By Chris Williams on July 14, 2017.

I need some information about fourid flies? They’re driving us nuts! For about 6 weeks we’ve had tiny little black flies in the house that get in your face and land on you. They’re about the size of those fruit flies, but we actually had them identified by our extension office and they said they were fourid flies. O. L., Fitchburg, NH

I think you mean phorid flies and yes, they can be annoying and an ongoing problem. The bad news is that phorid flies breed in so many different materials and can be found in a variety of sites. To be able to advise you on how to get rid of them, we would first need to find out where they are coming from.

Phorid flies are only about 1/8-inch long with small heads and humped backs (you’d need a magnifier to see that). They’re sometimes called “humpbacked flies.” The tiny maggots of the larval stage feed in moist, decaying organic matter that is either plant or animal in origin. They can even become pests in mausoleums, morgues, or hospitals where they can feed on corpses or open wounds (see Phorid Flies Have Terrible Dining Habits!).


In a typical home there can be a number of sites that qualify and could breed phorid flies. These are just examples:

  • Decaying fruits or vegetables
  • Overwatered and soggy house plants
  • Rotting, cut flowers in a vase or arrangement
  • Dirty garbage cans, maybe with gunk accumulated under liner
  • Clogged drains or dirty garbage disposal
  • Scummy liquid in drip pans under refrigerators, hot water heaters, etc.
  • Dead mouse or other animal hidden in a void
  • Accumulations of dead insects in an attic or elsewhere
  • Animal feces, including human feces

This last one is a concern. When phorid flies are an ongoing problem in a building and there is no obvious source, we always have to suspect a septic or sewer line break. Usually, the flies are tracked to a line break which allows waste material to accumulate under the slab and provides a breeding ground for phorid flies. Emerging flies can follow light to a crack or expansion joint that lets them enter the structure above on a regular basis (see Phorid Flies – How to Find a Sewer Line Break).

As you can see, an inspection of your home is crucial. Simply spraying inside will kill flies as they emerge from their breeding site but it won’t stop new flies from emerging. The only way to do that is to find and eliminate the breeding source. Call Colonial Pest today and arrange an inspection.

Photo Credit : By Charles Schurch Lewallen –, CC BY 3.0, Link



We’re not satisfied until you are. Learn More