Is It A Pest
for Drain Fly
Sometimes — and only as an indoor nuisance. A cluster pouring from a bathroom drain is worth acting on; an occasional fly is not. The fix is cleaning a drain, not treating a house. Source: https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ENTO-414/ENTO-414.pdf