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There are more than 130,000 species of flies worldwide, yet very few are structural pests. A few that are bothersome are not a whole lot bigger than a pinhead, said Stoy Hedges, owner of Stoy Pest Consulting, LLC.

When customers complain of small flies, the species Hedges looks for are fruit flies, phorid flies, moth flies and fungus gnats, all of which have different features and habits.

ID ADVICE. Hedges said there are two ways to help a PMP identify flies: (1) Observe their physical features and pay attention to where you’re finding them; and (2) understand which flies breed where.

“We need to be able to identify the fly particularly because they each have different habits,” he said. “You can have different breeding preferences and that can affect where you can look for them and sometimes how you control them.”

Fruit flies and phorid flies go from maggot to adult in as little as 7 to 14 days. Cleaning out trash and under equipment at ground level can eliminate breeding sites, he said. “You’ve got to know what you’re dealing with. Fruit flies breed in fresher materials. With moth flies, it’s more aqueous environments. And then you’ve got phorid flies, which kind of go both ways.”

Moth flies, also called drain flies, need standing water to breed. “Water that’s sitting on the floor under the dishwasher, where the grease and the flour and the other foods are rotting, will be associated with these flies,” Hedges said.

THINK LIKE A FLY. The larger the population of flies, the longer the breeding site has been around, which can lead to more breeding sites, said Hedges. Think about what motivates flies to be around and inside buildings. Some motivators are food, moisture, heat and light. “Larvae typically require some kind of moist area, particularly the ones we deal with indoors,” he said. “We also find them by window sills.”

The big factor in breeding, he said, is where food is and how trash is managed. “You’d be surprised how many fruit flies or phorid flies can breed in a single small lemon or grape or part of a piece of fruit at the bottom of a box or bag,” Hedges said.

With such tiny insects, Hedges said it’s incredibly easy to overlook something. He cited one time he found phorid flies breeding in a busted can of food and never would have found it if he didn’t find glue traps nearby that caught some of the flies.

Like the “can of food” situation, Hedges has encountered a lot of unpredictable breeding sites with phorid flies, some of which are mistaken for fruit flies. “I once traced a phorid fly infestation to an opened container of glue in a book-binding factory,” he said. Nevertheless, he said phorid flies are typically associated with drains, underneath slabs and cracks and spaces behind kitchen appliances.

ELIMINATE THE BREEDING SOURCE. Hedges said interviewing customers can save a lot of time. They know the facility and what changes have been made to it. Of course, he said, check your likely sources — areas associated with food or moisture. “But if you’re not finding them there, then you need to check sources in adjacent areas,” Hedges said. “You move out to the crawlspace, the ceiling above, the room above, the space below.”

Look for flaws in buildings that can lead to welcoming flies inside. Insects can get sucked inside when exterior doors (automatic ones too) are constantly opened and closed. Install screens, weather strips and keep doors closed.

A fruit fly infestation at a hospital was one of Hedges’ most frustrating jobs. He spent two days trying to find the breeding source where flies were near a heart catheterization unit. He started with drains and trash cans, but had no luck. He branched out and went on different floors, the kitchen, elevator shafts, outside and still...nothing. After the two-day search, Hedges was beside himself. He leaned against a window going over all the options in his head of where the breeding source could be located. He turned his head to the left where he saw a trash can shoved behind a support beam. The trash can was overflowing with thousands of fruit flies. “The maintenance people didn’t see it. You actually couldn’t see it unless you leaned your head against the wall and turned to the left, 20 feet from where the flies were being seen,” he said.

TRAPPED. Use traps to narrow down areas that capture the most flies. If Hedges wants to know if flies are breeding in a wall or floor, he drills a hole and puts a clear plastic cup and glue trap inside. “Flies, if they’re breeding in those sites under the floor, they will see the light emerging through the little hole,” he said. “They’ll enter the hole, get trapped and you can come back in a couple days and say ‘Hey, I got flies here.’” Customers can then properly hire for a job involving tile or flooring.

FlyWeb® traps and inexpensive light traps that go in outlets can help. “Place these throughout the facility and where I catch the most flies, that would be closest to where I would find the breeding source,” he said.