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Randy Oliver's Varroa Calculator

Updated: Apr 30

The varroa model that Randy Oliver has developed and graciously made available for beekeepers to use is truly brilliant. I found it both informative and empowering to test hypothetical mite treatments and see how they would impact the varroa populations in my colonies across an entire year before committing to a strategy. This tutorial will help you learn to use the tool yourself so that you have the very best information as you make decisions around mite management.

You can download your own copy of the Varroa Model here:

What I really love about this tool is that there is no 'one way' to achieve a sustainable result. You can use this model to create a strategy that aligns with your personal philosophy and preferences and also produces a positive outcome for your bees.

The only way to get an appreciation of how this tool works is to see it in action. In the video below, I explain how to start using the model yourself and I talk through some common scenarios and how the model predicts their outcomes.

Here are a few notes and screen shots that will help you as you start to use this tool for yourself.

Before you start inputting any treatments, you need to make sure that the data in the three little green boxes below reflects the reality of YOUR colonies.

Here are the descriptions of the various colony types:

(I used B in the video because we have a 5+ month winter with little forage and little brood)

How to determine your starting mite population:

Option 1: If you have recently done a mite test (this model is based on alcohol wash), then adjust the starting mite population until the mite test number and date when you did the test are both accurate (ex. If you did an alcohol wash on April 1 and got 3 mites in 1/2 cup of bees, you need to make the number in the white box above April 1 show as 3. You do this by changing the starting mite population).

Option 2: If it's the middle of winter and you're just testing some hypotheticals, consider your winter treatments. If you've done a couple rounds of OAV since fall, start with 100. If your last treatment was September or earlier, start with 300 (this is my own advice; I'm not sure what Randy would advise).

Here are the descriptions for the mite immigration numbers:

In the video, I used 2 because we have neighbours who do not treat. Upon further thinking, I have decided that 3 or 4 might be more accurate for our town bee yards and when I plug that in, the model does behave more like what we really see.

Now you're ready to start inputting treatments

Find the treatment below and input the % mite reduction in the yellow box that corresponds to the date when you would do that treatment. Where there is a range, I like to split the difference.

Notice your ending mite population at the right end of the graph in red.

Ideally, you want this number to be under 100. You can test the sustainability of any mite strategy by inputting the ending mite population into the starting mite population box (because you're starting the new year with that many mites). This will give you the best indication of whether your strategy is sustainable across a full year.

Accounting for mite resistant stock

If you feel strongly that your bees are of very resistant stock, you can adjust for that in the model. I would only do this if you have seen across multiple years that they survive with less intervention than the majority of bees. Please don't just take a bee breeder's word for it that their queens are varroa resistant/hygienic).

To adjust for this, first type the word "custom" into the empty green box. Then, change the 10% at the very bottom to a higher number. Randy notes that 50% would be for very strong resistance.

Try it!

I hope that I haven't made this seem complicated. I am truly so excited about this tool that I want to shout about it from the rooftops. I wish that every beekeeper would test their mite strategy against this model before putting it into action. This gives us the knowledge to be proactive in our management in a way that is well-informed and not just guess-work or taking someone else's word for it.

Looking for more?

Looking for more beekeeping education? You can find my virtual, on-demand course Intermediate Beekeeping for Year 2 and Beyond at

Or if you'd prefer a more tailored experience, you can join my mentorship group at


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