaporisation of the oxalic acid. In the first colony that has to be treated, the heating time may be longer, because the vaporiser is still cold. An extra minute heating is required if using the extension lead.
One of the battery-clips of the lead should be constantly connected with the source of power using the contact of the second clip to switch the appliance on and off. It makes no difference if the plus or minus-poles are connected accordingly or not-the function of the heating is not reduced.
After switchIng off the VARROX-vaporiser, wait for about 2 minutes before the appliance is pulled out, so that the oxalic acid-vapour can settle down. Once removed, ensure that the entrance of the hive is shut tightly again and left shut for another 15 minutes. After taking out the VARROX-vaporiser, it should be cooled in a bucket of water, so that with the next use, no vaporisation begins before the appliance is inserted into the hive.

Hint:  With the use of several VARROX-vaporisers, bigger apiaries can be treated more time-effectively.

4. Oxalic acid-dihydrate (Oxalic acid-crystals) Oxalic acid is an unhealthy, toxic and corrosive substance. When filling the VARROX-vaporiser and during the treatment, it is absolutely necessary to wear protective glasses, a protective mask (FFP 3 S/L), gloves and long-sleeved clothes.

Working safety

Handling of oxalic acid

  • Oxalic acid can cause damage to health With both skin contact and if swallowed. Avoid contact with eyes and skin.
  • Vapours and dusts of the oxalic acid should not be inhaled.
  • Keep oxalic acid out of the reach of children.
  • Oxalic acid must be stored in its original container (with law-concurring labelling) in a safe place.

In the case of eye contact. immediately wash the acid out with water. If ingested immediately go to a doctor.

Working safety during the treatment

  • Treatments on colonies in a beehouse must only be made from outside through the entrances of the hives. During the treatment, the beehouse must be well ventilated. No person must be inside the beehouse.
  • WIth treatments of apiaries in the open, take care that the wind blows any escaping oxalic acid away from the user. The whole length of the lead should be used and the user should stay away rrom the hive.
  • The foam material used for sealing the hive must be handled with gloves. This avoids contact with the acid where it may have condensed on the inner side of the foam. The foam material must be washed out carefully with water before putting away.
  • After the treatment in the winter, oxalic acid-crystals are found on the bottom of the hive. This can be due to the absence of bee cleaning activity as found in the summer. Caution is therefore needed if mite fall is controlled after a treatment in the winter. Gloves and a protective mask should be worn. The rest of the oxalic acid will break down to water and carbon dioxide and will be cleaned by the bees in spring.
  • The VARROX-vaporiser is a powerful heater that generates high temperatures. The vaporisor must not be used near easily inflA. m. melliferaable materials. Always put the vaporiser on a sheet of non-flA. m. melliferaable material (i.e. metal). Never touch the metallic part of the vaporiser when in use. Caution: metallic parts may be hot for a long time after use. The vaporiser must never be switched on without supervision.

Purchase of oxalic acid-dihydrate

For the treatment, oxalic acid-dihydrate (C2H2O4 x 2 H20) CAS-No. 6153-56-6. EG-No. 205-634-3 has to be used. Normally available in pharmacies.

5. Concept of control

Treatment in brood free colonies
The VARROX-vaporiser can be used in brood-free colonies, notmally seasons without honey flow. With the VARROX-vaporiser a very good efficacy of > 96% can be reached and thus it can decimate the varroa-mite-population reliably to a very low level. Thereby, optimal preconditions for the new season are created for the bees.
If there is a mite fall of more than 1000 varroa mites caused by the treatment, or if it is uncertain whether there was brood in the colonies, a second treatment is recommended. The optimal time for it, is two weeks after the first treatment. Two or more treatments are very well tolerated by the bees.

Treatment of swarms / artificial swarms
Swarms and artifIcial swarms can be treated at any time.

Treatment of nucleus
Treatment of queenright nuclei should be carried out before the brood is sealed, if possible. Attention:  Queenless colonies react very conspicuously to the treatment with an increased activity in the hive and by leaving the hive.


  • Protective mask FFP 3 S/L
  • Extension lead (7m) with:
    • Plug for car cigarette lighter
    • Connecting piece for the battery-clips of the VARROX-vaporiser

Electrical supply

  • The VARROX-vaporiser must be operated with 12 volts. 12 ampere and cannot be directly plugged into a socket of 110 V or 220 V.
  • It runs on direct and alternating current. The following can be used as a source of power:
    • Car accumulator minimum 40 Ah (the accumulator and battery charger can be bought in DIY superstores)
    • Car cigarette lighter with extension lead (see accessories)
    • With a transformer (12 V 12 A)
  • The safety of the car cigarette lighter is usually good, enough for the capacity of the vaporiser (12 A or more). If the vaporiser is connected to the cigarette lighter for prolonged periods, the engine of the car may have to be run to avoid draining the battery.

Source of troubles

After the treatment there is still some acid left in the pan
Heating time is too short: Heat longer!
Accumulator is weak and produces too low a capacity: Charge accumulator!
Caution with synthetic hives and plastified varroa screens: With hives or varroa screens made of synthetic material. an isolation platter (minimum 4 mm thick) must be put under the appliance.
Possible burr-comb, which is sagging from below the frames, has to be removed, so that it is not in the way of the VARROX-vaporiser or too close. Maintain a minimum distance of 2 cm. Crumbs of wax on the bottom of the hive have to be removed.


Please, follow the instruction of use carefully. We do not assume any warranty for wrong application, reasons of unsatisfied efficacy or possible damages that are beyond the control of Andermatt BIOCONTROL AG.

Beekeeper Protection

It cannot be stressed too strongly that oxalic acid is an aggressive substance and needs to be treated with respect. Acid resistant gloves and goggles should be worn and an apron of the type used by mortuary attendants, along with wellington boots that have the tops covered by gaiters so that any falling liquid cannot fall into the boot. A respirator that has specialised organic acid filtering will be required in cases where the acid is sprayed or vapourised. Oxalic acid is also poisenous to humans by ingestion.

Written... 05, ?? November 2005,
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