Tracing the roots of a phorid fly invasion

Author’s Note: Rather than answering a reader’s question, this month I’m 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: Glen Ramsey, Ben Hottel and especially Frank Meek, BCE, who did the personal research.

The life cycle of a phorid fly. PHOTO: Courtesy GENE WHITE, [email protected]

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

The house is a crawl space construction with a municipal sewer pipe. According to Jim, two other houses east of his house are having phorid fly problems; the house in the west is not.

Jim went through the litany of what he’d done before turning to us:

  • His pest control service searched for sources several times and found none. He did not use a Rollins’ company for the recording.
  • His pest control service treated the drains several times with a foaming enzymatic cleaner with no effect.
  • He had his sewer and other pipes checked with a camera by a plumber, who confirmed there were no disruptions.
  • He contacted the city to run a smoke test on the sewer pipe leading to the house to make sure that the plumber’s inspection did not miss any leaks and to make sure no sewage gas was leaking into the house. No problems were found.
  • He consulted his local university extension service to confirm the identification of the insects.


To fix this phorid fly problem, we first checked Google Earth to see what was surrounding Jim’s property. In our estimation, this is a “normal” division. All of the houses looked fairly new – less than 20 years old and probably much younger. Jim says his house was built in late 2007 and completed in early 2008.

While there was agriculture in the area that could cause phorid fly problems, the prevailing winds did not come from that direction. There was a landfill that is now closed, but not very close, and the prevailing winds did not come from that direction.

We talked to Jim about whether there might be an old septic tank, or if the area was built on an old cemetery, etc. He said he was not aware of any such factors that could play a role. We teasingly asked if he suspected any neighbors of burying people in the back yard, and while laughing at our joke, he admitted that he suspected that a home’s sanitary practices were out of order and might be a possible source.

What we did next

The Rollins Technical Services team discussed the situation and decided that without a physical inspection we would not get any further. We had travel restrictions in June, but luckily Jim’s home was only an hour’s drive from our headquarters in Atlanta, Georgia. Frank volunteered to check it out.

Frank made it clear to Jim that this was a courtesy call and that we hadn’t expected to put him on an account. Rather, we offered to come up with a solution if we could and then let him figure out whether to do it himself or to hire a pest control company (any company). Frank’s inspection revealed the following:

  • Large numbers of dead phorid flies and live phorid flies have been found throughout the interior of the house.
  • No breeding grounds were found anywhere in the living room or crawl space.
  • Out in the northeast corner there were signs of phorid fly brood in rotting mulch overshadowed by overgrown shrubs.
  • Several external entry points were found that could be used by phorids to penetrate the structure.
  • Regarding the surrounding property, Jim announced that the problem started when a new owner moved in next door (northeast side). He says the neighbor doesn’t use a garbage service, collects garbage over a period of weeks / months and then removes it in a rental van, usually late at night.

Frank gave Jim five specific recommendations:

  • Seal gaps on the outside and around the foundation vents.
  • Treat entry points and resting surfaces with pesticides.
  • Remove and replace mulch and thin shrubs and other landscaping to reduce moisture build-up in the mulch.
  • Set traps in the mulch bed to act as an interceptor from the neighbor’s house.
  • Hire a pest control company to treat resting areas specifically for phorid flies.


Jim said that following Frank’s recommendations resulted in a dramatic decrease in live fly sightings, even though the population was still active throughout the summer. Then, on a hot August day, the neighbor opened her garage door several times within a few hours – literally causing 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 was taken out of service, but was refused entry to the neighbor’s house for inspection. He told the neighbor she had seven days to clean up the trash or impose fines. The neighbor denied having more than two garbage bags in the garage.

But the next morning, at 3:40 a.m., Jim watched the neighbor drag several garbage bags to a rented 15-foot van.

We followed up in early September and Jim reported that the issue was essentially fixed.


  • Always positively identify the pest. This will direct you where to look.
  • Always check everything, including areas that you don’t think could be a problem. Phorids that breed outdoors in mulch in a civil suburb are rare, but this was the case in this case.
  • As a pest control professional, never stick your nose into a fight with the neighbor. Let the homeowner take the lead. Have facts; Don’t make assumptions or blindly believe what the homeowner is telling you. It was pretty telling to check the levels of the interceptor flytrap even after the moisture problem in that area was resolved.
  • Trust your knowledge and your treatments. If the shared breeding grounds have been identified and treated, but the problem persists, think outside the box. Are you wondering where are you right now? Exploring every nook and cranny solved the case.
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