Last updated: August 21, 2026
American foulbrood is the one disease that changes how a beekeeper thinks about their equipment. Most hive problems are about this season: mites, a failing queen, a poor flow. AFB is about the boxes themselves, because the spores survive in wax and woodenware for decades and they do not care that the colony that made them is long gone.
It is also a reportable disease in most states, which means the decision about what happens next is not yours alone. This article is about recognizing it in your own hive and knowing who to call. It deliberately contains no treatment protocol, because writing one would be the wrong thing for a website to do and because your state apiarist gives better advice than any article can.
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Quick Answer
How do you recognize American foulbrood, and what then?
- Look for a patchy, spotty brood pattern with sunken, greasy, perforated cappings rather than clean domed ones.
- The classic field sign is ropiness: dead larval remains draw out in a thread when probed with a matchstick.
- Old infections leave a hard dark scale stuck along the lower cell wall that cannot be scraped out.
- AFB is reportable in most states. Stop moving frames and equipment, and contact your state apiarist before you do anything else.
Bottom line: your job is to recognize it early, quarantine the hive, and call the state. What happens next is directed by them.
What AFB Is and Why It Is Different
American foulbrood is a bacterial disease of honey bee larvae caused by Paenibacillus larvae. Young larvae ingest spores in their food, the bacteria multiply inside them, and the larva dies after the cell is capped. What is left behind is not a dead grub but a spore factory, and a single infected cell can hold an enormous number of them.
The spores are the reason this disease sits in a category of its own. They tolerate heat, drying and time, and they persist in comb, in propolis and in the wood of the box. A hive that dies of AFB and is stored in the shed is a loaded trap for whatever colony gets those boxes next, which is exactly how it spreads between backyard apiaries.
How It Travels
Two routes matter to a backyard keeper. Robbing, when bees from a healthy hive strip a dying one and carry contaminated honey home, and beekeepers, when frames, hive tools or secondhand equipment move between colonies. The second route is the one you control, and it is the argument for buying new woodenware rather than a bargain lot from a stranger.
What It Looks Like in the Brood Nest
Healthy capped brood looks like a solid slab of evenly domed, dry, tan cappings. AFB brood looks wrong before you can say why: the pattern goes patchy with scattered empty cells, and the cappings that remain are darker, sunken inward, moist looking and often pierced with small ragged holes where bees have tried to remove what is inside.
Open one of those cells and the contents are not a recognizable larva. Early on there is a coffee-colored, melted-looking mass. Later it dries into a dark scale that lies flat along the lower wall of the cell and adheres so firmly that scraping does not lift it. That scale is what makes old equipment dangerous years later.
The Ropiness Check
The field test beekeepers are taught is simple. Push a matchstick or a twig into a suspect cell, stir, and withdraw it slowly. Remains that draw out in a brown, elastic thread rather than breaking cleanly are the classic sign. It is a strong indicator, not a laboratory result, and the next step after a positive is a phone call rather than a decision.
The Smell
Beekeepers describe an AFB hive as smelling sour, like a glue pot or old animal hide. It is real, and experienced inspectors do notice it, but a smell alone proves nothing. Plenty of stressed hives smell odd, and a dead colony that has been robbed out and rained on smells worse than either.
Telling It From European Foulbrood
European foulbrood is a different bacterium with a different course, and it is often confused with AFB by newer keepers. EFB usually kills larvae before capping, so you see twisted, discolored larvae in open cells rather than sunken cappings, and the remains do not rope out the way AFB remains do.
The reason the distinction matters is that the responses differ, and neither response should be improvised. Both are reportable in many states. If you cannot tell which you are looking at, that uncertainty is not a problem to solve on the internet, it is the reason to get an inspector to look.
| Sign | American foulbrood | European foulbrood | Easily confused with |
|---|---|---|---|
| When larvae die | After the cell is capped | Usually before capping | Chilled brood, poor nutrition |
| Cappings | Sunken, greasy, perforated | Mostly open cells affected | Spotty pattern from a failing queen |
| Ropiness test | Draws into an elastic thread | Does not rope | Watery decomposition in old deadouts |
| Residue | Hard dark scale, firmly attached | Rubbery remains, removable | Pollen packed into empty cells |
What to Do the Moment You Suspect It
Close the hive. Do not pull frames from it into other colonies, do not swap boxes, do not put a suspect frame in the truck bed with clean gear, and do not feed honey from that hive to anything. Scrape and clean your hive tool and gloves before you touch another colony, and consider ending the inspection round there for the day.
Then contact your state apiarist. Every state has one, usually through the department of agriculture, and inspections for suspected foulbrood are part of the job they exist to do. They will confirm or rule it out, and they will tell you what your state requires. In many states the response is directed rather than optional, and it can involve destroying equipment.
Why You Should Not Improvise
There is a lot of advice online about antibiotics, irradiation, scorching boxes and salvaging frames, and some of it is even accurate somewhere. It is not a decision to make from a search result. Antibiotic use in hives is regulated and requires veterinary involvement in the United States, and the choice between salvage and destruction depends on your state’s rules and on how far the infection has gone.
Reducing the Odds in the First Place
You cannot make an apiary immune, but backyard keepers do have real levers. Buy new woodenware rather than used boxes of unknown history, do not accept donated frames of drawn comb from someone you cannot ask about disease history, and keep hive tools clean between colonies rather than between apiaries.
Beyond that, the general rule holds: strong colonies with room to work and a manageable mite load deal with problems that overwhelm weak ones. Getting the basics right from the start is what our guide to the beekeeping starter kit is about, and a good smoker is part of running calm, quick inspections that let you actually look at brood pattern rather than fighting the bees.
Look at Brood Every Time
Nearly every AFB case caught early was caught by somebody who habitually looked at capped brood instead of just confirming eggs and closing up. Two minutes of looking at the pattern in the middle frames is the single most valuable habit in beekeeping. Our hive inspection checklist puts it in order.
Frequently Asked Questions
Is American foulbrood reportable? In most states, yes. The specific requirement varies, which is why the reliable action is to contact your state apiarist through your department of agriculture as soon as you suspect it, before moving any equipment.
Can AFB spread to my other hives? Yes, mainly through robbing and through beekeepers moving frames, tools and boxes between colonies. Stopping both routes the moment you suspect it is the most useful thing you can do.
Can I save the equipment? That depends on your state’s rules and on the extent of the infection, and it is a question for the inspector who looks at your hive. Spores persist in wax and wood for a very long time, which is why the answer is often no.
Is honey from an AFB hive dangerous to people? AFB affects bee larvae, not people. The reason not to harvest or share it is that the honey carries spores that will infect other colonies, including through a jar left open outdoors.
Are there test kits? Field lateral-flow kits exist and are used by inspectors and associations, and a positive result still leads to the same phone call. The USDA Bee Research Laboratory in Beltsville also accepts samples for diagnosis, which your state apiarist can point you to.
How is it different from a hive that simply died? A plain deadout does not leave hard scale adhered to cell walls or ropey remains under sunken cappings. If you are working through a dead colony and are not sure what you are seeing, our guide to reading a deadout covers the alternatives.
The Bottom Line
American foulbrood is worth learning to recognize precisely because it is rare enough that most backyard keepers never see it, and serious enough that missing it costs an apiary rather than a colony. Learn the sunken perforated cappings, the ropiness check and the hard scale, keep tools clean between hives, and buy new woodenware rather than mystery boxes. If you suspect it, close the hive and call your state apiarist rather than acting on anything you read online, including here. Next, read reading a hive that did not make it and chalkbrood and nosema for the problems more likely to be behind what you are seeing.