Soon after a fly dies from infection with this pathogenic fungus, large primary conidia are produced at the apex of a conidiophore which emerge from the intersegmental membranes.

The mycelium of the fungus may grow into an area of the brain that controls the behaviour of the fly, forcing it to land on a surface and crawl upwards.

[4] When it is critically ill, it tends to crawl to a high point, straighten its hind legs and open its wings, a behaviour that ensures that the fungal spores are dispersed as widely as possible.

[2] As well as the housefly Musca domestica, infection has been observed in adult flies in the families Calliphoridae, Culicidae, Drosophilidae, Muscidae, Sarcophagidae, Scathophagidae, Syrphidae and Tachinidae.

The fungus is found in most temperate regions and sporulation usually takes place in cool, humid conditions in areas where flies congregate and rest.