Chalkbrood disease of honey bees

Chalkbrood is a fungal disease of honey bee brood that infects the gut of the larvae. It is caused by a spore-forming fungus named Ascosphaera apis that is consumed along with larval food.  Although chalkbrood disease can affect workers, drones, or queens it most often occurs in workers and drones.

Chalkbrood is frequently seen in late spring when colonies are expanding rapidly, the weather is still cool, and there may not be enough nurse bees to keep the brood warm. It often disappears spontaneously as summer temperatures rise. Although chalkbrood rarely destroys a colony, it can weaken a colony and cause reduced honey production.

What does chalkbrood disease look like?

  • Larvae become chalk-white and are often covered with cottony filaments
  • The white coloration may eventually give way to a gray or black, depending on the life stage of the fungus
  • It often appears at the perimeter of the brood nest
  • Infected or dead larvae may be seen at the hive entrance or in pollen traps. The dead and hardened larvae are referred to as “mummies.”

How does the disease enter the hive?

  • The disease is transmitted by spores that are readily moved from colony to colony on infected pollen, robbing bees, drifting bees, or beekeeping equipment.
  • Since spores remain viable for many years, they can persist in a hive until the conditions become right for growing.

What conditions allow the chalkbrood fungus to grow?

  • Excessive moisture in the hive, caused by poor ventilation
  • Cool temperatures
  • Inadequate colony nutrition (a healthy colony is more apt to keep the hive free of mummies and keep the brood nest warm)
  • Colonies weakened by other disease organisms
  • Poor genetic resistance

How can chalkbrood be prevented or reduced?

  • Replace old, blackened brood combs as these may harbor chalkbrood spores
  • If a colony lacks sufficient food stores, supplement with good-quality feed
  • Replace queens with stock bread for hygienic behavior and/or disease resistance

Some reports have indicated that the incidence of chalkbrood disease is increasing. The increased frequency may be related to poor nutrition, higher disease loads, and increased colony stress that seems to be occurring in honey bees around the globe.

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  • How should I handle my hive having chalk brood disease? I am a second year beekeeper and have 4 hives. I am worried that my other hives will get this. Ugh. The hive we had last year died, MN winter. I did reuse the frames from that hive in my 4 hives this year. Help

    • Becky,

      Colonies where the brood got chilled are most likely to come down with chalkbrood. If you keep your colonies populous, warm, and dry they can take care of it.

  • I had a laying worker hive which I shook out. In going through the frames after dismantling the hive I noticed some brood which appears to be chalk brood. I didn’t have any of the conditions you cite other than a weak hive. I’m in the PNW too and as you know it’s been pretty hot. I have a slatted rack, SSB, and an upper entrance so I think ventilation was okay. I was also feeding them. I’m wondering if the chalkbrood was just caused by the fact that the brood was so scattered it couldn’t be properly cared for. anyway my main question is what to do about the frames. Although I was sorry to lose the hive, as a second year beekeeper i was kind of excited to finally have some extra drawn comb and honey stores to use as needed elsewhere. Are all these frames a loss? Also I wanted you to know that after doing quite a bit of research on laying worker hives and mulling over elaborate fixes your take on it helped me make the decision to shake them out. Maybe at some point I’ll have the resources and knowledge to try something different, but I think that was the right choice at this time. Thank you so much for your rational common sense approach, You’ve helped me more times than you know. Chris

    • Chris,

      This could be the wrong advice, so take it with a grain of salt. But I personally don’t consider chalkbrood a big deal. I tap the frames upside down and try to get most of the mummies out, but some always remain. I give these frames to an established colony and they’ve always cleaned them up. At one time, five or six years ago, I had a number of frames like that, perhaps 14 or 15. I just gave them to established colonies and haven’t seen chalkbrood since then.

      • Thanks so much for your reply. Ii was kind of leaning towards that. The way I uderstand it, it is one of those things that is out there all the time like other bacteria and fungi and if an organism is healthy it doesn’t seem to cause a problem.

  • Curious as to how you tell the difference between chilled brood and chalkbrood. I just found 3 small soft bees that are in pupae form with their proboscis out,, on the screened bottom board. It got down to 46 degrees quickly last night and i had just split a hive. No other choice on that. Not seeing anything in the brood that looks suspicious. Got bees April 29,so very new. Love all the information on your site,

    • Janet,

      Chilled brood looks like dead brood, soft as you describe it. Chalkbrood mummies are solid white and hard and look like pieces of chalk.

  • I had a hive diagnosed with chalkbrood. It has almost died out. I took the frames that had chalkbrood and scraped out the chalkbrood but notice that there was some wet brownish slime goo kind of stuff in there with them. Is that just part of the chalkbrood?

    • Debby,

      The way I understand it, the larva eats the spores and the disease begins to grow inside the bee gut where it steals nutrients form the developing bee. At some point the bee dies and the fungus and dead larva expand to fill the cell. Next comes the white fungal growth that you see. So there is a transitional period between the death of the bee and formation of the hard, white mummy. That transitional period is probably what you are seeing. In other words, the larva is dead and decaying (forming the brownish slime). When that part is also consumed by the fungus, it will become hard and white like the rest.

  • Hi my friend and I share an apiary we have between us 15 boxes some of these are nucs. the other day my friend bought two nucs from a friend of his and when we were transfering then a week later into a brood box we discovered that one nuc was infested with chalkbrood. would a shook swarm method sort this out and ehat should we doo with the old frames. When I melt my old wax I use a steamer and I find that this also cleans and sterelises the frames could we doo this with the frames that had chalkbrood? excuse my spelling not very good at it!!!.

  • Hi Rusty,

    We’re having a horrible, bumpy ride into spring. I’m experiencing my first taste of chalkbrood and doing everything I can to fatten the girls up for summer.

    I’m experimenting with treatment free as of this season. Part of my regime includes feeding Hive Alive supplement which I feel okay with for the time. I’m done the recommended 4 feedings but with the conditions was thinking of feeding more, what do you think?

    Are you a fan and believer of such products?

    Kind Regard,


    • Nichol,

      I have tried various ones over the years, but I find the best thing for honey bees is warm weather and a great nectar flow. Without good conditions, it’s hard to make the bees thrive. Good nutrition comes from having multiple sources of high-quality pollen over the course of a whole season.

  • Hello,
    I recently found one of my hives to be queenless. It has a fair amount of calm bees, but I found a large amount of larvae and debris lying on the screened bottom board. No supercedure or swarm cells are present. The larvae appear to have been cleared out of their cells. I did not find any chalk like mummies, the larvae were soft. I did not see any mites on the larvae. Is it ok to combine this small hive with another, or should I shake it out? Thank you!

    • Melanie,

      I can’t remember the exact number, but a certain number of larvae are culled for things like birth defects. I think it runs around 10%. It is fine to combine this colony with another.

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