Varroa sticky board mite drop calculator
A sticky board under the colony catches mites that fall off. Enter how many you counted and how many days the board was in, and this page gives the natural mite drop per day next to the line the USDA Agricultural Research Service quotes.
What the source says
The USDA-ARS Carl Hayden Bee Research Center sticky board page gives three facts this calculator uses. The screened board "typically is left in for 3 days." "Mite drop per day is calculated by dividing the total number of mites by the number of days the board was in the colony." And: "Typically, if 30 or more mites drop in a 24-hour period, then treatment is necessary." The calculator does the division and marks the 30 line. It gives no treatment advice.
Worked example
A board stays in for 3 days and you count 63 mites. 63 divided by 3 is 21.0 mites per day, 9 under the line of 30. The same count on a board left in for 2 days would be 31.5 per day, over the line. The number of days changes the answer as much as the count does, so write down when the board went in. Open this example.
Mites on the board that reach 30 per day
| Days in the hive | Mites counted |
|---|---|
| 1 | 30 or more |
| 2 | 60 or more |
| 3 | 90 or more |
| 5 | 150 or more |
| 7 | 210 or more |
Where sources disagree
- Time on the board. USDA-ARS says typically 3 days. The varroaresistant.uk mite calculator describes counting mite drop over 4 to 7 days with a protected bottom board. Both fit this calculator, which accepts 1 to 14 days.
- What the count means. USDA-ARS reads a drop of 30 per day as a reason to treat. The UK calculator uses the drop to estimate the mites in the whole colony by multiplying the daily drop by a factor. It mentions x100, and says x30 "may be more appropriate" when there is ample brood, and it warns that the estimate is unreliable in March, April, September and October when the brood nest is changing quickly. This page does not make that estimate. Use the UK page if you want it.
A different number: mites per 100 bees
A sticky board counts mites falling over days. An alcohol wash counts mites on a sample of bees on one day, which gives mites per 100 bees. The Honey Bee Health Coalition thresholds use that second number, so a sticky board count and a wash count do not compare directly. Follow the alcohol wash steps, then enter the result in the varroa mite calculator. After a treatment, compare two wash counts in the treatment check.