Tracing the roots of a phorid fly invasion


November 20, 2020

Author’s Note: This month, instead of answering a reader’s question, I am sharing how we helped troubleshoot a homeowner’s very tough phorid fly account this summer. I enlisted the help of the entire Rollins technical team with this one: Glen Ramsey, Ben Hottel and especially Frank Meek, BCE, who investigated in person.



For purposes of this column, let’s call the homeowner Jim. He and his wife have lived in a house in Northwest Georgia for more than seven years, and began having a phorid fly issue about three years ago. Jim reports “thousands” of phorid flies are caught in warmer weather, but at least it calms down in winter. In summer, however, they have to use lids on their cups, for example, just to drink their morning coffee. Jim sent us multiple photos to prove this was a serious situation.

The home is crawlspace construction, with a city sewer line. According to Jim, two other houses to the east of his home have issues with phorid flies; the house to the west does not.

Jim went through the litany of what he had done before reaching out to us:

  • His pest control service inspected for sources multiple times and didn’t find any. For the record, he wasn’t using a Rollins firm.
  • His pest control service treated the drains multiple times with a foaming enzymatic cleaner, to no effect.
  • He had his sewer line and other pipes inspected by a plumber with a camera, who confirmed there were no breaks.
  • He contacted the city to conduct a smoke test on the sewer line running to the house, to ensure the plumber’s inspection did not miss any leaks, and to verify no sewer gas was venting into the home. No issues were found.
  • He consulted his local university extension service, to confirm the insect identification.


To troubleshoot this phorid fly issue, we first looked on Google Earth to see what was surrounding Jim’s property. By our estimation, this is a “normal” subdivision. All the homes looked fairly new — less than 20 years old and probably much younger. Jim says his house was built in late 2007 and finished in early 2008.

The area did have some agriculture nearby that could cause phorid fly issues, but the prevailing winds were not from that direction. There was a landfill that is now shut down, but it wasn’t very close, and the prevailing winds were not from that direction.

We followed up with Jim about whether there could be an old septic tank, or perhaps the area was built atop an old cemetery, etc. He said he was not aware of any such factors that could play a role. We teasingly asked whether he suspected any neighbors of burying people in the backyard, and while he laughed at our joke, he did admit he suspected one house’s sanitation practices were not up to par and could be a possible source.


The Rollins Technical Services team discussed the situation and decided we weren’t going to get any further without a physical inspection. We were under travel restrictions in June, but fortunately, Jim’s home was just a day’s drive from our Atlanta, Ga., headquarters. Frank volunteered to check it out.

Frank made it clear to Jim that this was a courtesy visit, and that we had no expectation of signing him to an account. Rather, we offered to develop a solution, if we could, and then let him figure out whether he wanted to do it himself or hire a pest control company (any company). Frank’s inspection netted the following:

  • Large numbers of dead phorid flies and live phorid fly activity were noted throughout the interior of the home.
  • No breeding sites were found anywhere in the living space or crawlspace.
  • Outside, in the northeast corner, there were signs of phorid fly breeding found in decaying mulch that was overshadowed by overgrown shrubs.
  • Several exterior entry points were found that could be exploited by phorids to enter the structure.
  • Regarding the surrounding property, Jim revealed the issue began when a new owner moved in next door (northeast side). He says the neighbor does not use trash service, accumulates trash over a period of weeks/months, then removes it all in a rental box truck, usually late at night.

Frank gave Jim five specific recommendations:

  • Seal gaps on exterior and around foundation vents.
  • Treat entry points and resting surfaces with pesticides.
  • Remove and replace mulch, and thin shrubs and other landscaping to lessen the accumulation of moisture in the mulch.
  • Place traps in the mulch bed to act as interceptors from the neighbor’s house.
  • Hire a pest management firm to specifically treat resting surfaces for phorid flies.


Jim said following Frank’s recommendations resulted in a dramatic decrease in live fly sightings, although the population was still active throughout the summer. Then one hot day in August, the neighbor opened her garage door several times over a period of a few hours— resulting in literally thousands of flies in and around Jim’s house.

Jim called the County Code Enforcement Office to file a complaint, and his other neighbors did the same.

A few days later, a Code Enforcement inspector drove out, but was denied entry into the neighbor’s home for inspection. He told the neighbor she had seven days to clean up the trash or face penalties. The neighbor denied having more than two bags of trash in the garage.

Yet the following morning, at 3:40 a.m., Jim observed the neighbor hauling several trash bags out to a 15-foot rented box truck.

We followed up in early September, and Jim reported the problem essentially was resolved.


  • Always positively identify the pest. This directs you where to look.
  • Always inspect everything, even areas you don’t think might be an issue. Phorids breeding outdoors in mulch in a middle-class, suburban neighborhood are rare, but that was the situation in this case.
  • As a pest management professional, never stick your nose in a battle with the neighbor. Let the homeowner take the lead. Have facts; don’t make assumptions or blindly believe what you are being told by the homeowner. Checking the interceptor fly trap levels, even after the moisture issue in that area was resolved, was pretty telling.
  • Trust your knowledge and treatments. If the common breeding sites have been identified and treated, but the issue remains, step outside the box. Ask yourself, where are they right now? Exploring all angles solved the case.

Leave A Comment

Comments are closed.