Introduction: European foulbrood (EFB) is one of the most common bacterial brood diseases found in honey bee colonies, especially during the spring buildup season. While some cases are mild, others can quickly weaken a hive if the symptoms are missed or mistaken for other brood issues. Recently, a beekeeper friend contacted me about a colony showing signs of unhealthy brood, so I went over to inspect the hive in person and learn more about what was happening inside the colony.

In this post, I’ll share photos I took from a hive that tested positive for European foulbrood, explain some of the common signs beekeepers should watch for, and discuss how to inspect your own hives for possible EFB symptoms. I’ll also go over a few treatment and management approaches that can help colonies recover and reduce the spread of the disease to other hives.

Because EFB can sometimes resemble other brood problems — including chilled brood, nutritional stress, or even early signs of more serious diseases — learning how to properly identify the symptoms is an important skill for any beekeeper. Hopefully these real-world examples and close-up images will help other beekeepers recognize potential warning signs early and make informed decisions in their own apiaries.

About: European foulbrood is a brew disease caused by bacteria Melissococcus plutonius. The bacterium competes with the larvae for food as the bacteria proliferates. The larval infection leads to mortality around 4-5 days old. EFB is associated with stressful conditions like sporadic nectar flows or an insufficient number of nurse bees to tend to brood. There are secondary bacteria associated with EFB that can lead to a variety of visual signs of the virus. EFB is contagious but unlike AFB, doesn’t produce spores. 

EFB normally strikes in late Spring-May & June-when colony populations are rapidly increasing. The llarva often  die before the pre-pupil stage that means they die young while they are still mobile in their cells, and that therefore creates a variety of twisted postures, the color can range from off-white to gray to black. If the larva are black, it is, you can often see the white respiratory tubes through their translucent skin.

The economic harm done to colonies because of EPB happens after the disease is cleared up. Since the infection causes a reduction to bee populations, it’s difficult for the colony to provide a surplus of honey. 

Signs:

• “C” shaped whitish-yellow to brown larvae, curled upward with a twisted appearance 
• Deflated larvae on the floor of a cell with a defined tracheal system 
• Scale is usually from brown to black, sunken to the floor of the cell 
• Visual signs are usually seen first around the perimeter of the brood nest 
• Moderate to severe infections result in a very spotty brood pattern that can be confused with a failing queen 

Sources: The Hive and the Honeybee by L.L. Langstroth and Diagnosis and Treatment of Common Honeybee Diseases-Second Edition-Bee Informed