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Varrox Evaporator Instruction Leaflet, as Supplied By Thorne

Also known as Varrox vaporiser

This page has been archived. It is retained for historical purposes and should not be relied upon for information

This Instruction leaflet is an electronic facsimile of an original, that was supplied, along with a Varrox evaporator, by the UK bee appliance dealer Thorne, the original picture was of too poor a quality to reproduce, so it has been replaced with a similar image. 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 with the chemicals mentioned, is legal in your own area or country and take notice of the warnings regarding oxalic acid. The white portion of this page is laid out in the same way as the leaflet and the text has been left uncorrected (it is a translation). Because the material used can be dangerous and the document below could be mis-interpreted, I have produced an English version, I have attempted to write it using UK terminology rather than translating the words. If, however, anyone reading my version does not agree with my interpretation of the text below, please get in touch and the text can be changed, because that may help others to understand more deeply.

The large hexagonal wings behind the evaporator pan are to ensure that the pan stays horizontal when inserted into the hive, this ensures that all of the oxalic acid crystals are evaporated and none are spilled. The wings also act to dissipate the heat from the pan to avoid the handle getting too hot.



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

Information stand:
March 2002

1. Appliance

The VARROX-vaporiser consists of a heater, a metallic support and 3 m of read with 2 battery- clips. It has an output or 150 W. The power source can either be an accumulator (car battery. 12 volt, 12 ampere, capacity > 40 Ah) or a car cigarette lighter used with an 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: 2 cm

2. Mode of action

Oxalic acid is filled in the pan, then the appliance is inserted through the entrance of the hive. Due to the heating action of the pan, the oxalic acid liquefies and vaporises. Oxalic acid vapour fills the hive and all the bees and surfaces are then covered with 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 not be made during heavy bee flight. Furthermore, the temperature should not be below + 2°C. The use of the VARROX-vaporiser is particularly suitable for the follow up treatment in brood-free colonies.


 Type of hiveOxalic acid-dihydrateMeasuring spoon*
 One-room-hive (e.g. warm way, one-storey)1g1
 Two-room-hive (e.g. two-storey)2g2

*One spoon, filled loose and without pressing, corresponds to one gram Oxalic acid-dihydrate. Each VARROX-vaporiser is supplied with a measuring spoon.

Placing the VARROX-vaporiser
The appropriate amount of oxalic acid-dihydrate is placed into the VARROX-vaporiser. 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 inserted through the entrance of the hive into the middle of the bottom of the hive, until the metallic support is fully inside. If bees are sagging over the pan, they must be strongly encouraged upwards with smoke. The treatment should only be used in hives normally occupied with bees. It must not be used at close range of wax (minimum distance 2 cm).
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 from 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 inflammable materials. Always put the vaporiser on a sheet of non-flammable 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, normally 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.


Page created 2002

Page archived 05/11/2020

Written... 02, 03 November 2005, Revised... 17 August 2006,
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