Chalkbrood is caused by the fungus Ascosphaera apis, which infects honeybee larvae after they swallow spores in their food. The fungus germinates inside the gut, pushes through the larval cuticle, and overgrows the whole larva with white mycelium. Once the larva dries out it becomes a hard, chalk-like "mummy" — white if only one mating strain is present, or grey-black where both strains meet and sporulate.
Each hexagonal cell on this comb carries its own larva through that life cycle: healthy → infected (mycelium spreading) → mummified, and — if the colony is hygienic — removed by workers who uncap and drag the mummy out before it can release more spores.
Chalkbrood mummies rattle audibly when a comb is shaken — beekeepers often diagnose it by ear before they even see the pale, chalky remains lying at the hive entrance or on the bottom board.
A hexagonal brood comb where each larva lives through the chalkbrood life cycle in miniature — healthy, infected by spreading mycelium, mummified into a chalky (or dark, sporulating) lump, and, if the colony is hygienic, uncapped and removed by workers.
Cooler brood temperature and higher humidity both push Ascosphaera apis spores toward germination, while cells outside the bee cluster's coverage chill fastest and turn to mycelium and mummies soonest — visibly linking hive conditions to disease spread.
Lower the brood nest temperature or raise humidity to watch infection accelerate, shrink cluster coverage to expose more of the comb to chilling, and raise hygienic stock selection to see worker bees patrol the comb and clear mummies before they build up.
About 15% of the cells here are modelled as drone cells, which sit at the cooler margins of a real brood nest — their mummies often sporulate into the tell-tale grey-black colour beekeepers use to confirm a chalkbrood diagnosis.