There are pests, there are diseases, and then there is American Foulbrood — a scourge so virulent, so persistent, that in many jurisdictions it is legally reportable and the only sanctioned response is to burn everything. The hive, the frames, the bees, the honey — all of it must be destroyed, typically by fire, to prevent the disease from spreading to neighboring apiaries.
This is not alarmism. This is reality. American Foulbrood is the most serious bacterial disease your bees will ever face, and if you find it, your beekeeping year just took a very dark turn.
But knowledge is power. Let us learn to identify, understand, and — if fortune favors us — avoid this nightmare.
American Foulbrood (AFB) is caused by the spore-forming bacterium Paenibacillus larvae. The spores are nearly indestructible — they can survive for decades in soil, on equipment, in honey. A single spore, ingested by a bee larva, germinates in the gut and multiplies until the larva dies, liquefying from the inside.
The smell is the first clue. AFB-infected brood produces a foul, putrid odor — beekeepers describe it as like rotting fish or old gym socks. If you open a hive and are hit with a stench that makes you recoil, inspect the brood immediately.
The appearance is distinctive. Healthy capped brood has smooth, light-tan cappings, slightly convex. AFB-infected cappings are sunken, greasy-looking, and often perforated — the bees have tried to remove the dead larvae and punctured the caps in the process.
The ropy test is diagnostic. Insert a toothpick or twig into a suspect cell, stir gently, and slowly withdraw it. If the contents are healthy, they will come out as a solid larva or cleanly separated. If the contents stretch out in a long, coffee-colored, ropy strand that extends an inch or more from the cell, you have AFB. This is the signature of the disease — the liquefied, bacteria-filled remains of the larva.
The scale confirms it. Advanced AFB produces a hard, dark scale on the lower wall of the cell — the dried remnant of the dead larva, stuck fast and nearly impossible for the bees to remove. These scales are teeming with billions of spores. A single scale can infect an entire colony.
AFB is not curable. There is no treatment that eliminates the spores. Antibiotics like Terramycin can suppress symptoms temporarily, masking the disease, but the spores remain dormant in the hive, waiting. As soon as the antibiotic is withdrawn, the disease roars back.
Worse, AFB spreads like wildfire. Bees robbing an infected hive carry spores home. Beekeepers moving frames between colonies transfer spores. Even used equipment sold at a yard sale can harbor dormant spores. This is why burning is often the only legal option — incineration is the only method guaranteed to destroy the spores.
Check your local regulations. In many states, AFB is a reportable disease — you are required by law to notify the state apiary inspector if you find it. The inspector will confirm the diagnosis and advise you on approved disposal methods. Failure to report and destroy infected colonies can result in fines and the forced quarantine of your entire apiary.
"American Foulbrood does not forgive ignorance, and it does not respect property lines. If you find it, act swiftly and completely."
— State Apiary Inspector's Manual
European Foulbrood (EFB) is caused by a different bacterium, Melissococcus plutonius, and while unpleasant, it is far less catastrophic than AFB. EFB kills larvae before the cells are capped, and the larvae die in a twisted, off-white to yellow mass that does not produce the ropy consistency of AFB.
The smell is sour rather than putrid. The dead larvae are easier for the bees to remove. And crucially, EFB is often self-correcting. A strong nectar flow or a new, vigorous queen can allow the colony to bounce back without intervention.
If EFB persists, requeening is the standard response. A young, productive queen stimulates the workers to clean out infected brood more aggressively, breaking the disease cycle. Combine this with ensuring the colony has ample food, and EFB usually fades.
Unlike AFB, EFB does not require burning equipment. Frames can be cleaned, sterilized, and reused. But do not be complacent — EFB weakens colonies and makes them vulnerable to other threats.
Chalkbrood is caused by the fungus Ascosphaera apis and is visually striking. Infected larvae die and harden into white, chalky mummies that rattle around in the cells or get carried out by undertaker bees. You will find them on the bottom board or piled up at the hive entrance — small, mummy-like pellets, white or occasionally black if the fungus sporulates.
Chalkbrood is a stress disease. It appears when colonies are under environmental stress — cool, damp springs are prime time, as are periods of poor nutrition or overcrowding. The fungus spores are likely present in most hives but only cause problems when the bees' defenses are down.
There is no chemical treatment for chalkbrood, but there is a solution: reduce stress. Ensure good ventilation, reduce moisture, provide ample food, and consider requeening if the problem persists. Strong colonies from hygienic genetic lines often clean out chalkbrood on their own.
For all brood diseases, prevention follows the same playbook:
Do not panic, but do not delay. Contact your state apiary inspector immediately. Follow their guidance to the letter. If burning is required, do it at dusk when all bees are home, and dig a pit to contain the ashes. It is heartbreaking, but it protects every beekeeper within flight range of your hive.
If you have multiple hives, inspect them all. AFB may have spread. Disinfect yourself and your tools thoroughly between inspections. And take solace in this: you have learned something most beekeepers never face, and you are now far better equipped to prevent it in the future.