Chalkbrood vs. Healthy Brood Pattern

Chalkbrood is a fungal disease that kills honeybee larvae, but it’s rarely fatal to a colony and often clears on its own. Learning to spot the difference between healthy brood and chalkbrood-infected brood is one of the most practical skills you can develop as a beekeeper—it takes just a few inspections to train your eye.

What Healthy Brood Looks Like

Healthy brood appears as a tight, organized pattern of capped and uncapped cells filled with larvae or pupae. The uncapped cells (called “open brood”) contain white, C-shaped larvae that look like tiny grains of rice lying on their sides. These larvae should be glistening and moist, positioned consistently in the bottom curve of each cell.

Capped brood cells are sealed with a tan or light brown wax cap that sits slightly proud of the cell rim—not sunken in. The caps should look uniform across a patch of brood, though they may vary slightly in color depending on the bee race and pollen stores. A healthy brood pattern is tightly clustered with few or no empty cells scattered throughout; you might see the occasional empty cell, but large gaps in the pattern signal a problem.

The pattern itself should be relatively solid across multiple frames. Beekeepers often call this a “tight” or “solid” brood pattern. If you’re looking at a frame with brood on both sides, healthy brood will be present on most of the frame, not randomly scattered. The queen should be laying consistently enough that you see all stages—eggs (hard to spot without experience), young larvae, older larvae, and capped brood—all on the same frame.

What Chalkbrood-Affected Brood Looks Like

Chalkbrood-infected larvae die and mummify inside their cells, turning into hard, chalk-like mummies. These mummies are typically white, gray, or tan, though they can darken over time. The infected larva shrinks and hardens, eventually becoming a small, desiccated pellet that sits loose in the cell.

The most obvious sign is the presence of these visible mummies scattered throughout the brood pattern. They’re often easier to spot than you’d think—they stand out visually from healthy larvae and capped cells. Some mummies will be pushed out of cells by adult bees and found on the hive floor or the bottom board; these are sometimes called “chalkbrood mummies” or simply “mummies.”

Chalkbrood typically affects scattered cells rather than creating a completely diseased patch. You might see a few mummies on one frame, then none on the next. The disease is often worse in spring or early summer when conditions are cool and damp, and it tends to show up in clusters around the edges of the brood nest where it’s cooler.

You may also notice that some cells appear to have sunken or discolored caps—the bees sometimes try to cap over infected larvae, and the cap may look darker or dimpled compared to healthy capped brood. However, this isn’t always obvious, so don’t rely on it as your primary indicator.

Side-by-Side Comparison

The key difference: healthy brood looks organized and wet; chalkbrood looks like someone scattered small chalk pieces through the brood nest.

What to Do If You Spot Chalkbrood

First, don’t panic. Chalkbrood is not a reportable disease in many regions, but requirements vary—check with your local beekeeping association or agricultural authority to confirm the rules where you keep bees. Colonies often recover on their own within a few weeks or months. Be aware, however, that the spores of the causative fungus (Ascosphaera apis) are persistent and can be spread between colonies through shared equipment, robbing, or drifting bees, so good hygiene with your tools and frames matters.

Your main action is to improve hive conditions. Chalkbrood thrives in cool, damp environments, so ensure your hive has good ventilation and isn’t sitting in a perpetually shaded, wet spot. If your hive is in a low-lying area that collects moisture, consider moving it to higher ground or improving drainage around it. In spring, make sure the entrance isn’t blocked and that air can flow through the hive.

Remove any visible mummies from the bottom board (the floor of the hive) if you see them piling up, though this isn’t critical. The bees will handle most cleanup themselves through hygienic behavior—adult bees detect and remove infected material from the brood nest.

Do not treat chalkbrood with fungicides or antibiotics. There is no approved or effective chemical treatment, and it is unnecessary. Focus instead on keeping the hive dry and well-ventilated, which removes the conditions the fungus needs to thrive.

Monitor the hive over the next few inspections. The number of mummies should decrease as conditions improve and the colony’s population grows. If chalkbrood persists heavily into summer or the colony appears weak for other reasons, consider whether the hive location or queen quality might be the real issue.