False Stable Fly

Muscina stabulans (family Muscidae) is a stout grey-black fly, 7-9 mm long, resembling a large house fly but distinguished by four dark thoracic stripes and an orange-yellow tip to the scutellum and palps. Females lay 140-200 eggs on decaying vegetable matter, manure, carrion, or garbage. Larvae are cream-colored maggots that begin as saprophages and become facultative predators in later instars, attacking other fly larvae in the same substrate. Development takes 15-25 days, longer than house fly, and the species overwinters as pupae or as adults in sheltered structures.

Adults are non-biting sponging feeders attracted to sweets, decaying produce, feces, and carrion, and readily alight on human food, making them mechanical vectors of enteric bacteria and helminth eggs. They are less strongly synanthropic than the house fly but frequently enter homes in cool weather and are often the large 'house fly' seen indoors in autumn and early spring. Larvae are agents of accidental intestinal and urogenital myiasis when eggs or larvae are ingested with contaminated food. The predatory later instars can suppress co-occurring house fly larvae in the same medium.