Moth flies are fuzzy little flies with wing veins that run parallel from base to tip. In nature, they breed in moist, polluted environments that sometimes flood, where their larvae feed on decaying organic material. In and around structures, moth flies are common in plumbing drains and sewage systems. Because moth flies develop in decaying organic material, they may carry pathogens in healthcare facilities or to food handling areas. They may also cause allergic asthma in sensitive people.
Moth flies are one of the most common flies found in floor drains. Since the adults are poor fliers and are active at night, they are usually found resting during the day near the source of an infestation. They will breed in anything that collects moist organic material and are often found under leaking shower pans, in basement or crawlspace sump pits and in elevator pits. Structural or pipe leaks may also cause moth fly infestations.
The best way to manage moth flies is to remove or treat their breeding sites. The organic buildup on the inside of drain pipes can be scrubbed away and prevented by applying a microbial cleaner regularly. Or treat breeding sites with a boric acid dust to convert the organic buildup into a bait the larvae will eat. Another option is to apply a water-resistant dust that stays effective in wet and damp places.