Varroa in Swarms and Captured Colonies: Monitor Before You Assume
New beekeepers who catch a swarm often ask whether swarms have varroa. The answer is yes, they do, just fewer than the colony they came from. Swarms typically have 30-50% lower mite levels than parent colonies due to the broodless transition period, but that still means some mites, and those mites will grow once brood rearing resumes.
The bigger mistake is assuming a caught swarm is mite-free and skipping the baseline count. That assumption is how people end up surprised when a swarm they installed in May collapses in October.
TL;DR
- Natural swarms carry mites with them but typically have lower initial mite loads than the parent colony
- The swarm cluster has no capped brood for 3-5 weeks after departure, creating a natural broodless period ideal for treatment
- Parent colonies lose about 30-40% of their bee population to swarming, which can cause a temporary mite level spike
- Test parent and swarm colonies separately within 2 weeks of swarm departure
- Swarm season (April-June in most regions) coincides with rapid mite population growth in strong colonies
- Log swarm events and post-swarm mite counts in VarroaVault to track how swarming affects mite dynamics
Why Swarms Have Lower Mite Levels
When a swarm leaves a colony, it takes bees but no capped brood. The mites that go with the swarm are the phoretic mites riding on the adult bees, because the capped brood, which is where the majority of a hive's mite population lives and reproduces, stays with the parent colony.
During swarming, the departing bees have often been in a semi-clustering state for several days before leaving. Phoretic mites that would normally seek out brood cells to reproduce have had fewer opportunities. Some researchers also note that the clustering and vibration behavior during swarming may dislodge some phoretic mites.
The net result is that a swarm leaves with roughly half to two-thirds fewer mites per bee than the parent colony had. If the parent colony was at 4%, the swarm might be at 2-2.5%. If the parent was at 1%, the swarm might come in under 0.5%.
But the swarm isn't starting from zero. And once you install it and brood rearing begins, the mite reproduction clock restarts immediately.
When to Do Your First Count on a Captured Swarm
Give the swarm about 2-3 weeks after installation to establish before you do an alcohol wash. By that point, the queen should be laying well, the bees have oriented to the new location, and the colony is past the most fragile establishment phase.
This first count is your baseline. It tells you what you're working with before mite populations build up through the season. A swarm that comes in at 0.5% needs a completely different monitoring plan than one that comes in at 1.8%.
If your baseline comes in above threshold (2% on an alcohol wash), treat even though the colony is newly installed. Early-season high counts don't improve on their own.
VarroaVault's swarm baseline count prompt triggers automatically when you log a new hive acquired via swarm capture. The platform asks you to schedule your first count at the 2-3 week mark and sets a reminder so you don't forget.
The Unknown Factor: The Parent Colony
If you caught a wild swarm or caught one from someone else's apiary, you don't know the mite history of the parent colony. You're working with incomplete information. A swarm that came from a highly infested parent colony may come in at 2-3% even after the broodless-swarm discount.
This is a stronger argument for doing the baseline count sooner rather than later. A swarm from an unknown source should be considered higher risk until the count proves otherwise.
Swarms from your own colonies are different. You know the parent colony's recent mite history. If the parent was at 1% last month, the swarm is probably around 0.5-0.8% and you can monitor with reasonable confidence.
Monitoring Through the First Season
After the baseline count, treat swarm colonies the same as any other colony for monitoring purposes. Monthly counts through spring and summer, more frequent monitoring in August (every 2-3 weeks), and a fall count before winter preparation.
The thing that catches beekeepers off guard is that a swarm can grow from a very small colony to a full-strength colony remarkably fast in summer. Mite populations grow with them. A swarm installed in May at 0.5% with rapid population growth can be at or above threshold by late July, not because of reinfestation, but because the mite population scaled with the colony.
Track all your swarm count history through VarroaVault's mite count tracking app so you can see how quickly counts are changing over the season. And before your first treatment with a new swarm colony, read through how to set up a varroa treatment program to make sure you're choosing the right method for the colony's current size and brood state.
Frequently Asked Questions
Do swarms have varroa mites?
Yes. Swarms are not mite-free, but they typically have 30-50% fewer mites per bee than the parent colony they came from. This is because the mites that reproduce in capped brood stay behind with the parent colony's brood frames when the swarm departs. The swarm takes only phoretic mites riding on adult bees. The lower starting load is helpful, but it's not zero, and once the swarm is installed and brood rearing begins, the mite population will grow. A baseline count 2-3 weeks after installation is the only way to know what you're actually dealing with.
When should I do my first mite count on a captured swarm?
Do your first alcohol wash at 2-3 weeks after installation. This gives the colony enough time to establish brood rearing and stabilize as a new hive, while still catching any high-mite situations before they compound. Log this first count as your baseline in your hive records. If the count comes in below 2%, continue on a monthly monitoring schedule. If it comes in above 2%, treat promptly regardless of how recently the swarm was installed.
How do I log a swarm acquisition in VarroaVault?
Create a new hive record in VarroaVault and select "swarm capture" as the acquisition type. Enter the capture date and any information you have about the source colony (your own colony ID if known, or note as "unknown wild swarm"). The platform automatically prompts you to schedule a baseline count at 2-3 weeks after capture, sets a monitoring reminder, and configures your threshold alerts. If you know the parent colony's recent mite count, you can add that as a note to help interpret the swarm's baseline when it comes in.
How do I know if my varroa treatment is working?
Run a mite count 2-4 weeks after the treatment ends and compare it to your pre-treatment count. The efficacy formula is: ((pre-count - post-count) / pre-count) x 100. A result above 90% indicates effective treatment. Results below 80% should trigger investigation for possible resistance, application error, or reinfestation. Log both counts in VarroaVault to track efficacy trends across treatment cycles.
How often should I check mite levels in my hives?
At minimum, once per month (every 3-4 weeks) during the active season. Increase to every 2 weeks when counts are near threshold or after a treatment to verify it worked. In fall, monitoring frequency matters most because the window to treat before winter bees are raised is narrow. VarroaVault's monitoring reminders can be set to your preferred interval for each apiary.
What records should I keep for varroa management?
Each record should include: date of count or treatment, hive identifier, monitoring method used, number of bees sampled, mites counted, infestation percentage, treatment product name and EPA registration number, dose applied, treatment start and end dates, and PHI end date. State apiarists typically expect this level of detail during inspections. VarroaVault captures all of these fields in a single log entry.
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
The information in this guide is most useful when you have your own mite count data to apply it to. VarroaVault stores every count, flags threshold crossings automatically, and builds the treatment history you need for state inspections and effective management decisions. Start your free trial at varroavault.com.