Nassenheider FAQ

Nassenheider Evaporator – Frequently Asked Questions (FAQ)

1. How does the Nassenheider Evaporator work?
The Nassenheider Evaporator is a slow-release formic acid delivery system designed to control varroa mites. It uses a wick system to gradually evaporate formic acid allowing the vapours to kill the mites.

2. How long does one application last?
A single 250ml dose of 65% formic acid typically lasts around 18 days with a No.2 wick and 7 days with a No.3 wick, depending on temperature and beehive conditions.

3. How much formic acid do I need per hive?
Each application requires 250ml of 65% formic acid, costing approximately $1.00 per hive per treatment. Freight charges for acid delivery are additional if applicable.

4. Where do I place the Nassenheider in the hive?
The evaporator should be placed on top of the brood frames, with a 75mm wooden rim to ensure proper airflow around the unit.

5. When should I use the Nassenheider for the best results?
For optimal varroa control, we recommend using the Nassenheider at the following times:
• Mid-Spring – First application
• Early Autumn & Mid-Autumn – Additional applications to ensure low mite loads heading into winter
• Summer & Winter – Oxalic acid-based treatments should be used instead, as formic acid is not recommended in extreme hot or cold temperatures.

6. How does temperature affect the Nassenheider's effectiveness?
Formic acid evaporation is temperature-dependent. The strength of the colony will have a large bearing on what temperature the acid will be when positioned directly above the brood nest. If temperatures outside are very low and that results in the acid being cold, then the evaporation slows down, making the treatment less effective. If temperatures above the brood nest get too hot, then excessive evaporation can harm the bees.
• Ideal temperature range for outside daytime temperatures: 15°C – 29°C
• Above 30°C: Increased risk of queen loss and brood damage
• Below 15°C: Evaporation slows down, reducing effectiveness

7. Can I use the Nassenheider during honey flow?
It is not practical to use the formic acid evaporator during a honey flow, because it has to be positioned between the brood box and the honey supers and may drive bees away from honey supers.

8. Is there a risk of queen loss with the Nassenheider?
The plastic base of the evaporator tray gives the brood and queen some direct protection from the vapour and causes gentle emission of the vapour over as large an area as possible. Formic acid is a powerful treatment, and in some cases, queens may be lost. Feedback from many beekeepers is that it is predominantly old queens that get superceded, and/or driven out the hive, especially in very high daytime temperatures. One theory is that the scent of the FA vapour overcomes the pheromones of an old queen, and the bees get confused and work to replace her. It is often considered a good way of replacing queens that are not up to a suitable standard.

9. Can I use the Nassenheider with weak colonies?
It is best to use formic acid treatments on strong, healthy colonies. Weak colonies may struggle to handle the exposure and could experience increased brood loss.

10. How do I refill the Nassenheider?
• Remove the empty bottle and replace it with a new 250ml bottle pre-filled with 65% formic acid.
• Ensure the wick is properly placed and not clogged.
• Close the hive carefully and allow the treatment to run its course.

11. Can I reuse the Nassenheider Evaporator?
Yes, the unit is reusable many times. Simply refill with fresh 65% formic acid and replace any worn-out wicks as needed.

12. Does formic acid leave residues in the hive?
No, formic acid naturally breaks down into water and carbon dioxide, leaving no harmful residues in wax or honey.

13. Can I use the Nassenheider alternatively with oxalic acid treatments?
Yes! A combination strategy using formic acid (Nassenheider) in spring and autumn and oxalic acid in summer and winter is an effective way to manage varroa mites without causing resistance.

14. Does the Nassenheider kill mites inside capped brood?
If the concentration of the vapour is high enough, it will harm the varroa mites under the cell caps. But this level of concentration is also tough on the bees and the larvae. If the hive is treated continuously for a minimum of 16 – 18 days with a medium concentration of vapour, that allows virtually all the mites to be killed when they are in the phoretic stage. (On the adult bees) And is more gentle on the bees & brood.

15. Does Formic Acid corrode metal items?
Yes, FA is naturally corrosive to mild steel and galvanised steel. Stainless steel is safe to use. The damage can be mitigated in the following ways:-
• Use the evaporator with a medium level of vapour concentration, not excessively high.
• Ensure hive mats are used with close fitting surfaces to reduce amount of vapour escaping near the roof.
• Remove emlock straps during the FA treatments. Add rocks to the roof instead.
• Use stainless steel queen excluders (if required) not galvanised steel excluders.
• Do not spill any FA on metal components when changing overempty bottles to full bottles.

16. Should the base of the beehive be vented or not during an application?
It is recommended to use a solid base with no vents during an application but to have the full width of the front entry open. Vented bases should be blocked with a sheet of Corflute or similar.

17. I don’t have 75mm wooden rims to go around the evaporator. What are my options?
Some beekeepers are cutting up old full depth boxes to get 3 rims per box, then paraffin dipping them for sterilization.
90mm top feeder rims can also be used. Click here for more info.
2 of the common feeders in NZ will fit upside down over the evaporator while in use.
See photos below.

Some beekeepers plan to trial the evaporator in one of their 7 litre top feeder bins. See a typical example above. 2 feeder bins in a 150mm high rim.
An absorbent cloth will be required under the outlet of the evaporator.
We are waiting on feedback to see if this is successful.