Oxalic acid strips against varroa: how the new treatment works

Since summer 2025 there has been a new weapon against the varroa mite in Germany: the oxalic acid strip. It works for weeks and needs no evaporator. We explain in detail how it works, when it plays to its strengths — and where its limits lie.

For years, summer varroa treatment mainly meant one thing: formic acid and evaporators, with everything that entails — the right temperature window, correct dosing, constant checking. Since summer 2025 an alternative has been approved in Germany that simplifies much of this: the oxalic acid strip, on the market in the EU as Calistrip Biox. It is the first approved product of its kind and is currently generating a lot of discussion among beekeepers. We put into context what it can do — and what it cannot.

What is new about the strip?

You probably know oxalic acid as a winter treatment: trickle or spray once, a short and powerful effect on the mites sitting on the bees. This is exactly where the strip comes in — only differently. Instead of a single application, it releases the active ingredient over a long period.

In practice, you hang the impregnated strips between the combs where the bees sit. There they release oxalic acid continuously for up to six weeks — and independently of the outside temperature. Each strip contains a defined amount of oxalic acid dihydrate, which the bees gradually distribute in the colony. This temperature independence is the real trick: while formic acid depends on 15–30 °C and struggles in a heatwave or cold spell, the strip simply keeps working.

The decisive catch: capped brood

As handy as the strip is, it does not get around one physical fact: oxalic acid cannot penetrate capped brood cells. It only reaches the mites currently sitting on the bees (the so-called phoretic mites) — not those safely multiplying in the brood. And in summer, most mites are exactly there.

That is why the manufacturer recommends use in low-brood or broodless colonies. In practice this means the strip plays to its strengths when you have reduced the amount of brood beforehand — for example through brood removal or caging the queen — or in late autumn when the colonies become broodless on their own. If you place the strip in midsummer in a colony full of capped brood, the effect remains patchy because new mites keep emerging from the brood.

How do you use the strip sensibly?

You get the most out of it if you place the strip in a broodless or deliberately low-brood phase. Two typical approaches: first, the combination with brood removal in high summer — you remove the capped brood, hang in the strip and thus catch a large share of the mites in the phoretic phase. Second, use in the broodless late autumn as a convenient alternative to classic trickling. The exact number of strips depends on the colony size — stick strictly to the package insert.

Who is it worth it for — and what does it cost?

The strip is an interesting addition to the toolbox, not a blanket replacement for everything. Its advantages: easy handling (insert once instead of refilling for days), no dependence on the weather and good tolerability when used correctly. On price, expect around 60 euros per pack, i.e. about 12 euros per colony and treatment — more than home-mixed oxalic acid, but the convenience is noticeable.

As the strips are still young in Germany, bee institutes and beekeepers are currently gathering the first solid practical experience. It is worth keeping an eye on the recommendations of your regional bee institute. And as with every veterinary medicine: apply strictly according to the approval and package insert, document every treatment in the treatment record, and check the success afterwards with a mite board.

Conclusion

The oxalic acid strip makes oxalic acid treatment more flexible and weather-independent — but it changes nothing about the basic rule that oxalic acid only works properly with little or no brood. Timed correctly, it is a welcome enrichment; used wrongly, you waste its potential.

Source

Approval and application notes for oxalic acid strips (Calistrip Biox) in Germany and Austria, since summer 2025; assessments among others by the Kirchhain Bee Institute (LLH) and specialist articles in bienen&natur.