Editor’s Note: The following article is excerpted from the recently published PCT Field Guide for the Management of Structure-Infesting Flies, 2nd Edition.

Pest management is a problem-solving profession. A customer has a problem with an infestation of some pest, and it is the pest professional’s job to solve it. Each situation is different, with many factors influencing an infestation — type of pest involved, number of pests present, construction and maintenance of the building, contributing conditions, and sanitation practices. The pest professional’s knowledge and experience will even play a role in how quickly or effectively a particular pest problem will be solved.

Experience is the best teacher in the pest management profession. One can learn all about a pest’s biology and habits, but until he or she deals with that pest in actual situations, the professional will not appreciate just how different pests act and live in the field. Skilled professionals learn from their mistakes — and their successes. As they progress in their career in pest management, their ability to solve pest infestations will increase with each experience.

Review of “case studies” is a good way to pass knowledge learned to other pest professionals. The following cases describe situations involving fly infestations in structures. One of these cases might be of help in finding a solution that your firm is encountering.

Here are five case studies — three about small flies and two about filth flies — that might be similar to a current situation you’re facing.

Fruit fly, Drosophila melanogaster
Photos courtesy of Stoy Hedges.

Small Flies Case #1: Fruit Flies

A hospital was reporting a problem with small flies. Inspection revealed the flies were fruit flies. The flies were found in the hallway leading to the outside by the loading dock. No fly breeding sites could be found inside. Outside, the dumpster was located about 100 feet from the back door. The ground under the dumpster was regularly cleaned and no debris was present in which flies could breed, yet adult flies could be seen flying about. This dumpster, however, was equipped with a stationary compactor attached. The flies were found breeding up under the compactor where garbage and debris had slipped through cracks and become trapped on small ledges underneath the compactors (see photo above). When the compactor was washed, water fell through the cracks and kept the organic debris moist — hundreds of adult and larval flies were found here.

Fruit flies frequently breed in moist debris in and under dumpsters, like at the hospital in the case study described here.
Photos courtesy of Stoy Hedges.

The employee entry door of the hospital was located in a recessed alcove near this area, which was equipped with several bright lights. These lights were attracting flies during the evening to the area of the doorway. The flies then entered the building as people entered and exited. The customer was advised to clean under the compactor and seal the cracks around it. Sealing the cracks prevented debris from falling under the compactor. The customer was also advised to change the exterior lights near the doorway to bulbs which would be less attractive to insects.

Lessons Learned: Fruit flies seen inside can even be from a breeding source outside. The dumpster is usually involved.


Small Flies Case #2: Phorid Flies

During a routine quality control inspection of a hospital, the inspector noticed 100 or more phorid flies in the ILT located in the serving area of the cafeteria. No other light traps in the cafeteria or kitchen contained more than a couple of phorid flies. This indicated that an active breeding source of phorid flies were present somewhere in the serving area. Shining a flashlight into the drain nearest the light trap that captured the most flies revealed numerous live adult phorid flies. Fly larvae were found in the biofilm present on the sides of the drain. No other drain in the kitchen was found to have flies. The hospital’s housekeeping staff was instructed on how to properly clean the drains to eliminate the flies. All of the drains in the kitchen were cleaned as a precaution and to prevent future infestations.

Phorid flies can be captured by ILTs and serve as a sign of an infestation.
Photos courtesy of Stoy Hedges.
Phorid fly, Megaselia scalaris,
Photos courtesy of Stoy Hedges.








Lessons Learned: ILTs are useful tools to alert you to an infestation of flies and other types of flying insects. The catch trays of these traps must be emptied frequently (or glueboards replaced) so that one will know whether an infestation is new.

Small Flies Case #3: Moth Flies

Moth fly, Clogmia sp.
Photos courtesy of Stoy Hedges.

A homeowner was experiencing a problem with small flies in one bathroom. The service professional could not find the source. An entomologist was asked to look at the situation and identified the flies as moth flies. No evidence could be found of the flies breeding in any drains, however, the entomologist noticed that the bathroom where the flies were seen was located next to the bathroom in the master bedroom. These two bathrooms shared the same wall for their plumbing pipes. A couple of holes were drilled into this wall and several moth flies emerged soon after they were drilled. The customer authorized a larger opening to be made into the wall which exposed a water leak and a prime, active breeding source for moth flies. Correcting the leak, drying the area out, and repairing the wall solved the infestation. (Case study provided by Mike Corbitt)

Lessons Learned: Flies are not always breeding in areas accessible to your eyes. Wall voids can serve as breeding sites when leaks or other suitable conditions exist.

Filth Flies Case #1: House Flies & Blow Flies

House fly, Musca domestica
Photos courtesy of Stoy Hedges.

A brewery reported a fly problem during the summer months in one of the brewhouses. The brewhouse was equipped with several overhead doors, which were kept open to help cool off the interior on hot days. Unfortunately, the odors that emanated from the brewhouse attracted numerous flies. The brewery’s management team did not want the doors to be closed, which would have prevented the flies from entering. The problem was solved by advising the construction of large screens in wooden frames that fit in the frame of the overhead doors. These screens allowed ventilation in the form of outside air to enter while preventing flies from entering.

Lessons Learned: There is nothing better than proper exclusion to reduce or eliminate fly incursions into buildings.


Filth Flies Case #2: House Flies & Yellowjackets

Photos courtesy of Stoy Hedges.

Lessons Learned: Air movement can be used to great advantage when dealing with flies. This is why air doors can be useful in certain situations.

A fast food restaurant participates annually in a state fair. The building in which the restaurant operates is small, which forces the restaurant to keep exterior doors open to handle the large numbers of people entering and exiting while purchasing food. Because the doors could not be closed, flies and yellowjackets were provided easy entry into the restaurant. The restaurant manager was concerned because the flies and yellowjackets were attracted to the soft drink dispensers. The workers were especially concerned about the yellowjackets. Although the flies and yellowjackets could not be prevented from entering the restaurant, the problem with the drink dispenser was solved in a surprisingly easy fashion. Fans were installed so they would blow directly across the drink dispensers. The blowing air prevented flies and yellowjackets from reaching the soda dispensers. This stopgap measure satisfied the restaurant’s management team.