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Quick answer: Drain flies, also called moth flies, are tiny fuzzy gray flies that breed in the gelatinous organic film lining drains, traps, and sewage areas. They are weak fliers seen resting on walls near sinks. Getting rid of drain flies requires physically cleaning the film out of the affected drain — chemical pours and sprays alone rarely work.
What do drain flies look like?
Drain flies (moth flies) are tiny, fuzzy, gray-to-tan flies with rounded wings held roof-like over the body, giving a moth-like look. They are weak fliers that hop and rest on walls, ceilings, and fixtures near sinks, tubs, and floor drains.
Signs of drain flies
You will see small fuzzy flies resting on surfaces near drains, especially in bathrooms, basements, and utility areas. They tend to appear in the same spots each day near the breeding drain.
Where drain flies breed
Larvae develop in the gelatinous organic film that lines drains, P-traps, overflow pipes, and condensate or sewage lines. Slow, clogged, or rarely used drains are prime breeding sites.
How to get rid of drain flies
First find the breeding drain with an overnight tape test. Then physically remove the film: scrub the drain and P-trap with a stiff brush, flush with hot water, and use an enzyme drain cleaner that digests the organic matter. Bleach and surface sprays usually fail because they do not remove the film where larvae live. Fix slow drains and leaks that keep the film wet.
When to call a professional
If drain flies persist after cleaning, the source may be a hidden or broken line, a sewage leak, or condensate pan. A professional can locate the true breeding site and correct the underlying sanitation or plumbing condition.
A Brooklyn-based, NYSDEC-registered company (Reg. #15140) led by Jorge Bedoya, an Associate Certified Entomologist (ACE). For pests in your home or building, NYE provides IPM-based, low-exposure control matched to the exact pest and verified with a follow-up. ACE-led work comes with a client portal of service reports and photos, fully bilingual service, and no long-term contract.
Drain Fly FAQ
How do I identify drain flies?
Drain flies are about 1/16 to 1/8 inch, gray to tan, and fuzzy, with rounded moth-like wings held roof-like over the body. They rest on walls near drains and fly weakly in short hops.
What causes drain flies?
They breed in the slimy organic film that coats the inside of drains, traps, and sewage or condensate lines. A slow or little-used drain is a common source.
How do you get rid of drain flies?
Identify the breeding drain (tape test), then physically scrub or brush out the organic film and flush it. Enzyme drain cleaners help; bleach pours and surface sprays usually do not reach the film.
How do I find which drain they are breeding in?
Cover suspect drains overnight with tape sticky-side down; the drain that traps emerging flies is the breeding site.
Are drain flies harmful?
They do not bite and are mainly a nuisance, though large numbers indicate a sanitation or plumbing issue that should be corrected.
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