Stoy Hedges
Moth flies will be either gray or brown and resemble small moths due to their hairy bodies and wings.

Editor’s note: This article originally appeared in the summer 2020 edition of PCT Canada.

Long considered a nuisance pest, small flies may pose a public health threat. A study by Ecolab researchers published in the 2018 Journal of Food Protection found fruit flies can transfer bacteria like E. coli, salmonella and listeria in the laboratory, suggesting they play a role in the spread of foodborne pathogens.

For Andy Linares this makes perfect sense, considering the “muck and mire and filth and decay” that attract small flies. Linares is president of Bug Off Pest Control Center, a New York City-based distributor of pest control supplies that also provides training to the industry. In March 2020, he spoke to attendees of Pest Management Canada in Québec City about controlling fruit, phorid and moth flies.


The first step in controlling small flies is species identification. “If we know the species, we know where they like to breed and that narrows down the search,” explains Linares.

To identify the species, examine the fly’s wings using a loupe or magnifier. Then, look at the fly’s behavior or flight pattern, says Linares.

Fruit flies have a noticeable cross-vein in their wings. “It’s not enough to see red eyes because there are brown-eyed species,” Linares points out. These flies also hover. “They tend to have this helicopter effect as opposed to darting back and forth,” he says.

Fruit flies are attracted to early stages of decay and fermentation. This includes over-ripe and rotting fruit, spilled alcoholic beverages and syrup leaking from soda machine lines. Finding the breeding sites may be difficult since organic material can get pushed into cracks and crevices, like where grout is missing between tiles. “It does require a greater degree of focusing into those nice little tight spots; sometimes it is not as easy as a rotten onion in a sack,” says Linares of finding the breeding site.

Phorid flies do not have a cross vein in their wings. Instead, they have a prominent, darker costal view where the wing meets the thorax. In addition, this fly has a large, flattened femur on the hind leg. “When you disturb this fly, it will skip; it will skip and then take off,” says Linares.

Phorid flies are associated with advanced decay. The source of an infestation could be a dead animal, refuse or waste material. The flies are notorious for breeding in broken waste lines and in the polluted soil around a broken waste line. “Look for the muck and mire,” advises Linares. But don’t assume a broken waste line exists until you run a diagnostic test, he says.

Moth or drain flies have unique wings featuring a series of parallel veins. They also may have a fuzzy appearance because they’re often covered in scales. Scales can fall off, however, so this shouldn’t be your primary means of identification. “They are among the laziest fliers in the fly world,” says Linares. You’ll find them very close to the breeding site unless carried by air currents, and they’re slow to rouse.

“If you identify it, you’re dealing with polluted water and the film that polluted water creates on the surface,” says Linares. This might be found in a floor drain, gutter, urinal or sump pump. “The black larvae are very easy to identify because they are black,” he adds.

Stoy Hedges
Two of the more common small flies encounterd by pest control technicians are phorid flies (top) and fruit flies (bottom).


“You’ve got to seek out the breeding site and you know you’ve found it when you find the larvae,” says Linares. Use a flashlight and a spatula to scrape out decaying material in cracks and around equipment. Other useful tools include an endoscope and a retractable inspection mirror.

Likewise, it’s important to look for pupae, which crawl out of the breeding site and move to dry, protected areas. This way you can remove pupae before adults emerge, he says.

“The key to small fly control, and fly control in general, is not to focus on killing the adults,” Linares points out. “It’s a losing battle if all you’re focused on is trapping, zapping, swatting, spraying, baiting because this only affects the adult stage.” Adult small flies represent only about 5 percent of the entire fly population; control efforts aimed at the adults will deliver relief for about 10 days but then the fly population will rebound, he says.


“The main focus should be on sanitation; denying that female fly that breeding site where she can lay her eggs,” says Linares. This requires clients to take out the trash and wash waste receptacles. It also involves “micro-sanitation,” he explains. While a kitchen or workspace may look clean, cracks and crevices may harbor breeding sites. “You just can’t clean the surface at the edges, you’ve got to dig into those collection spots,” he says.

And pay attention if clients say they “hose down” the facility each night. Doing so can push debris into hard-to-reach areas. “A constant source of moisture is going to be very appealing to flies,” adds Linares. As such, encourage clients to remove debris thoroughly before hosing or mopping, and to use portable dryers to eliminate moisture. “The mantra should be ‘clean and dry,’” he says.

Give clients a short list of the most important actions to undertake to improve sanitation instead of overwhelming them with a comprehensive to-do list. Once they complete the top one or two items on the list, follow up with numbers three and four, and so on.

Bioremediation is a key element of sanitation. Products containing probiotic enzymes and beneficial bacteria can be applied to targeted hot spots like floors, mops and drains to digest the fat, oil and grease that cause sludge and muck. These products come in gels, liquids and foams, and aren’t considered pesticides from a regulatory standpoint. “It’s really a no brainer. You just apply it and walk away, but you have to be very diligent about (applying) it,” says Linares.


While you can’t rely exclusively on controlling adult flies “because you’ll always be playing catch up,” you can eliminate visible flies using traps, fly lights, air currents and chemical controls, says Linares.

He places “the least amount of importance” on chemical controls, which include aerosols, liquid residuals, insect growth regulators and baits. “If you have an over-reliance on chemicals, you will create a situation of resistance so eventually the chemicals that you use are going to be useless even on the adult members. Unless you focus on the other stuff, you will be contributing to the problem on a long-term basis,” says Linares.

He does not advise using electrocution devices near food-handling areas as they cause the insects to explode, blowing fly bits all over a kitchen.


From a business perspective, Linares suggests adding a surcharge for small fly work. “This is going to be more labor intensive and therefore should be more expensive,” he says. He also advocates setting aside one service visit in the rotation to tackle this work exclusively, instead of trying to accomplish it along with cockroach and rodent control tasks.