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Varroa mite count calculator

Enter your mite count: the calculator gives the mites per 100 bees and compares them with the Honey Bee Health Coalition’s threshold for your colony’s phase, so you know whether to control now or keep sampling.

The HBHC notes that thresholds are an evolving science and often depend on the situation and the region. Ask your state apiary inspector or extension service if in doubt.

Sampling method
cup
½ cup of lightly packed bees ≈ 300 bees.
Leave empty to use the cup measure.
Control promptly from 2 to 3 mites per 100 bees: this is when the bees that will overwinter are raised.

Result

  • 2%mites per 100 bees
  • 300bees in the sample
  • Promptly control

Over the HBHC threshold for this phase. Control mites promptly, choosing a method that fits the season and the label rules, with help from your state apiary inspector or extension service if needed. Sample again afterwards to check it worked.

How it is calculated

The formula

bees in the sample = cups × 600 (½ cup ≈ 300 bees)
mites per 100 bees = 100 × mites ÷ bees

The Honey Bee Health Coalition’s own example: 12 mites in a 300-bee sample is 4 mites per 100 bees, or 4 %.

HBHC thresholds (mites per 100 adult bees)

Colony phaseImmediate control not neededPromptly control
Dormantunder 1over 1
Population increaseunder 2over 2 to 3
Peak populationunder 2over 3
Population decreaseunder 2over 2 to 3

At peak population, a count between 2 and 3 falls between the two columns: the calculator shows it as “at the threshold”. Where the guide gives a range (2 to 3), the calculator treats 2 as the threshold.

How to take the sample

Take about 300 bees, ½ cup lightly packed, from one to three brood frames, without the queen. For a wash, swirl the jar for at least a minute, pour the liquid through a mesh onto a white plate and repeat. For a sugar roll, add about two tablespoons of powdered sugar, shake for at least a minute, wait a few minutes, then shake the mites out onto a plate. Read more in our guide to varroa mites.

Frequently asked questions

How many mites per 100 bees is too many?

The Honey Bee Health Coalition sets the threshold by colony phase: above 1 mite per 100 bees in a dormant colony, from 2 to 3 per 100 while the population grows or declines, and above 3 per 100 at peak population. Below 2 per 100 in the active season, immediate control is not needed.

How many bees are in a half cup?

About 300 adult bees, lightly packed, which is the sample size the Honey Bee Health Coalition recommends. Fewer than 300 bees does not give an accurate sample. Take the bees from a brood frame, and make sure the queen is not among them.

How do I calculate mites per 100 bees?

Divide the number of mites by the number of bees in the sample and multiply by 100. With a half cup of about 300 bees, that is simply the mite count divided by 3: 12 mites in 300 bees is 4 mites per 100 bees, or 4 %.

Alcohol wash or sugar roll: which is better?

Both use the same half cup of bees and the same thresholds. An alcohol or soapy water wash kills the sample but gives more consistent counts. A powdered sugar roll returns the bees to the hive, with more variation from one count to the next.

Does the month tell me the colony phase?

Only roughly. The phase depends on your region and the colony: a colony in Florida may never stop raising brood, while one in Maine is dormant for months. Choose the phase your colony is in; the calculator only suggests one from the month.

Sources

  1. Tools for Varroa Management: A Guide to Effective Varroa Sampling & Control (8th edition, August 2022), Honey Bee Health Coalition

Calculators