Wastewater-treatment
Guides
Psychoda alternata
trickling filter fly, drain fly, moth fly
Psychoda alternata is a small moth fly (family Psychodidae) native to North America that has become cosmopolitan through human transport. Adults are about 4 mm long with broad, hairy wings held rooflike over the body. The species is strongly associated with wastewater treatment systems, where larvae feed on microbial biofilms in trickling filters and percolating beds. It has also been documented as an emerging nuisance pest in potted plants at commercial nurseries. Adults are short-lived, non-feeding, and primarily active in subdued light.