How to Get Rid of Flies in Food Service

Editor's Note: This article originally appeared in the March/April print version of QA under the headline "Buzz Kill."

A fly walks into a food processing area. It’s not the start of a bad joke — it’s the start of a pest problem and a food safety issue. Flies are annoying. Also, they can carry many pathogens that can seriously impact food and human health. You don’t need to fly off the handle, though. Here’s how to manage these pesky pests to keep your facility safe and learn how to get rid of flies in food service.

FLYING UNDER THE RADAR.

Flies are relatively small insects that can easily sneak into a facility. They are a huge order of insects that encompass everything from tiny midges and mosquitoes to house flies and large horse flies. There are an estimated 17,000 species of flies just in the United States. Flies are different from all other types of insects because they only have one set of wings, while all other winged insects have two sets of wings.

In food processing and storage, flies can be an issue. Typically, we divide pest flies into two categories: large flies and small flies. Large flies apply to house flies, flesh flies, soldier flies and bottle flies. Small flies are fruit flies, moth flies, phorid flies and sometimes fungus gnats. These flies will have different food sources as larvae and adults, so they will be found in different habitats. Identification is important to figure out where they are coming from, what they are feeding on and how to manage them.

FLY ON THE WALL.

Seeing adult flies means there is a sanitation issue the insects are using as a food source. Large flies breed in areas that are at least damp and have wet organic material. This could be around dumpsters and trash areas, carrion, animal feces, sewers and more. Adults find suitable materials and lay their eggs on them. The larvae (also known as maggots) hatch and start feeding on that moist organic material. When they are ready to pupate, they crawl to drier areas, form a cocoon and emerge as new adults a short time later. While the adult flies consume some of the waste, the maggots are the stage eating the most. Large flies indicate a sanitation problem outside. Adult flies are getting inside through openings.

Small flies are usually the opposite problem: they are typically breeding inside. They will rest on walls fairly close to their food and breeding sites. Much like larger flies, these too require damp organic material to breed in. They will find this in drains and leaking pipes, around dishwashers and refrigerators, in overwatered potted plants and more.

DON’T WING IT.

Both small and large flies can transmit many pathogens. Some of those bacteria, viruses and parasites can be dangerous to humans and animals. House flies have been found to carry 100 human pathogens, according to a 2018 study published in the journal BMC Public Health. Research has shown they can spread foodborne pathogens such as E. coli, Listeria, Salmonella and more. Studies in healthcare facilities showed they not only carry drug-resistant bacteria — they can spread multi-drug-resistant bacteria.

Just like the larger flies, small flies have also been shown to spread foodborne pathogens. Fruit flies are vectors of foodborne pathogens. Moth flies in hospitals can spread Bacillus and Staphylococcus. Phorid flies were shown to carry Bacillus and Clostridium in a 2019 study published in the Journal of Medical Entomology.

Because they live on decomposing material, they easily pick up particles of food that may have these pathogens. Then, they fly to another area, drop those infected crumbs and contaminate other species. Ignoring fly problems can result not just in audit failures but can cause shutdowns and recalls.

FRUIT FLIES LIKE A BANANA.

As with any pest, sanitation is incredibly important when learning how to get rid of flies in food service. Without food, water and shelter, flies cannot survive. It is impossible to clean up every last bit of food, especially in food processing. Water sources will always be available inside and outside. Sanitation is easier said than done. Knowing sanitation will never be perfect means knowing what other tactics to use and where.

Even when it can’t be done perfectly, all efforts to decrease food sources or make them harder to access will help. Focus on the breeding sources where maggots are developing.

This effort starts outdoors for large flies. Trash should be removed regularly, and trash areas like dumpster pads should be on a regular cleaning schedule. Any dead animals should be eliminated as soon as they are discovered. Don’t forget any outdoor areas employees may use for snacking and eating. Standing water, clogged gutters, poorly draining roofs and anywhere else that stays damp should be reduced so organic material doesn’t build up. Prevent wildlife from getting near the structures by keeping vegetation low, grass mowed and any fruiting plants eliminated.

Small fly efforts should be directed inside. Drains should be cleaned with a foaming drain cleaner to fully remove the built-up material. Using bleach, ammonia and/or hot water will not be effective, as it will only get what’s on the surface, not deeper into where the maggots are. Any wet areas should be dried out and standing water removed. Multiple cleanings may be necessary to fully eliminate the material flies are feeding on. Small flies can also develop inside equipment like mixers, food transfer bins, ice machines and more.

CLIP THEIR WINGS.

While sanitation is the first line of defense, exclusion can keep many fly problems from, well, literally flying into a facility. Since large flies are most often breeding outdoors around dumpsters, recycling areas and other filthy areas, don’t let them in. Keeping doors shut and all openings sealed can greatly help. Don’t forget vents, HVAC systems and roof openings. Small flies are a bit more difficult to exclude since they come from indoor sources; however, there are drain covers and other sealing options that may work in a food facility. Sealing off rooms or sections of the facility can keep pests contained in one area instead of letting them fly free through the building.

BE A BUZZKILL.

Since perfect sanitation and complete exclusion aren’t realistic, other tools should be used to deal with fly issues. Insect light traps (ILTs) are commonly used in food facilities to intercept, capture and monitor flies. These are most effective for large flies. Large flies that enter a facility, typically through doors, are attracted to the bright lights and get stuck on the glue boards in the ILTs. While these do capture flies and prevent them from getting further into the structure, they will never catch every fly that slips in.

Small flies are weak fliers and don’t travel far from their breeding spots. Temporary or smaller ILTs can be temporarily placed in areas to gather information on what’s happening with populations. While less common, small flies may be coming from outside sources nearby, and ILTs can help with that.

ILTs are fantastic as a monitoring device. Identifying the species of fly and counting them can show an increase or decrease over time. When counts go up, it’s a good indication that something is happening. Maybe a door is being left open by employees. It could be a holiday week, and dumpsters weren’t emptied as usual. A decomposing animal may be in the vicinity, or a nearby drain may be the issue. ILTs provide information that something is amiss, but it still takes inspections to find the source.

YOUR FLY IS DOWN.

As with any good IPM program, pesticides have a role. An application of any product for either large or small flies will result in knocking down many of the adults. It won’t do anything for the developing larvae that are buried in their filthy habitats.

As already stated, conditions are rarely ideal, and not every sanitation issue can be remedied. Small fly habitats can be treated with a labeled product. While it won’t likely penetrate all the way through, as the maggots emerge to find a drier place to pupate, they will come in contact with it. Insect growth regulators (IGRs) are particularly helpful because they halt the growth process; maggots can’t reach the adult stage.

Large fly habitats can be treated the same way. Dumpster pads, trash bins and other areas with organic buildup (that can’t be removed) can be treated with a labeled insecticide and IGRs. It becomes complicated when that organic accumulation is from another property. Maybe the source just can’t be found. Targeted use of products on the adult resting spots can destroy those flies before they get inside. Treating around doors, vents and other openings can reduce those populations. Since adult flies fly mostly at eye level, focusing on the ground floor is often enough. It’s not a perfect situation and won’t eliminate the problem; however, it can reduce it to manageable levels.

YOU CATCH MORE FLIES…

Because it’s a food processing or storage site, all that good food being produced and the great smells are a big attraction to flies. It’s hard to find something enticing that will draw them away. There are fly baits that can be used as part of the IPM program. Scatter baits are used on the ground where there are flies gathering and/or maggots developing. Bait can also be used in small bait stations. These help get the bait off the ground and in the flight path of the adults. It also protects the bait from sun, rain and other weather events that can degrade it.

Bait also works like a monitor. Knowing how much bait was initially added and how much is left provides information on populations. If a full bait station is put out and all the bait is gone in a week, there’s more control that needs to happen around that area. With IPM tactics in place, there should be a decrease in feeding because there is a decrease in flies. Further management decisions can be made based on the collected data.

FIRST RULE OF FLIGHT CLUB.

Ignoring fly problems is a recipe for disaster. Sanitation issues can get progressively worse and even cause other pest problems. Small flies can develop from egg to adult in as little as seven days. Drains and other high-risk areas should be cleaned accordingly. Female house flies can lay over 500 eggs in three to four days. This quick development means an introduction of only a few flies can lead to an infestation crisis in a very short time. Ensure everyone at the site knows what to look for and who to tell when they see any flies or sanitation problems that could lead to fly issues. See something, say something is applicable to all pests.

Whoever is performing pest control duties (in-house or third party) should be counting flies on ILTs and recording that information so it can be analyzed. They should be inspecting for conducive conditions, especially sanitation issues. Maintenance teams need to fix structural issues such as door sweeps and screens. They need to know how to seal properly so pests can’t slip in. Everyone should know they play an important part in keeping the site free of pests. Communication between all departments involved is key.

DON’T FLY SOLO.

Both small and large fly problems can be complicated. When animals die in wall voids or crawl spaces, they can be hard to find and access. Small flies are adept at squeezing through tiny openings to enter homes. A professional, in-house or external, can help identify, find sources and provide the best options for sanitation, exclusion and treatment. Good communication will keep everyone up to date about who needs to do what.

There are great resources out there, so you don’t need to fly by the seat of your pants the next time you have to figure out how to get rid of flies in food service. Small or large, they are all a problem. Finding them quickly allows for faster and better treatment, keeping the site safe from these disease-carrying pests.