Most drain flies are harmless, but they can cause a problem if they encounter decomposing organic materials. They are generally active at night, searching for food and decomposing organic matter. They lay eggs in pipes and drains. They feed on biofilm that forms in pipe joints and recesses.
The best way to get rid of drain flies is to find their breeding site and remove it. To do this, you need to clean out the organic matter that they feed on in your drain. Drain cleaners will only temporarily control drain flies, because they do not kill their larvae. Fly paper strips and UV-light insect traps may be helpful in capturing some drain flies, but they will not eradicate them.
Drain flies are a nuisance that can appear in any household, but once you notice them, you’ll need to take action quickly. They can multiply very quickly, so you should start eliminating them as soon as they appear. They come from the sewer pipe and need a moist and dark environment to breed.
If you suspect your drain is breeding flies, check for puddles in your floor drain. If the water line is clogged, you’re more likely to find these flies. If it’s not, you can use a broom handle to tap it lightly. Then, make sure you clean the floor drain regularly.