Lesson 59: European Foulbrood
AFB's less deadly cousin: how to tell them apart, and how colonies recover
European foulbrood (EFB) is another bacterial disease of brood. It's found wherever honey bees are kept. It can look a lot like American foulbrood (lesson 58), but it's much less serious: the bacterium doesn't form long-lived spores, colonies often recover, and it can be treated. Telling the two apart is essential, because what you do is completely different.
What causes it
EFB is caused by the bacterium Melissococcus plutonius.
- Nurse bees feed contaminated food to very young larvae (under about a day old).
- The bacteria multiply in the larva's gut, competing with it for food. The larva becomes abnormally hungry and usually dies before its cell is capped, while still a coiled larva (unlike AFB, which kills after capping).
- Strong colonies can often control it: nurse bees remove the sick larvae, taking the bacteria with them. But bacteria can linger in cells and larval waste, so it can flare up again.
- EFB is often linked to stress: it's common after a strong honey flow in spring in some regions, when nurse bees are stretched thin.
The signs
- Larvae are twisted or corkscrewed in the cell, or curled upward, instead of lying in a neat "C".
- Discolored larvae: off-white, yellowish, grayish or brown, often with their breathing tubes (tracheae) visible as white lines through the skin.
- Larvae look melted, deflated, shrunken or rubbery.
- A spotty brood pattern, as dead larvae are removed.
- Sometimes sunken or perforated cappings, when some larvae die just after capping.
- Scale: if present, it's dark and rubbery, and comes out of the cell easily, unlike AFB's glued-down scale.
- Odor: often none, or mildly sour.
EFB vs. AFB at a glance
| European foulbrood | American foulbrood | |
|---|---|---|
| Cause | Melissococcus plutonius | Paenibacillus larvae |
| Long-lived spores? | No | Yes (decades) |
| When larvae die | Usually before capping, as coiled larvae | After capping, as prepupae or pupae |
| Dead larvae look | Twisted, yellow to brown, tracheae visible, melted or rubbery | Brown, melted, gooey, lying flat |
| Rope test | Doesn't rope (or only weakly) | Ropes out ½–1 inch or more |
| Scale | Rubbery, easily removed | Hard, stuck tight |
| Colony outcome | Often recovers | Usually dies |
| What to do | Watch, boost the colony, requeen; vet-prescribed antibiotics if needed | Destroy infected equipment; call the inspector |
Other things that look similar: chilled brood (lesson 67), sacbrood (lesson 60), and brood damaged by high varroa levels ("parasitic mite syndrome"; lesson 54). Chilled brood looks similar but doesn't pass a rope test, and high mite counts point to PMS. Colonies can have more than one brood problem at once. If you're unsure, have it checked: use a field test kit or ask a state inspector or extension specialist (lesson 58).
How it looks:
European foulbrood: larvae discolored, twisted and melted in their cells.
Healthy brood compared with AFB and EFB.
What to do about EFB
- Confirm it: visual signs, a negative rope test, a field test kit, or a lab sample. Some states require bacterial diseases to be reported; check with your state apiary program.
- Watch and wait if it's mild. Colonies often recover on their own, especially when a nectar flow starts. Note roughly how many cells are affected and check again.
- Help the colony get strong:
- Feed 1:1 syrup to simulate a nectar flow and stimulate brood rearing.
- Add a frame or two of healthy brood (from a healthy colony) to boost the nurse-bee population.
- Requeen the colony (lesson 45). A brood break while the new queen starts laying also interrupts the disease.
- In serious cases: the shook swarm method (shaking the bees onto new, clean equipment and destroying the old brood combs) breaks the cycle.
- Antibiotics (oxytetracycline) are available only with a veterinarian's order, and must follow the label exactly, never before a nectar flow. Specialists warn that antibiotics can keep sick larvae alive and prolong the problem, so they should be used carefully and not as a routine.
Sanitation matters for EFB too: clean tools between colonies, don't move frames from sick hives, and disinfect equipment (wash with soapy water, then soak in a 1:5 bleach solution) before reuse.
What to remember
- EFB kills larvae before capping; larvae are twisted, yellow-brown, melted, tracheae visible.
- No long-lived spores; colonies often recover, unlike AFB.
- Tell it from AFB: EFB doesn't rope and its scale is rubbery and loose.
- Fix: watch, feed 1:1, add healthy brood, requeen, shook swarm if severe; antibiotics only by vet order.
- When unsure, get it confirmed.
Quick check
- When does EFB usually kill a larva, compared with AFB?
- What does an EFB-infected larva typically look like?
- Name two ways to help a colony recover from EFB.
Show answers
1. EFB usually kills larvae before capping; AFB kills them after capping. 2. Twisted or curled in the cell, yellowish to brown, looking melted or rubbery, with breathing tubes visible. 3. Any two of: feeding 1:1 syrup to simulate a flow; adding frames of healthy brood; requeening; shook swarm in severe cases.
Adapted from: UF/IFAS Extension, Identification and Treatment of European Foulbrood (ENY174/IN1272); Honey Bee Health Coalition, Identifying and Mitigating Foulbrood in Honey Bee Colonies (2nd ed., 2022); UGA Bee Program, Honey Bee Disorders: Bacterial Diseases and Non-infectious Diseases and Pests; Penn State Extension, A Quick Reference Guide to Honey Bee Parasites, Pests, Predators, and Diseases.
Photo: EFB, Výzkumný ústav včelařský, CC BY-SA 4.0 (via Wikimedia Commons). Diagram: Forge Guides.
Adapted from university Extension sources. Experienced Georgia beekeepers are reviewing these lessons. See something that doesn't match your experience? Tell us.