Definition
What is foulbrood? Foulbrood refers to two distinct bacterial diseases of honey bee brood: American Foulbrood (AFB) caused by Paenibacillus larvae, and European Foulbrood (EFB) caused by Melissococcus plutonius. Both kill developing larvae but differ critically in severity, treatment, and legal implications.
Why This Matters More Than Most Hive Problems
AFB is legally notifiable in most US states. In severe cases equipment must be burned by law. AFB spores survive 80+ years in wood and wax. A single infected hive can spread to neighboring apiaries through robbing bees — making early identification critical for your entire local beekeeping community, not just your own hive.
American Foulbrood (AFB): Identification Guide
Visual Signs
- Cappings: sunken, dark brown, greasy-looking, sometimes with small holes
- Larvae: dark brown sludge filling the cell base — no longer recognizable as a larva
- Smell: foul, rotten — similar to rotting meat or dried glue
Definitive Field Test — The Matchstick Test
Insert a twig or matchstick into a suspicious dark cell, stir gently, withdraw slowly. Positive AFB: contents pull into a sticky 2–3cm ropy thread before snapping. This is the definitive diagnosis test.
Severity: CRITICAL
Do not move any equipment. Close the hive. Contact your state department of agriculture apiarist immediately.
If you suspect AFB — stop, close the hive, and call your state apiarist before doing anything else. Moving infected equipment is how AFB spreads between apiaries.
European Foulbrood (EFB): Identification Guide
Visual Signs
- Larvae: yellow to brown, melted, twisted in cells — die before capping, so mostly uncapped
- Cappings: mostly normal — distinguish from AFB by looking at the larvae themselves
- Smell: sour or vinegary — unpleasant but not the rotten-meat smell of AFB
Matchstick test result: NEGATIVE — EFB larvae do not pull into a ropy thread.
Cause: stress disease — outbreaks linked to poor forage, chilling, overcrowding, or nutritional stress.
Severity: MODERATE
Most colonies recover if the stress cause is addressed. Treatment: Terramycin (oxytetracycline) prescribed by a licensed vet under Veterinary Feed Directive.
AFB vs EFB Quick-Reference Table
| Feature | American Foulbrood | European Foulbrood |
|---|---|---|
| Larvae affected | Capped (older) | Uncapped (young) |
| Cell cap | Sunken, dark, perforated | Usually normal |
| Larval color | Dark brown sludge | Yellow to brown |
| Smell | Foul, rotten | Sour, vinegary |
| Matchstick test | Positive — ropy thread | Negative |
| Spore survival | 80+ years | Much shorter |
| Legal status | Notifiable in most states | Reportable in some |
| Treatment | None — burn | Terramycin + reduce stress |
How to Perform the Matchstick Test Safely
Select a capped frame
Choose a capped frame with sunken or discolored caps.
Pierce a suspicious cap
Pierce a suspicious cap with a matchstick or twig.
Stir gently inside the cell
Stir gently inside the cell.
Withdraw slowly while watching
Positive AFB: contents stretch 2–3cm in a ropy brown thread. Negative: liquid, possibly smelly, but no thread.
After testing: burn the matchstick immediately. Wash hands before touching any other equipment. AFB spores contaminate surfaces and clothing.
FAQs
AFB is present in every US state. Ask your local beekeeping club — annual free hive inspections by your state apiarist are the best early detection system.
No — there is no approved effective treatment. Terramycin previously used shows significant resistance. Burning is legally required in most states. Self-treatment spreads resistant strains.
A free visit to inspect frames, send suspicious samples to a lab, and provide a diagnosis. In most states they are a resource, not an enforcement officer — contact them early without fear.
Never feed honey from unknown sources, sterilize tools between hives, replace frames every 3–5 years, and never buy used woodenware without disease history documentation.