European Foulbrood

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Healthy honey bee colonies are the desire of all beekeepers. Yet, we facing many challenges in the struggle to keep our hives productive. One adversary is European Foulbrood (EFB). A bacterial disease caused by Melissococcus plutonius poses a serious threat to honey bee larvae. The loss of the next generation of workers can have devastating effects on colony strength.

Beekeeper inspecting frame from hive that may have European Foulbrood.

Here are some facts that beekeepers should know about when dealing with an outbreak of European Foulbrood. By understanding the problem, you are better able to protect your apiary from this honey bee disease.

Understanding European Foulbrood Disease

European Foulbrood (EFB) can be a challenge for any colony of honey bees. Beekeepers need to know what causes it and how it affects the hive.

This bacteria harms the developing young bees in the hive – called brood. (The term “bee brood” represents all stages of larval growth and the pupa. We usually throw bee eggs in there too).

EFB targets honey bee larvae. The life cycle of the pathogen is directly tied to the brood rearing activities of the hive. Infected nurse bees, feed growing larvae – infecting the delicate brood with the disease.

The bacterium affects the gut of bee larvae and interferes with their development. Unlike its notorious counterpart – American Foulbrood (AFB), European Foulbrood does not form long-lasting spores that can infect equipment for years.

Understanding the difference between these two foulbrood diseases is essential for accurate diagnosis and treatment options.

EFB Symptoms

While adult bees can carry the disease, it is the bee brood that are affected. So, this is where we look for signs of the disease. It is common discovered during routine hive inspections.

Recognizing the symptoms of European Foulbrood allows for early intervention before the overall health of the hive declines.

  • irregular brood pattern
  • discolored larvae
  • sour odor

Irregular Brood Pattern

Evaluate the brood pattern of the hive is a “must do” for any hive inspection. Normally capped brood will appear in a compact, uniform pattern with few empty cells.

EFB-infected colonies often exhibit an irregular pattern of capped brood with cells scattered here and there. This indicates the disease’s affect on normal brood development resulting in the death of young before being capped.

Healthy white bee larvae in comb.

Discoloration of Larvae

Healthy bee larvae are white and shiny. Anytime you see, brown, yellow or dark larvae – there is a problem.

Because they generally die before the wax cap is added, the dying larva may twist in the cell. They may appear deflated with parts of the trachea system easily visible.

An area of young larva, yellow or brown in color and twisted in the wax cell is the most obvious sign of the disease. 

The dead may have a slight ropiness when the contents of the cell is pulled out – but not to the level of AFB.

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In general, a honey bee hive has a pleasant odor. (Well, except for the time of year when the bees are working goldenrod flowers – they stink!).

An unpleasant scent or sour smell in the hive is another indicator of European Foulbrood infection. Honestly, in my experience, all dead brood stinks. But your olfactory sense may be more acute than mine.

Impact on Colonies

European Foulbrood is not necessarily a death sentence for the colony in the same way that American Foulbrood can be.

Rather it is a stress disease, that only seems to show up in adverse conditions. A strong colony may control the disease all on their own with no assistance from a beekeeper or apiarist

However, the disruption to brood rearing can result in hives with low populations. Honey production may be affected and the colony is overall less healthy.

Too few bees in a colony opens the doors for problems with robbing bees, various pests and the possibility of not storing enough food for Winter.

How is it Spread

While EFB can occur at any time, it is more common in mid- late Spring. The bacterium that causes EFB overwinters inside the colony. 

The bacteria remains viable in a vegetative state for up to 3 years. However, it only causes problems when it becomes active and begins to multiply.

It can be found in the cell walls of comb, in feces and even on the wax debris found on your bottom board. You can find a lot of gnarly things down there including wax moth larvae and Small Hive Beetles. A good reason to clean the hive bottom board periodically.

Feeding young is a constant job with thousands of trips being made to each brood cell. Alas, this life-giving food may also contain the bacterium that causes European Foulbrood

Tiny bee larvae are eating machines-the only thing they do is eat and grow. When the bacteria reached the mid-gut it multiplies competing with the young for food. This causes the larvae to become ravenous and needing more and more food. 

Sometimes, the nurse bees recognize when a larva is “not behaving normal”. They may decide that something is wrong and remove the infected from the hive. Otherwise, the young bees starve from lack of nutrition.

In addition to spreading within the hive by nurse bees, it also spreads from hive to hive. Swarms, drifting bees that go from one hive to another (common with drones) and even absconding colonies take the bacteria with them.

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Nurse bees in hive feeding larvae.

European Foulbrood Treatments

Sometimes EFB clears up on its own when colony conditions improve. In some apiaries, a honey flow with fresh nectar coming in clears the problem up quickly.

However, if the hive is affected to the point that you need to take action, there are some steps to take that can help the bees.

  • requeen the colony
  • break the brood cycle
  • chemical treatment – antibiotics

New Queen

Requeening the colony can help with EFB on two fronts. First, some “strains – breeds” of honey bees have a bit more resistance to the bacterium.

And, maybe a new queen will produce daughters that have the hygienic trait of removing infected larvae faster.

Break in Brood Cycle

Another way to help is to create a break in the brood cycle. (Of course, introducing a new queen does this too. There will be a delay in new brood while the queen is being released from her cage.)

In a light infection, a break in the cycle gives the nurse bees time to clean out the diseased young. This results in less active bacterium in the hive.


The last option is chemical treatment with antibiotics. In recent years, many beekeepers have moved away from using antibiotics for EFB.

However, “oxytetracycline HCL” sold as Terramycin is labeled for treatment of European Foulbrood in hives. This powder is mixed with sugar or sugar water and fed to the colonies.

At this time, a VFD (Veterinary Feed Directive) is needed to purchase Terramycin. This means you need a veterinarian – for your bees prescription 🙂


Are any strains of honey bees immune to European Foulbrood?

No strain of honey bees is immune to European Foulbrood but some do show a bit more resistance.

Are all types of honey bee larvae susceptible to EFB?

Yes, the larvae of workers, drones and developing queens may be infected with European Foulbrood.

How dangerous is European Foulbrood?

In most cases, EFB does not kill a colony but it can reduce the population to a point that the hive fails. Monitor any outbreak and be ready to assist when needed.

What should beekeepers do if they suspect European Foulbrood in their colonies?

It is important to rule out an infection of American Foulbrood as it can have similar symptoms that are difficult for a novice to distinguish. Reach out to the state bee inspector, a local beekeeping association or get a AFB field kit to rule it out.

How do you get rid of European Foulbrood?

Strong colonies often recover on their own from a light case of European Foulbrood. Other options include, requeening the hive, causing a break in the brood cycle or using a chemical treatment.

Final Thoughts

It is not always easy to diagnose problems affecting the hives. Symptoms for conditions such as varroa infestations, nosema disease and others are often similar to one another. Yet, by understanding diseases and recognizing early symptoms, you can help your bees win the battle against pathogens such as EFB.

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