How to do an alcohol wash for varroa
An alcohol wash shakes the mites off a sample of bees so you can count them. Two extension guides give the steps, and they differ in a few details. Both are laid out below, followed by a table that turns a mite count into a percentage for either sample size.
The steps
- Find the queen and set her aside, in a nuc box or on a frame you will not shake. Mississippi State uses a cardboard nuc box for this.
- Shake or scoop bees from a brood frame into a bucket, then measure half a cup of them into a jar with a solid lid. Mississippi State asks for nurse bees from combs with uncapped larvae.
- Cover the bees with rubbing alcohol and close the lid.
- Shake the jar hard. Michigan State says 60 seconds, Mississippi State 3 to 5 minutes.
- Swap the solid lid for a mesh lid and pour the alcohol through it into a white pan, so the reddish mites show.
- Wash again, as the section below describes, and add the mites from every pour together.
- Count the mites, and count the bees if you can.
- Divide mites by bees and multiply by 100.
Where the two guides differ
| Detail | Michigan State | Mississippi State |
|---|---|---|
| Bees in half a cup | about 300 | 400 |
| Alcohol | Isopropyl, 35% to 70% | Rubbing alcohol, 70% |
| Shaking | 60 seconds | 3 to 5 minutes |
| Washes | Two rinses | Until no more mites come off |
| Counting the bees | For best accuracy | Divides by 400 |
Sources: Michigan State University, Varroa mite monitoring alcohol wash (Chapman, updated 2025), and Mississippi State University Extension, Sampling for Varroa Mites Using an Alcohol Wash (Harris, Publication 4049).
If your local extension or bee club gives different numbers, follow them. The guides were written for beekeepers in Michigan and Mississippi.
Why the number of washes matters
The first pour does not carry every mite. Mississippi State's answer is to keep washing until a pour brings up no more, and to add all the pours together. Michigan State stops at a second rinse. Count the mites from each pour into the same total before you divide, and use the same routine every time so your counts can be compared from one visit to the next.
From a mite count to a percentage
This is mites divided by bees, times 100, using the same sum as the varroa mite calculator. The table assumes the sample holds exactly 300 or 400 bees. Mississippi State's worked example is 28 mites in 400 bees, which is 7 percent.
| Mites counted | In 300 bees | In 400 bees |
|---|---|---|
| 1 | 0.3% | 0.25% |
| 2 | 0.7% | 0.50% |
| 3 | 1.0% | 0.75% |
| 4 | 1.3% | 1.00% |
| 5 | 1.7% | 1.25% |
| 6 | 2.0% | 1.50% |
| 8 | 2.7% | 2.00% |
| 9 | 3.0% | 2.25% |
| 10 | 3.3% | 2.50% |
| 12 | 4.0% | 3.00% |
| 15 | 5.0% | 3.75% |
| 20 | 6.7% | 5.00% |
Mites needed to reach a threshold
Half a cup of bees is a loose measure, so one jar can land on either side of a line. Whole mites it takes to reach 1, 2 and 3 per 100 bees:
- 1 per 100: 3 mites in 300 bees, 4 in 400.
- 2 per 100: 6 mites in 300 bees, 8 in 400.
- 3 per 100: 9 mites in 300 bees, 12 in 400.
So 9 mites is 3.0 percent if the jar held 300 bees and 2.25 percent if it held 400. Counting the bees settles it. The calculator with 9 mites filled in shows the result against the thresholds.
After the count
This page only covers the count. What to do about a high one is a label and local advice question, and the product label is the law. Fall timing depends on brood, see when to treat with oxalic acid in fall. The alcohol kills the bees in the sample, so wash a sample you can spare.