Ask The Entomologist question about drain flies

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Every now and then I notice several really tiny brown flies that most linger around the bathroom and kitchen. They’re so small that I can’t even see any wings and when I smash them, it leaves a red stain. I don’t think they bite, but they are extremely annoying. They sound like what I’ve read about drain flies but they don’t really look like the pictures I’ve found. What can these be and how do I get rid of them?

Drain flies are pretty visible and they are grey and fuzzy.  Most of the time you will see them resting or “hopping” along the walls.  What your are probably seeing are phorid flies.  Phorid flies are tiny and breed in decaying organic materials.  They usually don’t come from the drains unless you have a garbage disposal that needs to be cleaned out.  The larvae feed on rotting fruits and vegetables, bits of food that may have gotten swept under the fridge or cabinets, or overwatered plants.  Look in areas that stay moist where food items could have been spilled.  Sometimes they can come from dirty pet dishes, dirty trash cans, a water leak, or a dead animal in the crawlspace or attic.  Once you find the wet, rotting materials and clean it up the flies will go away.