Should I Sample Brood or Nurse Bees for a Mite Wash?

Sampling forager bees returning at the entrance underestimates infestation by an average of 50% versus nurse bee sampling. This is one of the most consequential technique differences in varroa monitoring, and it's one of the least understood.

Here's why sampling location matters so much, and exactly how to collect from the right place.

TL;DR

• A valid mite count sample requires approximately 300 bees from the brood nest for statistically reliable results
• alcohol wash is 15-20% more accurate than sugar roll for detecting mite infestation levels
• The calculation is: (mites counted / bees in sample) x 100 = infestation percentage
• A 2% threshold triggers treatment in spring/summer; 1% is the fall action threshold
• Count at least once per month during active season; increase to every 2 weeks if levels are near threshold
• Log every count in VarroaVault to build a trend dataset that shows whether populations are rising or stable

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Why Mite Distribution Isn't Uniform Across the Colony

Varroa mites have a strong preference for brood cells over adult bees. During the active season, 80-90% of mites are in capped brood at any given time. The remaining 10-20% that are phoretic (riding on adult bees) aren't distributed evenly across the colony population.

Nurse bees that tend brood cells are the primary pathway by which mites find new cells to infest. A phoretic mite rides on an adult bee and waits for that bee to enter a brood cell to care for larvae. Nurse bees, which spend most of their time near and in brood cells, carry 3-4x more phoretic mites than foragers or bees at the entrance.

This makes biological sense: mites that hitchhike on nurse bees are more likely to reach new brood cells than mites on foragers that spend most of their time outside the hive.

The Sampling Error of Collecting From the Entrance

When you scoop bees from the landing board or collect returning foragers at the entrance, you're getting the bees with the lowest mite loads in the entire colony. These bees have spent the day foraging outside the hive. They're old bees (10-30 days old) that haven't been in the brood area recently.

A sample of 300 entrance foragers might show 1.5% infestation when the actual colony mite load, measured from the brood nest, is 3% or higher. You've missed the threshold. You don't treat. The colony continues to build toward collapse.

This 50% underestimation average means that if you're making treatment decisions from forager samples, you should effectively double your count to estimate the true infestation. Better yet: sample from the right place.

Where to Collect for an Accurate Sample

The brood nest: The central frames in the colony where the queen is laying and nurse bees are clustered. In a standard Langstroth hive, this is typically the middle 3-5 frames of the lower brood box.

How to identify brood nest bees without accidentally catching the queen:

1. Pull a frame from the center of the brood nest area.
2. Look for the queen before shaking. If she's on this frame, set it aside gently and use the adjacent frame.
3. Hold the frame over your open collection jar (a wide-mouth jar with a mesh lid works well).
4. Shake firmly. The nurse bees on brood frames are reluctant to leave and require a sharp shake.
5. Target 300 bees. For a standard alcohol wash jar, 300 bees fills roughly half the jar.

Avoiding the queen frame: The queen is often in the center of the brood nest. Before shaking any frame, check both sides for the queen. If you're not finding her visually, be careful when shaking; you don't want her in your sample jar.

The Difference in Practice

Here's how the sampling error plays out in real numbers:

A colony with a true 3% infestation rate (9 mites per 300 bees in the brood nest):

• Brood nest sample: 8-9 mites in 300 bees = 2.7-3% reading (accurate)
• Entrance forager sample: 4-5 mites in 300 bees = 1.3-1.7% reading (undercount by 50%)

With the brood nest sample, you treat. With the forager sample, you don't. Six weeks later, the colony that didn't get treated is at 6-8% and heading toward collapse.

Does VarroaVault Track Where You Sampled?

Yes. VarroaVault's count log includes a sampling location field. You can record whether you collected from:

• Brood nest
• Middle box (non-brood)
• Entrance
• Other location with notes

If you log a sample from the entrance or a non-brood location, VarroaVault displays a flag noting that the count may underestimate true infestation. This helps you interpret borderline results (a 1.5% entrance sample that might be a 2.8% true infestation) and make better treatment decisions.

The sampling quality flag also appears in your efficacy calculations. If your pre-treatment count was taken from the entrance and your post-treatment count was from the brood nest, the efficacy comparison would be misleading. Consistent sampling location is noted in the calculation.

Sugar Roll vs. Alcohol Wash: Does Location Matter for Both?

Yes. The same sampling bias applies to sugar roll methodology. A sugar roll from brood nest bees gives you a more accurate picture than one from entrance foragers.

The difference is that sugar rolls generally show 30-40% fewer mites than alcohol washes on the same colony anyway (because the sticky sugar coats the mites and some cling to bees during counting). Combining a sugar roll with forager sampling gives you two sources of undercount stacking in the same direction.

If you're using sugar roll, be especially careful to sample from the brood nest, and consider using the alcohol wash when making critical treatment threshold decisions.

See also: How to do a mite wash and Mite wash calculator.

Frequently Asked Questions

Where should I collect bees for the most accurate mite wash?

Collect from the center of the brood nest, specifically from frames where nurse bees are caring for capped brood. These bees carry 3-4x more phoretic mites than foragers. Avoid collecting from the entrance, landing board, or supers. A 300-bee brood nest sample gives you the most accurate picture of your true infestation level.

Does it matter which bees I sample?

Yes, significantly. Forager bees at the entrance carry 50% fewer mites on average than nurse bees in the brood nest. If you sample from the entrance, your count will underestimate the true infestation by roughly half, potentially causing you to miss treatment threshold and let the colony continue to build toward a dangerous infestation level.

Does VarroaVault track where I collected my bee sample?

Yes. VarroaVault's count log includes a sampling location field. If you log a count from the entrance or a non-brood location, the app displays a flag noting potential underestimation. For counts logged from the brood nest, no flag appears and the reading is treated as an accurate infestation estimate.

How soon after treatment can I run a post-treatment mite count?

Wait 2-4 weeks after the treatment ends before running a post-treatment count. Counting too soon (within a week of treatment removal) may show mites still dying or emerging from the last brood cycle. Waiting 2-4 weeks allows emerging bees from brood that was capped during treatment to fully emerge and any surviving mites to become detectable in a new count.

What should I do if my mite count results seem unusually high or low?

If results seem surprising, repeat the count within 1-2 weeks before making a treatment decision based on a single outlier result. Confirm you sampled from the brood nest center (not outer frames), used the correct sample size (approximately 300 bees), and shook vigorously for the full 60 seconds. Consistent sampling technique is the most important factor in count accuracy.

Can I count mites from a sticky board instead of doing an alcohol wash?

Sticky board counts measure mite fall rate over 24-72 hours, which correlates with infestation level but is not a direct measure of infestation percentage. Sticky board results cannot be converted to an accurate percentage without calibration, and they are less reliable than alcohol wash for treatment decisions. Use sticky boards for general population monitoring but rely on alcohol wash counts for threshold decisions.

Sources

• American Beekeeping Federation (ABF)
• USDA ARS Bee Research Laboratory
• Honey Bee Health Coalition
• Penn State Extension Apiculture Program
• Project Apis m.

Get Started with VarroaVault

An alcohol wash gives you the number. VarroaVault turns that number into a decision. Log your count, get an instant threshold comparison, and build a monitoring history that shows you whether mite levels are rising or stable across your entire operation. Start your free trial at varroavault.com.