Colony health

European foulbrood

Updated October 2026

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The less serious of the two What it looks like Telling it from AFB, which is the whole point Why it appears What to do References

European foulbrood is the one people diagnose when they mean American foulbrood, and the one they dismiss when it is actually a sign the colony is under stress. It is less severe and it is not nothing.

The less serious of the two

eXtension describes AFB and EFB as two different but similar bacterial diseases of larvae and pupae, with EFB the less severe and the more common. Unlike AFB it is not usually a regulatory matter and it does not routinely end in burning equipment.

What it looks like

Larvae dying before capping, which is the key difference. You see them in open cells rather than under cappings.
Twisted, melted-looking larvae lying at odd angles instead of neatly curled.
Color shifting from pearly white to yellow to brown.
A sour smell rather than the glue-like smell of AFB.
A patchy brood pattern, because dead larvae are removed.

Telling it from AFB, which is the whole point

The rope test separates them. AFB-killed larvae draw out in a brown rope an inch or more. EFB does not rope the same way. And EFB kills before capping while AFB kills after, so the position of the dead larvae is itself a strong signal.

Field diagnostic kits for both are available from beekeeping suppliers at around $14 and eXtension describes them as easy and reasonably reliable. Given that one of the two is reportable and the other is not, that is a small amount of money to remove the doubt.

If there is any question at all, treat it as AFB until it is ruled out.

Why it appears

EFB often follows stress rather than causing it. A colony short of forage, chilled, overcrowded or struggling with a poor queen is the one that shows it, which is why it commonly appears in spring and commonly clears when conditions improve.

What to do

Improve the conditions that let it in. Requeening is a common and effective response, because it produces a brood break and often a better-laying queen. Feeding a colony short of stores helps.

Antibiotics exist for EFB and are veterinary-prescription in the United States, which is a conversation with a vet rather than a purchase. Contact your state inspector if you are unsure what you are looking at; that is what they are for.

References

eXtension Bee Health. European Foulbrood: A Bacterial Disease Affecting Honey Bee Brood; Diagnostic Kits for American and European Foulbrood. bee-health.extension.org

Michigan State University Extension. Guide on American and European foulbrood from the Honey Bee Health Coalition. canr.msu.edu

University of Georgia Extension. Honey Bees and Beekeeping (B1045). extension.uga.edu

American foulbrood is reportable in most states and European foulbrood generally is not, which is why confirming which one you have matters more than treating quickly. Your state apiary inspector is the authority.