Phorid larvae (Megaselia halterata) are obligate mycelial feeders therefore, the adult flies are not attracted to oviposit in the compost until after spawning. The up to 6 mm long larvae feed on the growing mushroom mycelium but rarely on the fruiting body itself. They can be distinguished from sciarid larvae by the absence of the black head, and they develop more rapidly into a pupa.

The adult fly can be distinguished from the sciarid fly by the short antennae and by its rapid, jerky, running movement. Adult phorids act as a vector for dry bubble. 75 flies per m2 may already cause an outbreak of the disease. Phorid flies are unable to fly when the temperature falls below 12°C (54°F). In the past they have rarely infected mushroom houses after late fall. As there are now more and more warm days into November, this period is prolonged.

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