Inspection
for Drain Fly
Confirm the species first, since fruit flies and phorid flies trace to different sources. Run the clear-tape test on each suspect drain and appliance condensate pan to pinpoint the breeding site; if indoor drains are clean, check outdoor wet spots and consider a broken sewer line behind a very large outbreak. Source: https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ENTO-414/ENTO-414.pdf Source: https://wpcdn.web.wsu.edu/wp-puyallup/uploads/sites/415/2014/12/PNW_PPDrainFlies.pdf