Drain Flies & Phorid Flies: The Tiny Bathroom/Kitchen Flies That Keep Coming Back
Drain flies vs phorid flies: how to tell them apart
Both are tiny and turn up in kitchens and bathrooms, but they behave differently. Drain flies (also called moth flies) are fuzzy, moth-like, and sit still on walls near sinks; they are weak fliers that flutter only short distances. Phorid flies are smaller, smooth, and scuttle across surfaces in a jerky, running motion before flying off — earning the nickname “scuttle flies.” Identifying which one you have matters, because phorid flies often signal a deeper problem such as a cracked drain or decaying matter under a floor.
Where they actually breed
• The gel-like biofilm coating the inside of drains, overflows and waste pipes.
• Slow or little-used traps where organic gunk accumulates — guest bathrooms, utility sinks, floor drains.
• Hidden leaks under floors or behind units, where damp, contaminated soil supports phorid larvae.
• Drip trays, dirty mop buckets, and the seals of waste bins.
Why they keep coming back after you spray
Spraying the adults you can see does nothing to the larvae breeding in the biofilm, so a fresh batch emerges within days. This is the single most common reason people feel they “can’t get rid” of them. Bleach is similarly disappointing: it may flush the surface but slides off the biofilm without removing it. Lasting control comes only from destroying the breeding film itself.
Step-by-step: clearing the source
• Identify the active drain — tape a clear plastic bag loosely over a suspect plughole overnight; flies caught inside confirm the source.
• Mechanically clean the pipe with a stiff drain brush to break up the biofilm.
• Apply an enzymatic drain treatment that digests the organic film (not just bleach).
• Run water weekly through little-used traps to stop them drying out and gunking up.
When to call a professional
If flies persist after cleaning the obvious drains, the breeding site is likely hidden — a cracked underground pipe, a leak beneath a floor, or a soil void — especially with phorid flies. A professional can pinpoint the source, apply targeted enzymatic programmes, and identify where plumbing repair is needed so the cycle stops for good.
FAQ
Are drain flies harmful? They don’t bite, but they can carry bacteria from drains onto surfaces, and large numbers are a hygiene concern in kitchens.
Why do I only see them in one room? They breed close to where they emerge, so concentration in one room usually points to a single drain or leak there.
Do you cover my area? Yes — we treat fly problems across Worcestershire, Herefordshire and Gloucestershire, usually within the same week.