Drain flies: the tiny moths are not from the window - they are from the trap

Those tiny, fuzzy, moth-like insects hovering in ones and twos around the bathroom are drain flies (moth flies), and the window you keep opening is not the problem. They breed in the soft gel film that lines slow, slimy drains - and they will keep hatching there for weeks until the film goes. This is a cleaning problem wearing a pest costume.

Confirm it in one minute

Tape a clear plastic cup upside-down over the suspect drain overnight (tape one edge so air escapes). In the morning, adults stuck inside the cup confirm the breeding site - and if two drains are suspects, test both, because the answer is often not the one you watch them land on. They also breed in the overflow channel, under a loose toilet seat base, or in that forgotten mop bucket - anywhere wet, slow and gunky.

Break the cycle mechanically

Chemicals mostly bounce off the gel film; mechanics win. Clear the drain first - hair and sludge are the film's foundation (the slow shower drain method). Scrub the pipe walls: a drain brush, or a bent bottle brush, worked up and down the visible throat of the trap - you are physically removing the nursery. Flush with very hot water and finish with the trap: several kettles' worth over a few minutes, then the trap-clean routine (that page's smells and these flies share one root cause). Repeat the hot flush every couple of days for two weeks - eggs laid before the first scrub keep hatching, and the repeat is what outlasts their cycle.

The traps that help while you work

A shallow dish of water with a drop of washing-up liquid near the hover zone catches adults all day; the window-and-cup trick catches them at source. Neither matters unless the film dies - adults live about two weeks, which is exactly why a single deep clean feels like failure and a fortnightly rhythm feels like magic.

When it is not a cleaning problem

Flies returning immediately after a proper scrub, a sewer smell that will not leave (the post-trip smell), or gurgling with backflow points to a dried-out or broken trap, or a venting issue - the floor drain backflow page covers the drain side, and persistent cases earn the plumber (the DIY versus professional line applies to the drains too). And if the source turns out to be the septic or soakaway breathing back, that is a bigger conversation: the soakaway signs.

General information, not professional advice. Drain flies are nuisance pests, not hygiene emergencies - but a bathroom that grows its own wildlife deserves the fortnight of hot flushes.