American Foulbrood: Signs, Reporting, and What Happens Next

AFB is a disease of larvae, not adults. Adult bees are unharmed carriers: they clean out infected cells and spread spores through the hive on their mouthparts, in the food they share, and on the comb they walk over. A young larva swallows spores in its brood food, the spores germinate in its gut, the bacteria break through the gut wall, and the larva dies, usually after its cell is capped, at the late larval or prepupal stage. What is left liquefies into the brown gluey mass the rope test finds, then dries to a scale. Only the youngest larvae are readily infected, and it takes remarkably few spores to do it, which is the biological reason a low-level infection can smolder in a strong colony for a season before it becomes obvious.

The number that governs everything else is the spore count. A single dead larva can contain spores in the billions, and a frame of scale is a spore magazine. Those spores are not fragile: they tolerate desiccation, disinfectants, and ordinary heat, and remain infective in stored comb and honey for decades. That single property is why AFB gets a different rulebook from every other bee disease on this site. Chalkbrood and European foulbrood, covered in the EFB and chalkbrood guide, are managed with ventilation, requeening, and time. AFB is managed with fire, because there is no realistic way to disinfect drawn comb that has held it.

None of this makes AFB common. Most backyard keepers go a career without meeting it, and the state inspection systems that exist across the US are a large part of why. But it does make AFB the one disease where a beekeeper who guesses, hopes, or quietly moves equipment can seed an entire neighborhood. The correct posture is boring and effective: learn the signs, look at every brood frame you handle, and know the phone number of your state apiary program before you need it.

The pattern. Healthy capped brood is a dense, uniform slab. AFB brood is spotty, with capped cells scattered among opened and empty ones, because nurse bees uncap and try to remove infected larvae. Spotty brood by itself means very little: a failing queen produces it, chilled brood produces it, and so does the parasitic mite syndrome described in the virus guide. It is the flag that makes you look closer, not the diagnosis.

The cappings. This is where AFB starts to declare itself. Instead of dry, slightly convex, papery tan cappings, you see cappings that are sunken and concave, darker than their neighbors, moist or greasy in appearance, and pierced with small irregular holes chewed by workers. The combination of sunken, dark, and perforated on the same cell is the classic look.

The rope. Open a suspect cell and the remains are a brown to chocolate semi-fluid with no recognizable bee in it. Stir with a toothpick and draw out slowly, and AFB material follows in an elastic brown thread, commonly an inch or more, which then snaps and springs back. Nothing else in a bee hive ropes quite like that. European foulbrood larvae can be slightly pasty and watery but rarely rope more than a short distance, and sacbrood larvae lift out whole as a fluid-filled sac.

The smell. A strongly infected colony has an odor that veteran keepers recognize before they get the lid fully off: sour, penetrating, and most often described as a hot glue pot. Mild cases may not smell at all, so a clean-smelling hive proves nothing, but a glue-pot smell on a frame that also ropes is a diagnosis in all but name.

The scale. Late in the sequence, the dried remains form a hard, dark, brittle scale lying flat along the lower wall of the cell, sometimes with a fine upturned thread that is the dead pupa's tongue. AFB scale is stuck fast. You cannot flick it out with a toothpick without tearing the cell, and that adhesion is one of the most reliable field distinctions in brood disease work.

The rope test is the single most useful two-minute skill in brood disease diagnosis, and most beekeepers do it wrong by testing the wrong cell. You want a cell that was capped and has sunk, ideally one that has been partially chewed open by the bees, with brown material inside. A larva that is merely dead and white, or dried and crusty, will not rope no matter how healthy or sick the colony is, and testing three of those in a row produces false reassurance.

Use anything disposable: a toothpick, matchstick, dry grass stem, or the corner of a hive tool you are prepared to scorch afterward. Push it into the remains, stir once to load the tip, then withdraw slowly and steadily. A positive result stretches a brown, mucus-like thread that hangs together as you lift, usually 20 to 30 mm and sometimes much more. A negative test breaks immediately or produces a granular, watery, or crumbly mess. Do the test on at least three suspect cells before you draw a conclusion, and burn or bury the toothpick rather than dropping it in the grass by the hive.

A field rope is strong evidence, not a laboratory result. State apiary inspectors confirm suspect colonies in person, and diagnostic laboratory services for bee disease samples have long been available through state programs and federal bee research laboratories; check current availability and submission instructions with your state program and with USDA Agricultural Research Service. Confirmation matters, because the disposition it triggers, burning good equipment, is expensive enough to be worth getting right.

Four brood conditions account for nearly every "is this foulbrood?" photograph posted to a club forum. The table separates them on the signs you can actually see in the yard. The full workups for the others live in the EFB and chalkbrood guide and the virus guide.

Two of those rows do most of the work. If the remains rope a long brown thread, think AFB. If the scale lifts out of the cell in one piece, it is not AFB. Everything else is supporting evidence.

Understand the spores and every strange rule about AFB becomes obvious. Vegetative bacteria are easy to kill. Spores are a survival state, and Paenibacillus larvae spores tolerate drying, cold, most disinfectants, and considerable heat, staying infective in comb, honey, and hive parts for decades. Extension bee health programs, including eXtension bee health and the University of Minnesota bee health program, use that same decades framing, and it is the reason the disposition is destruction rather than cleaning.

Three practical consequences follow. First, drawn comb from an infected colony is permanently contaminated, and drawn comb is the most valuable thing a beekeeper owns, which is exactly what makes AFB so expensive. Second, honey can carry spores, which is why feeding honey of unknown origin back to bees is a hard no across every extension program that addresses it, and why honey from a suspect colony must never go on another hive. Third, a hive body that once held AFB is suspect until it is treated, which is why states that allow salvage of woodenware specify how: scorching the interior surfaces with a torch until the wood chars lightly, or gamma irradiation where a commercial facility is available.

This is also the reason for the most repeated warning in this article: the used equipment on the local classifieds. A stack of deep boxes with drawn comb for forty dollars is either the best deal in beekeeping or the most expensive purchase you will ever make, and you cannot tell by looking, because scale in old comb does not announce itself. We wrote about that trade in the beehive kit buying mistakes guide, and AFB is the reason the rule there is absolute rather than cautious.

In many US states, AFB is a reportable disease. The apiary program in your state department of agriculture maintains an inspection service, and the statutory framework in most states requires beekeepers to report suspected AFB and gives the inspector authority to inspect, quarantine, and order destruction of infected material. Specifics differ state to state, including who must register hives and what the response timeline looks like, so treat this page as an instruction to find your own state's program rather than as a statement of your state's law. Our beekeeping laws by state overview is the starting point for locating yours, and your county extension office or state beekeeping association will have the inspector's number on hand.

New beekeepers hesitate to call, imagining fines and confiscation. That instinct gets the disease spread. In practice, state inspectors are the most useful free resource in beekeeping: they see more disease in a month than most keepers see in a lifetime, they confirm or rule out AFB on the spot, and in the far more common case where the frame is actually chilled brood or EFB, they will tell you so and save you from burning perfectly good equipment. Where destruction is required, the inspector supervises it and documents it, which matters if you later sell nucs or move hives across a state line.

The other reason to call is that AFB is a neighborhood problem. Robbing bees strip a dying colony and carry contaminated honey home, exactly as they carry mites home in the fall reinvasion described in the varroa timing guide. An unreported AFB colony that collapses and gets robbed out can seed every apiary within flying range. Reporting is not an admission of bad beekeeping. It is the part of the job that protects everyone else's bees.

The standard resolution for a confirmed AFB colony in most US states is destruction by fire: the bees are killed, usually in the evening when the colony is home, and the combs and frames are burned in a pit, with the ashes buried. It is a grim procedure and it is not performative severity. It is the only method that reliably ends the spore load in drawn comb, and it is the same conclusion apiary programs around the world have reached independently.

The parts of the hive that are not wax get more options, subject to what your state allows. Scorching the interior of boxes, bottom boards, and covers with a propane torch until the surface chars is the traditional salvage method for woodenware. Gamma irradiation at a commercial facility is used where available and is the standard commercial approach in some regions, because it sterilizes assembled equipment including comb. Plastic and metal parts may be salvageable by scorching or approved chemical treatment. What is not on the menu anywhere: washing, sunning, freezing, or "letting it air out," none of which touch spores.

The economics are worth stating honestly, because they explain a lot of bad beekeeper behavior. A two-deep colony with drawn comb represents a few hundred dollars of equipment and a season of bee labor, and the temptation to quietly medicate and keep going is real. That path produces a colony that looks healthy, keeps producing spores, and then becomes a mite bomb equivalent for foulbrood when it eventually fails. The cost of doing it right once is far lower than the cost of seeding your own yard, and the cost of seeding your neighbor's is not yours to spend.

Antibiotics have a history in AFB management, and the important thing to understand is what they were ever doing. Antibacterial treatment suppresses the vegetative bacteria and clears the visible symptoms in a colony. It does not kill spores. The comb stays contaminated, the colony stays a reservoir, and when treatment stops the disease commonly returns. That is why extension guidance has long described antibiotics as symptom suppression rather than a cure, and why several apiary programs discourage or prohibit their use in AFB-positive colonies precisely because masking the disease makes surveillance impossible.

The regulatory picture is the second half. The antibiotics historically used in bee colonies are medically important antibiotics, and under current US rules their use in food-producing animals, honey bees included, requires veterinary oversight rather than over-the-counter purchase. In practice that means a veterinarian must be involved, through the mechanisms the FDA administers for veterinary feed directives and prescriptions. We deliberately publish no product names, no doses, and no timings for this, both because that information belongs on a label under a veterinarian's direction and because a beekeeper reaching for antibiotics before an inspector has seen the frame is usually about to make a reportable situation harder to resolve.

So the practical sequence for a suspect colony is unchanged by any of it: stop, isolate, report, confirm, follow the official disposition. If your state and your veterinarian have a role for antibacterial treatment in your situation, they will tell you. Nothing you buy on the internet is a shortcut around that conversation.

AFB prevention is unglamorous and close to complete, because the disease arrives by only a few routes.

Never buy or accept used drawn comb of unknown history. This is the rule that matters most. Estate-sale hives, marketplace stacks of "barely used" boxes with comb, and generous gifts from a keeper who quit are the classic entry point, and AFB scale in old comb is invisible to a buyer who does not know exactly what to look for. Used woodenware with no comb, scorched before use, is a defensible purchase. Used comb is not, at any price. We put this at the top of the buying mistakes guide for exactly this reason.

Never feed honey of unknown origin. Grocery store honey, a friend's honey, honey from a colony you did not inspect: all potential spore vehicles. Feed sugar syrup instead, mixed as described in the syrup feeding guide, and keep your own harvested honey for your own known-clean colonies.

Do not shuffle frames between colonies casually. Equalizing a weak hive with a frame of brood from a strong one is a normal management move and a normal disease-spreading move. Do it with colonies you have actually examined, and never from a colony with a brood pattern you cannot explain.

Inspect brood every time, and know what you are looking at. The habit of looking into cells rather than just counting frames is the whole game, and it is the core skill in the hive inspection guide. A copy of Beekeeping For Dummies ($15.99) next to the hive stand is a fair way to check your read against photographs before you panic or, worse, before you shrug.

Keep colonies strong and requeen unproductive stock. Hygienic behavior, the tendency of workers to detect and remove diseased brood, is heritable, and stock selected for it resists both foulbroods and chalkbrood better. Requeening a chronically weak colony from good stock is disease management, and the mechanics are in the requeening guide.

Because the response to AFB is drastic, the discipline of ruling it out matters. Here is the honest order of probability for a spotty, ugly brood frame in a US backyard hive.

Varroa and its viruses come first. Parasitic mite syndrome produces spotty brood, discolored larvae dying at odd stages, and a dwindling adult population, and it is far more common than either foulbrood. If you have not done an alcohol wash on the colony, you are missing the most likely explanation: the Mann Lake Varroa EasyCheck ($30.50) settles that question in five minutes, and the timing rules are in the varroa timing guide.

Chilled brood is second. A cold snap after a beekeeper spread the brood nest, or a colony too small for the space it is covering, produces dead brood in patches, often at the edges of the nest. It looks alarming and resolves itself.

Queen failure is third. A drone-laying queen or a laying worker produces a scattered, domed, unmistakably wrong pattern with no disease at all, and the fix is a new queen.

European foulbrood and chalkbrood are fourth and fifth, both covered in their own guide, and both usually managed rather than destroyed.

AFB comes after all of those in frequency, and before all of them in consequence. That is the whole reason to learn the rope test: it is a fast, cheap way to move a scary frame out of the AFB column, and on the rare day it does not, you have found the thing early enough to contain it.

1. Close the hive. Do not shake bees, do not pull more frames than you need, and do not start moving equipment around the yard.

2. Contain your tools and gloves. Scorch or wash the hive tool. Change or wash gloves. Do not open another colony with the same equipment until you have.

3. Reduce the entrance. A weak, dying colony gets robbed, and robbing is how AFB travels. Entrance reducers and robbing screens, covered in the robbing screen guide, buy you time until the inspector arrives.

4. Call the state apiary inspector and describe exactly what you saw: sunken perforated cappings, rope length, odor, scale adhesion. Follow their instructions on sampling or holding the colony.

5. Inspect the rest of the yard, carefully, in order. Work your other colonies with clean tools, strongest to weakest, looking at brood in every one. AFB in one hive is a strong reason to check every hive you own.

6. Carry out the disposition as directed, keep records of what was destroyed and when, and treat the woodenware question as the inspector rules on it.

7. Then do the boring part. Write down where every piece of equipment in that yard came from, and stop the practices that let unknown comb in. A confirmed AFB case is nearly always traceable to used equipment, fed honey, or a swapped frame, and the same route is still open until you close it.

You do not need to be afraid of AFB. You need to be literate in it. Learn the five signs, sunken and perforated cappings, brown gluey remains, a rope on the toothpick, glue-pot smell, and hard scale glued to the cell floor. Run the rope test whenever a brood frame looks wrong, which will mostly reassure you. Buy new comb, feed sugar rather than mystery honey, and keep a phone number for your state apiary program in the same note as your club's swarm line.

The rest of the disease library is built to be read alongside this page: European foulbrood and chalkbrood for the brood problems that are usually recoverable, nosema and dysentery for the adult-bee gut story that gets misdiagnosed every spring, bee viruses and deformed wing for the mite-driven half of colony health, and how to diagnose a deadout for the morning you open a hive that did not make it. Read together, they cover the questions that actually kill colonies, and AFB is the one where knowing the answer early is worth the most.