Pest Control
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If you keep finding tiny, furry flies resting on the tiles beside the bath or above the kitchen sink, you almost certainly have drain flies. They are also called filter flies, moth flies or sewer flies. They are a nuisance rather than a danger, and they can be cleared, but only by dealing with where they breed.
How to recognise drain flies
Drain flies are small, about 2 to 5mm, grey or brown, and covered in fine hairs that make them look fuzzy, like a tiny moth. At rest they hold their wings over the body like a roof. They are weak fliers that tend to hop and flutter short distances rather than fly across a room, and they spend most of their time resting on walls and ceilings near where they bred.
They are most often seen in bathrooms, kitchens and utility rooms, and around floor drains in commercial premises.
Where they breed
The larvae live in the gelatinous film that lines drains and pipes, feeding on the organic matter in it. Anywhere that stays wet and collects that kind of build-up can breed them:
- sink, bath and shower drains, especially the section just below the plughole
- overflows on sinks and baths, which are rarely cleaned
- floor drains and gullies, and drains that are seldom used
- a broken or leaking waste pipe under a floor or behind a bath panel
- septic tanks, and soggy compost or wet debris outdoors
In warm conditions the life cycle from egg to adult can take as little as a week or two, so numbers build quickly once a drain suits them.
Finding the source
A simple test tells you which drain is the problem. Before bed, lay a strip of clear tape sticky side down across the plughole, leaving small gaps for air. If flies are breeding there, some will be stuck to the tape in the morning. Repeat for each sink, bath, shower and floor drain, and for the overflows.
If every drain is clean and the flies keep coming, the source is likely to be somewhere you cannot see, such as a cracked pipe under the floor, a leaking bath waste or a void where water collects.
How to get rid of drain flies
- Scrub the drain. Remove the plug or grate and use a long, stiff drain brush to scour the inside of the pipe and the overflow. Breaking up the film is the single most important step.
- Flush and treat. After scrubbing, flush with plenty of hot water, then use an enzyme or biological drain cleaner over several days to break down what is left. Bleach poured down the drain on its own runs straight past the film and rarely works.
- Fix leaks and standing water. Repair dripping taps and leaking pipes, and empty mop buckets, drip trays and anything else holding stagnant water.
- Run unused drains. Pour water into the drains of spare bathrooms and floor gullies regularly so the traps do not dry out.
- Clear the adults. Vacuum or use sticky traps for the flies you can see. They will stop once the breeding site is gone.
Drain flies at work
In commercial kitchens, food businesses and washrooms, drain flies usually point to floor drains, gullies and equipment drains that are missing from the cleaning schedule. For a business, flies of any kind around food areas are an issue for hygiene inspections, so it is worth dealing with the source rather than the symptoms. Our commercial pest control page covers how we work with businesses.
When to call us
Call us if the flies keep coming after you have cleaned the drains, or if you cannot find where they are breeding. We trace the source, treat it and tell you if the cause is a plumbing fault that needs a plumber or drainage contractor. See our fly control page for how we work.