Cluster fly (likely)

Adults commonly enter buildings for shelter, especially attics and wall voids, and occur outdoors in sunny areas near vegetation and soil. Larvae develop as parasites of earthworms.

Adults feed on flower nectar, honeydew, and other sugary liquids. Larvae consume earthworms internally.

Adults are sluggish, often bask on windows or cluster in warm sheltered spaces, and may overwinter indoors. They do not bite and reproduce outdoors, usually producing several generations annually.

They are generally harmless to people, livestock, food, and structures, though indoor aggregations can be a nuisance. Their larvae help regulate earthworm populations and adults contribute modestly to pollination and decomposition.