How Fly Infestations Start in Your Commercial Building

Fly infestations in a commercial building can begin with just one employee leaving food in a locker or desk drawer. Flies are well-known for their stubbornness and rapid reproduction once they gain a foothold in a structure. 

Even businesses that don’t prep, sell or package foodstuffs can attract fly infestations. Your commercial building provides food, water and shelter, in addition to multiple points of entry. To prevent infestations from starting, you need to identify the type of fly and where they breed in non-food-handling environments. Here is a quick overview of the most common flies that infest commercial buildings, and where to look for them if you are not in the food-handling business.

House Flies

Flies are common in houses and retail or office environments. Fortunately, they are more of a sporadic nuisance rather than a pest that stays for the long-haul. House flies are usually spotted near their breeding sites or near open doors or windows. Negative air pressure has a tendency to draw them inside, so keeping windows and doors closed as often as possible is critical.

Fruit Flies

These pests are attracted to fruits and vegetables, trash and dirty dishes. Check the break room for any abandoned food or dishes, and keep these areas clean and tidy to eliminate them at the source. Fruit flies and their eggs like to hitch a ride with fruits and veggies that employees bring to work. Make sure your workers are disposing of all food waste properly and empty all garbage receptacles daily.

Drain Flies

Probably the most stubborn and hard to eliminate of all, drain flies breed and lay eggs in waste drain lines and infrequently flushed toilets. They have the potential to bring in pathogens from waste and sewage lines, so they are most easily found in bathrooms and kitchens with garbage disposals. Treating an infestation of drain flies is a high-priority pest control problem, and it requires some fairly complex pest control measures. 

Fungus Gnats

If you keep live plants in your building, check them regularly, especially if you see tiny flies buzzing around the office. These pests love damp soil, and their eggs tend to hatch when exposed to excessive moisture. Overwatering plants or similar damp conditions tend to drive infestations. So, monitor any live plants you or your tenants keep in the building for fungus gnat infestations. 

Phorid Flies

The least common of all infestations in non-food handling areas, phorid flies thrive on moisture and organic decay. More often than not, finding phorid flies in your commercial building indicates that there is a broken sewer line underneath a building or in its general vicinity. Treating the problem almost always requires the expertise of professionals, so it’s wise to contact both a pest control specialist and a plumbing general contractor.


Fly infestations are a symptom of a greater problem. When you see flies in your commercial building, the best policy is to contact a pest control professional to deal with the root cause. Businesses in Southeastern PA, Central PA, Baltimore, Washington D.C. and Delaware trust Presto Pest Control for all their fly infestation and pest control needs. Contact us today for more information.