Deformed Wing Virus in Honey Bees: What It Is, What Causes It, and How to Stop It
You open the hive and there they are: bees with shriveled, crumpled wings, crawling on the frames or stumbling around on the landing board, unable to fly. That is deformed wing virus (DWV), and it is the most visible warning sign a colony can give you. It is also, in nearly every case, not really a virus problem. It is a mite problem wearing a virus costume.
The short version
Deformed wing virus is spread almost entirely by varroa mites. Bees with deformed wings mean your mite load is already high. There is no treatment for the virus itself; you treat the mites, and the virus fades with them. Do a mite wash today and treat if the count is over 3 per 100 bees.
What Deformed Wing Virus Actually Is
DWV is an RNA virus that has been in honey bees for a long time. Before varroa arrived, it was mostly harmless: bees carried it at low levels, passed it through food and mating, and almost never showed symptoms. What changed everything was the mite.
When a varroa mite feeds on a developing pupa, it injects the virus straight into the bee's body, bypassing every defense the bee has. Viral loads in mite-infested bees can run thousands of times higher than in bees that only picked the virus up orally. A bee that gets a heavy dose as a pupa emerges with the classic symptoms: stunted or crumpled wings, a shortened abdomen, discoloration, and a lifespan measured in days instead of weeks.
The bees you can see with bad wings are only the worst cases. For every crawler on the landing board, there are many more bees in the hive carrying high viral loads with normal-looking wings, and they are sick too. A 2025 study in Scientific Reports (Ferreira et al.) found that DWV-infected workers start foraging too early, bring back nectar only half as often as healthy bees (8% vs. 17% of trips), and the nectar they do bring back has far less sugar in it. The colony starves slowly while looking full.
Two Strains, and the Nastier One Is Winning
There are two main genotypes, DWV-A and DWV-B. DWV-B (sometimes called Varroa destructor virus-1) replicates inside the mite itself, which makes it a far more efficient traveler. A 2025 survey of 116 colonies across 15 European countries found DWV-B present in 82% of samples from mite-infested regions, with viral loads more than ten times higher than DWV-A, and it has been linked to overwinter worker loss in multiple studies. The same survey found that colonies treated for mites carried dramatically lower viral loads than untreated ones, and that viral load tracked mite infestation closely.
In the US, this stopped being an academic distinction in 2025. USDA-ARS researchers investigating the collapse of more than 60% of commercial colonies since summer 2024, roughly 1.7 million hives, found DWV-A, DWV-B and acute bee paralysis virus in the dead-outs, and found amitraz resistance in virtually every mite they collected. The mites were not being controlled, and the viruses did the rest.
How to Recognize It
| What you see | What it means |
|---|---|
| Bees with crumpled, stubby or missing wings | Classic DWV. Those bees were parasitized as pupae. |
| Bees crawling on the ground in front of the hive, unable to fly | DWV, sometimes with paralysis viruses that travel with it. |
| Bees with shortened, bloated or discolored abdomens | Heavy viral load, usually alongside wing symptoms. |
| Spotty brood, sunken or chewed cappings, pupae pulled out | Parasitic mite syndrome: mites plus viruses hitting the brood. |
| Mites visible on adult bees or in drone brood | You are past the point of asking whether to treat. |
One important point: if you can see deformed wings, the colony's mite level is already high, typically well over the 3-per-100 treatment threshold. Wing damage is not an early warning. The early warning is a mite wash.
How to Stop It
There is no medication for deformed wing virus. Nothing you can buy kills the virus inside a bee. What you can do is remove the thing that is injecting it, and when mite loads drop, viral loads follow within a brood cycle or two as the sick bees die off and healthy bees emerge in their place.
Step 1: count. Do an alcohol wash on a representative colony with the Easy-Check. Half a cup of nurse bees, 300 or so, from a brood frame. Over 3 mites per 100 bees in summer, treat now. Over 1 per 100 in winter, same.
Step 2: treat with something the mites aren't resistant to. The USDA finding on amitraz resistance is the reason so many beekeepers have moved to oxalic acid: mites have never developed resistance to it, it works with honey supers on, and it costs cents per hive. With brood present, that means repeated vaporization across the brood cycle; our dosage and schedule guide lays out exactly how many rounds and how far apart.
Step 3: count again. Two to three weeks after your last treatment, wash again. You want the number near zero. If you still see crawlers, that is the last of the bees that were already parasitized as pupae; they will be gone within a couple of weeks, and the bees emerging behind them will be clean.
Step 4: protect the winter bees. The bees raised in late summer and fall are the ones that have to live for months. If they emerge carrying a high DWV load, the colony dies in January regardless of how many bees went into winter. Get your mite count down before the winter bees are raised, not after.
Why Waiting Doesn't Work
A colony with visible DWV can look busy and populous right up until it collapses, because the sick bees are still there, just not doing their jobs. A 2019 Cornell study (Peck and Seeley) showed what happens next: as the colony weakens it becomes a target for robbing, and the robbers carry the mites, and the virus, home to every hive within at least 300 meters. Your DWV problem becomes your neighbor's problem, and theirs becomes yours. Treating early is how you keep the whole bee yard clean.
Tools We Use (and Recommend)
- InstantVap Oxalic Acid Vaporizer: cordless, fast, and the way we keep DWV out of our own yards. See all InstantVap models. Lorob Bees is the primary US seller, with stateside customer service and warranty.
- Oxalic Acid: EPA-registered EZ-OX. No known mite resistance.
- Mite Monitoring: the Easy-Check mite wash. The count is the only early warning you get.
- PPE: a full-face respirator rated for acid vapor, plus gloves.
Not sure whether what you're seeing is mites at all? Start with what varroa mites look like and how they live, then learn how to do a mite wash.
Happy Beekeeping from the Lorob Bees Team
Keep reading: Explore all Lorob Bees beekeeping guides — varroa, oxalic acid vaporization, pests and diseases, all in one place.
Sources
- USDA Agricultural Research Service, Viruses from miticide-resistant parasitic mites are cause of recent honey bee colony collapses, June 2025
- Sircoulomb F. et al., Genotype B of deformed wing virus and related recombinant viruses become dominant in European honey bee colonies, Scientific Reports, 2025
- Ferreira H. et al., Deformed wing virus affects foraging success and foraging specialization of honeybee workers, Scientific Reports, 2025
- Peck D.T. and Seeley T.D., Mite bombs or robber lures? The roles of drifting and robbing in Varroa destructor transmission from collapsing honey bee colonies to their neighbors, PLOS ONE, 2019
- Honey Bee Health Coalition, Tools for Varroa Management, 8th ed.
General beekeeping information, not a substitute for the product label. Always read and follow the label of the EPA-registered oxalic acid product you use.
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