75. What is chalkbrood?

Chalkbrood is a common fungal disease that affects honeybee larvae. It is usually not as serious as some other bee diseases, but it is a clear sign that your colony may be under stress.

For beginners, chalkbrood is often one of the first problems you might notice. The good news is that it is manageable and often reversible with simple changes.

What causes chalkbrood?

Chalkbrood is caused by a fungus called Ascosphaera apis. The spores of this fungus are commonly present in many hives, but they usually only cause problems when conditions favour their growth.

The disease tends to appear when the hive environment becomes cool, damp, or poorly ventilated. Weak colonies are especially vulnerable because they struggle to keep the brood warm and dry.

How does it affect the bees?

Chalkbrood affects developing larvae inside the brood cells.

When a larva becomes infected, the fungus grows inside its body. Eventually, the larva dies and turns into a hard, chalk-like shape known as a “mummy.”

These mummies are often:

• White at first

• Later turning grey or black

• Light and dry, almost like a small piece of chalk

Worker bees usually remove these mummies and drop them outside the hive, so you may notice them near the entrance.

Signs to look for

Chalkbrood is relatively easy to recognise once you know what to look for.

Common signs include:

• White or black mummified larvae in the cells

• A patchy brood pattern

• Chalky debris at or near the hive entrance

Unlike more serious diseases, chalkbrood does not usually have a strong smell.

Why does chalkbrood happen?

Chalkbrood is often linked to stress in the colony.

This can include:

• Cool or wet weather

• Poor ventilation inside the hive

• A weak or ageing queen

• A small population that cannot maintain brood warmth

In many cases, the disease appears during spring when temperatures are still fluctuating.

How can you manage it?

The key to managing chalkbrood is to improve the overall health and environment of the hive.

Here are some simple steps:

• Increase sunlight exposure

  
  

  Place the hive where it receives good morning sun.

• Improve ventilation

  
  

  Ensure the hive is dry and well-aired.

• Strengthen the colony

  
  

  A strong population can better control the brood environment.

• Replace the queen if needed

  
  

  A healthy, productive queen can make a noticeable difference.

A reassuring perspective

Chalkbrood can look worrying at first, especially when you see those white mummies in the hive. But in most cases, it is not a disaster.

With a few practical adjustments and a bit of patience, many colonies recover well on their own.

Think of chalkbrood as a gentle reminder from your bees—a signal to improve their living conditions. Once you respond, your colony will often bounce back and continue to thrive.