Chalkbrood is often confused with chilled brood, caused when hives are opened when the weather is too cool, or by condensation forming inside the hive and dripping on the brood.
An infectious disease of bee larvae which is caused by a fungus Ascosphaera apis, it kills sealed brood, mummifying the larvae, with consequent weakening of bee colonies. It rarely kills a colony, but will weaken it, leading to a reduction in honey surplus and the possibility of the colony succumbing to other disease.
Larvae die after their cells have been capped, initially they appear fluffy and swollen but later shrink and become hard. Young infected larvae do not usually die or show signs of disease. Infected larvae usually die within two days of having been sealed in their cells. Some of the dead larvae remain chalky-white but others become dark blue-grey or almost black.
Hives can operate quite happily, despite the spores being present, if the colony is strong enough. There is no chemical control, often re-queening a colony will be effective treatment. Good hygienic behaviour by a colony, that is quick removal of the mummies by workers, appears to aid in clearing up the symptoms.