Ascosphaera callicarpa is a fungus common on the larval feces of the solitary bee Chelostoma florisomne, which nests in the Phragmites reeds of thatched roofs in Europe.

Infected larvae appear shrunken, pale buff, covered by a weft of hyphae, with or without the production of ascomata.

The ascomata are greenish (immature) to black (mature) spore cysts produced on aerial hyphae above the larval cuticle, measuring 40–119 μm in diameter.

Cultures grown on Sabouraud dextrose agar show rapid growth after 2–6 days; they are white with abundant production of spore cysts when both mating strains are present.

Ascosphaera agra is the only species of the genus that has been found growing on plant material (grass silage) outside of the bee habitat.