Muscina pascuorum

Muscina pascuorum can be distinguished from the common house fly (Musca domestica) and stable fly (Stomoxys calcitrans) by its behavior and seasonality—it appears on windowsills in autumn and winter rather than summer. It resembles M. stabulans and M. levida closely; precise identification requires examination of genitalia and thoracic chaetotaxy. Adults are medium-sized muscid flies with typical gray thoracic stripes.

Pasture lands and rural areas; woodland environments with abundant fungi. In autumn, adults seek shelter in buildings and are commonly found on windowsills. The species is associated with forested areas where larvae feed on fungi.

Native to Europe (Denmark, Norway, Sweden). Introduced and now widespread across North America: Canada (Ontario, Quebec, British Columbia), and United States from New Hampshire and New York west to Washington, Oregon, and California, and south to Florida, Texas, and New Mexico. First recorded in North America in 1916 at Ottawa, Ontario.

Adults are active in autumn and winter; commonly observed on windowsills during cooler months. Seasonal activity correlates with fungal fruiting in woodlands. Spring emergence from overwintering sites occurs as temperatures warm.

Larvae feed on fungi, particularly woodland mushrooms. Adults feed on nectar and other liquid food sources.

Larvae develop in fungi, not in carrion or manure. Pupation occurs in soil or decaying organic matter. Adults overwinter in buildings and other sheltered locations.

Adults enter buildings in autumn seeking overwintering shelter, accumulating on windowsills. They are attracted to light and warmth on sunny winter days. Unlike cluster flies (Pollenia rudis), they do not parasitize earthworms.

Decomposer; larvae contribute to fungal decomposition in forest ecosystems. Adults may serve as minor pollinators when feeding on nectar.

Considered a nuisance pest when adults enter homes in autumn and winter. Often mistaken for house flies or cluster flies. Can indicate abundant fungal growth in nearby woodlands. Not known to transmit disease or infest food products.

• Musca domesticaCommon house fly; differs in seasonality (summer peak), larval habitat (manure, decaying organic matter), and association with human structures year-round
• Stomoxys calcitransStable fly; differs in painful biting mouthparts, blood-feeding behavior, and summer activity period
• Muscina stabulansClosely allied species; requires examination of genitalia and chaetotaxy for reliable separation
• Muscina levidaClosely allied species; requires examination of genitalia and chaetotaxy for reliable separation
• Pollenia rudisCluster fly; differs in larger size, golden thoracic hairs, and parasitoid larvae that develop in earthworms

• Muscidae
• Diptera
• Europe
• North America
• introduced species
• fungivore
• overwintering pest
• windowsill fly
• autumn emergence
• pasture fly

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Encyrtid Holdings | Entomology Research Museum
• Managing External Parasites of Texas Cattle - AgriLife Extension Entomology
• Flies at the window - Muscina pascuorum — Bug of the Week
• Strathmore B-Lines: Surveying Grasslands and Pollinating Insects in the Strathmore Valley - Buglife Blog - Buglife
• National Meadows Day 2022 in Northern Ireland - Buglife Blog - Buglife
• The Distribution of Muscina Pascuorum Meigen in America
• THE DISTRIBUTION IN CANADA OF THE EUROPEAN SCAVENGER FLY, MUSCINA PASCUORUM MG