Varroa Mite Count Calculator: Wash, Sugar Roll or Sticky Board

HBHC's own worked example, 12 mites in a 300-bee alcohol wash, is 4.00 mites per 100 bees: above the 9th edition's threshold in every colony phase (1% in Dormant and Population Increase, 2% at Peak and in Decrease). A sticky-board count becomes mites a day, set against every published level with its region and season.

Reference tables

HBHC Table 1: varroa treatment thresholds by colony phase (mites per 100 adult bees), Tools for Varroa Management, Ninth Edition - June 11, 2026. *Note: Sample just prior to clustering to determine whether bees are healthy going into dormancy.

Colony phase	Immediate control not needed	Promptly control
Dormant*	<1%	≥1%
Population Increase	<1%	≥1%
Peak Population	<2%	≥2%
Population Decrease	<2%	≥2%

Published sticky-board levels, each for its own region and season. None is this site's; compare a count with the ones written for your area and season, then confirm with an alcohol wash.

Source	Region	Season	Level (mites a day)
NBU Managing Varroa, Figure 45 (values read from a chart)	UK	By month	See the month table
WOAH Terrestrial Manual	North America and Europe	early beekeeping season	1–10 a day
Ontario OMAFRA	Ontario, Canada	May	more than 9 a day
NBU author, BBKA News February 2025	UK	no season given	10 or more a day (more than a single digit)
Ontario OMAFRA	Ontario, Canada	August	more than 12 a day
USDA-ARS	US	no season given	30 or more a day
Mississippi State P2826	Mississippi	late summer	more than 40–50 a day
NC State	North Carolina	no season given	60–190 on one 24-hour board, by colony size

NBU Managing Varroa, Figure 45: daily mite drop by month (UK). Values read from the chart; a value is shown only where FIBKA's printed table gives the same number.

Month	No control needed below	Effective control urgently needed above
January	2	—
February	2	—
March	2	—
April	1	8
May	1	—
June	1	—
July	1	—
August	3	8
September	4	8
October	—	—
November	8	8
December	—	—

This calculator has two modes. Wash or sugar roll turns the mites counted in an alcohol wash, soap wash or powdered sugar roll into mites per 100 bees and compares that with the Honey Bee Health Coalition's current thresholds. Sticky board turns the mites that fell onto a board into mites a day and sets that figure beside every published level we could source; sticky-board mode opens it directly.

Worked example: HBHC's 12 mites in 300 bees

The calculator opens on the Honey Bee Health Coalition's (HBHC) own example from Tools for Varroa Management: "12 mites ÷ 300 bees = 0.04 mites per bee", then "0.04 X 100 = 4% (4 mites per 100 adult bees)". The tool shows 4.00%, the same figure to two decimals, and Promptly control in all four colony phases. The row for the older guidance reads At or above 3 per 100.

Every comparison is made exactly, with whole numbers, and never on the displayed figure. Three mites in 300 bees is exactly 1%, so it counts as reaching the 1% threshold, and the tool says Promptly control for the Dormant and Population Increase phases.

The displayed figure is cut off after two decimals rather than rounded. Eight mites in 401 bees is 1.995 mites per 100 and a little more, just under 2%. Rounding would print 2.00% beside a verdict of Immediate control not needed at the Population Peak's 2% threshold, which reads as a contradiction, so the tool prints 1.99% instead. A figure cut off this way never reaches a whole-number threshold that the exact count doesn't reach. Sticky-board mode does the same with one decimal, and its working says when a figure was rounded down.

Worked example: Ontario's sticky board, 36 mites over 72 hours

This example comes from the Ontario Beekeepers' Association, which explains that "a mite drop of 36 over 72 hours should be divided by 3 therefore 12 mites / 24 hours". Ontario's ministry works the same numbers in its own example. Neither names a month; the August used here is the calculator's default month, our choice rather than theirs.

With 36 mites over 3 days in August, the tool shows 12.0 a day and says it is above 4 of 8 published levels. It's above the August band of the UK's National Bee Unit (NBU), above the early-season range of the World Organisation for Animal Health (WOAH), above the single-digit line and above Ontario's May level, which is greyed because it's for May. It's Not above Ontario's August level of more than 12, because 12.0 equals it. It's below the USDA-ARS, Mississippi State and NC State levels. The short-count flag shows too, because 3 days is under the NBU's 7-day minimum.

This is an example, and the count is a comparison, not a verdict: the tool makes no treatment call of its own.

HBHC's thresholds by colony phase

HBHC sets its thresholds by colony phase, defined by what the colony is doing, not by month: "In some locations, there is one cycle of these four phases per year, in other locations there can be more than one cycle." So the tool never picks a phase from the date.

The phase picker uses HBHC's four labels. Table 1 prints the third phase as Peak Population, while the guide's definitions call it Population Peak; both names are HBHC's. The first table below the tool is Table 1, with its footnote about sampling just before clustering. If you don't know which phase your colony is in, the default, Not sure: compare all four phases, shows a verdict for each.

The older 3% level

Several research and extension sources give an action level of 3 mites per 100 bees. USDA-ARS says "Treatment is recommended if the sugar shake or alcohol wash results in 3 mites per 100 bees", and Mississippi State's P2826 says "Most beekeepers prefer to use the 3 percent end of the range as the action threshold." UF/IFAS's Florida calendar (IN848) says "Consider treating when Varroa levels reach 3%", and Cornell's Northeast calendar says, for part of the year, "if you find three or more mites (per 100 bees) from a sugar shake, ether roll, or alcohol wash, you will want to treat." Cornell uses a lower two per 100 in other months.

HBHC's current Table 1 is lower than 3 in every phase, so the tool shows the 3-per-100 level only on a row labelled as older guidance, with these four sources named on the next row.

Taking the sample

HBHC's method uses about 300 bees, and the tool adds its note when you enter fewer: "Using fewer than 300 bees will not give you an accurate sample." For a sugar roll it adds HBHC's comparison, "The alcohol/soap wash method is a more reliable method than the powdered sugar shake."

Mississippi State gives useful background on where the mites are: "typically one-third of the mite population resides on adult bees and two-thirds are in capped brood". The tool doesn't apply that split. It uses no correction factor for a sugar roll and never estimates the total number of mites in the colony.

Sticky boards: mites a day, never a percentage

USDA-ARS describes the arithmetic: "Mite drop per day is calculated by dividing the total number of mites by the number of days the board was in the colony." The tool also takes hours, for boards read after a day or two.

HBHC lists sticky boards in "Table 2: Less Reliable Sampling Methods for Assessing the Number of Varroa Mites in Bee Colonies", and says "The Honey Bee Health Coalition does not recommend relying on the methods identified in Table 2." Its one sourced use for a board is "Useful to check mite population trends or as quick check to confirm treatment effectiveness."

Each row of the ladder is one source's level for its own region and season: the NBU's UK month bands, WOAH's 1 to 10 a day early in the season, Ontario's levels for May and August, the NBU author's single-digit line, the USDA-ARS level of 30 a day, Mississippi State's late-summer range of 40 to 50 a day, and NC State's 60 to 190 on one 24-hour board, depending on colony size. The second table below the tool lists them all. They differ because, as Mississippi State puts it, "The economic thresholds estimated for using this technique vary widely from region to region." WOAH goes further: "the damage threshold of varroosis in A. mellifera cannot be established".

The NBU month bands are values read from a chart, Figure 45 of the NBU's Managing Varroa leaflet, whose values aren't printed in the leaflet's text. A value is shown only where the printed table of the Federation of Irish Beekeepers' Associations (FIBKA) gives the same number, so some months show only the lower line, and October and December show none. The leaflet explains its basis: "Figures quoted are based on the mathematical model of mite populations and aim to maintain a level of less than 1000 mites/colony during the beekeeping season."

The tool flags three things. A count under 7 days is short, because NBU Fact Sheet 13 says "Due to variability in the daily mite mortality, 7 days is the minimum monitoring period." A broodless colony gets the same fact sheet's warning: "NB: This method is unreliable where a colony is broodless or collapsing from varroosis". With a treatment in the hive, nothing is compared, because, as FIBKA notes, "Note that these figures are for Natural Mite Fall with no Treatment."

A board count gives no percentage and no estimate of total mites. HBHC's reason: "Difficult to interpret number of mites as an estimate of mite population, since it is a whole-colony measure and not a per-bee measure." Sticky-board mode always shows a Confirm with an alcohol wash link that switches to the wash mode.

Keeping a record

This calculator keeps nothing between visits. To follow one colony over a season, the inspection log saves each hive's wash, sugar-roll and sticky-board counts in your browser, works them out with this calculator's arithmetic, and lists them by date so a rising count stands out.

What this calculator doesn't do

It names no treatment products or doses; for treatment options, see the HBHC guide. It doesn't diagnose a colony. It doesn't map months to HBHC phases, and it doesn't shift months for the Southern Hemisphere, because no saved source gives either.

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Sources (14)

1. Honey Bee Health Coalition, Tools for Varroa Management, 9th edition (June 11, 2026) honeybeehealthcoalition.org
2. USDA-ARS Carl Hayden Bee Research Center, Sticky Board ars.usda.gov
3. USDA-ARS Carl Hayden Bee Research Center, When to Sample ars.usda.gov
4. Mississippi State University Extension, Managing Varroa Mites in Honey Bee Colonies (P2826) extension.msstate.edu
5. UF/IFAS Extension, Florida Beekeeping Management Calendar (IN848) edis.ifas.ufl.edu
6. Cornell University, Beekeeping Calendar for the Northeast cals.cornell.edu
7. NC State Extension, Managing Varroa Mites in Honey Bee Colonies content.ces.ncsu.edu
8. Ontario Ministry of Agriculture, Food and Agribusiness, Varroa mites ontario.ca
9. Ontario Beekeepers' Association, Varroa sampling (2012) ontariobee.com
10. World Organisation for Animal Health, Terrestrial Manual, Varroosis of honey bees woah.org
11. UK National Bee Unit, Managing Varroa (advisory leaflet) nationalbeeunit.com
12. UK National Bee Unit, Fact Sheet 13: Estimating Varroa mite populations (April 2024) nationalbeeunit.com
13. BBKA News, February 2025: Varroa monitoring and treatments (National Bee Unit) nationalbeeunit.com
14. Federation of Irish Beekeepers' Associations, Guidelines on Varroa Destructor irishbeekeeping.ie