Varroa Mite Population Simulator: See Your Mite Load Over the Season
Varroa mites roughly double every month while there is brood in the hive, and most of them spend most of their lives sealed under wax cappings where no treatment can touch them. That combination is why the same oxalic acid treatment can look useless in August and near-perfect in December. This simulator starts from your mite wash, grows the population day by day through winter, and shows what every treatment date on your plan does to it, so you can fix the timing before the bees pay for it.
Tool Varroa Mite Population Simulator
What the simulator is modeling
It runs one day at a time from your wash date to the following March. Each day it updates three things:
- Brood. How much capped brood the colony has, from full in late spring and summer to none in your climate's broodless window. This drives both mite growth and how many mites are hidden.
- Mites. With full brood the population grows about 2.2% a day, roughly doubling every month. With no brood there is no reproduction and the mites slowly die off. About 65% of the mites are sealed in cells at full brood; that fraction falls as brood shrinks in the fall and is zero when the hive is broodless.
- Bees. The adult population follows a typical temperate curve, peaking near 45,000 in July and dropping toward 12,000 in winter. The number you see, mites per 100 bees, is exposed mites divided by adult bees, which is what an alcohol wash measures.
Treatments act on the day you schedule them. Oxalic acid vaporization removes about 95% of the exposed mites that day and none of the sealed ones. Oxalic acid dribble removes about 90%. A brood-penetrating treatment (formic acid) removes about 70% of all mites over 14 days. Caging the queen takes the brood to zero over 24 days, which is why it is paired with a single vaporization on release day.
What to look for. The shaded band is when winter bees are raised. The mite level inside that band, not the level on New Year's Day, decides whether the colony is alive in February. If your plan's line is above the threshold in the band, move the series earlier. If it is low in the band but rising by December, add one vaporization in the broodless window.
Where the numbers come from
Growth rates and brood fractions are drawn from the varroa population literature (Martin's models of mite population dynamics; Rosenkranz, Aumeier and Ziegelmann's review of varroa biology and control) and from field efficacy work on oxalic acid (Al Toufailia, Scandian and Ratnieks reporting 97% efficacy of vaporization in broodless colonies). The thresholds follow the Honey Bee Health Coalition's guidance of 2 mites per 100 bees in spring and 3 per 100 from late summer on. The model simplifies real colonies: it does not include drifting mites from collapsing neighbors, swarming, or a queen that simply out-lays your assumptions. Treat it as a way to reason about timing, then confirm with a wash.
Frequently asked questions
How fast do varroa mites multiply?
With brood in the hive, a mite population roughly doubles every month. A colony at 1 mite per 100 bees in May can be at 8 or more per 100 by September without treatment, which is the level that produces damaged winter bees and a dead hive in January.
Why does the simulator show a single oxalic acid treatment doing so little in August?
Because in August most of the mites are sealed under brood cappings, where oxalic acid cannot reach them. A single vaporization only removes the mites on adult bees that day. That is not a flaw in the product; it is why a series across the brood cycle, or a single treatment in the broodless window, does so much more.
What mite level is dangerous?
Most extension services use 2 mites per 100 bees as the treatment threshold in spring and summer and 3 per 100 in late summer and fall. Above 5 per 100 going into winter-bee rearing, colony loss becomes likely. The simulator draws these thresholds on the chart.
Is this simulator accurate for my hive?
It is a model, not a measurement. It uses published growth rates and brood fractions for a typical temperate colony and adjusts them for your climate and treatment plan. Use it to understand timing and compare plans; use a mite wash to know what is actually in your hive.
What are winter bees and why does the chart shade August to October?
Winter bees are the long-lived generation raised in late summer and fall that has to carry the colony to spring. If they are raised while mites are high, they are born damaged and die early. The shaded window is when they are being raised, and the mite level then is what decides whether your colony is alive in January.
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Related reading
- The varroa mite life cycle: why timing beats dosage
- Why colonies die in January: it's usually mites, and the damage was done in August
- How to do a mite wash
- Does oxalic acid vaporization work? What the studies show
- Every varroa treatment compared
Sources: Martin, S.J., "A population model for the ectoparasitic mite Varroa jacobsoni in honey bee colonies", Ecological Modelling 109:267–281, 1998 · Rosenkranz, P., Aumeier, P. & Ziegelmann, B., "Biology and control of Varroa destructor", J. Invertebr. Pathol. 103:S96–S119, 2010 · Al Toufailia, H., Scandian, L. & Ratnieks, F.L.W., "Towards integrated control of varroa: 2) comparing application methods and doses of oxalic acid", J. Apic. Res. 54(2):108–120, 2015 · Honey Bee Health Coalition, Tools for Varroa Management, 8th ed.
Timing is the whole game. Make the treatment easy.
A series across the brood cycle or one shot in the broodless window is a 20-second job per hive with an InstantVap oxalic acid vaporizer. Put the dates on your calendar with the Treatment Series Planner and stock EZ-OX before the window opens.
General beekeeping information from Lorob Bees, not a substitute for a product label or your state apiary inspector. Always read and follow the label of any product you use in a hive.