During the warm months of the year, each person likely has at least one encounter with a fly every day, even if it is as simple as noticing one flying by. In extreme cases, a homeowner or business experiences a serious fly invasion; one where the services of a pest professional may be needed. Flies belong to the order Diptera with more than 150,000 species described thus far worldwide. A relative tiny percent of these are known to be structural pests; however, mosquitoes and several other types of flies are society’s most important public health threat. Within structures, flies are considered a nuisance first and serve as a health concern when found in food production or health-care environments.
Some of our most frustrating days will involve flies, usually fruit or phorid flies, attempting to discover the locations or breeding sites and other conditions conducive to the infestation. Other fly issues are more easily answered. But the solutions always come back to the type of fly involved. This article will provide a few tips for key pest flies.
1. Start Outside. Most all house fly issues originate from the exterior. House flies (family Muscidae) breed primarily in animal manure and secondarily in moist, organic materials associated with Dumpsters and other trash receptacles. If found breeding indoors, the breeding site will most likely involve an overlooked trash can, poorly maintained trash room or rotting produce stored in boxes or bags. The only time I’ve encountered house flies breeding indoors involved an overlooked box half-full of rotting potatoes...in the middle of winter!
Where a house or building is located also may play a role in the numbers of house flies seen around/entering a building. Structures near farms where livestock are present are more prone to house flies, face flies, little house flies and even stable flies (family Muscidae) — all of which breed in fresh animal manure. The building doesn’t even need to be adjacent to the farm as house flies are capable of flying two to three miles, attracted by odors or other factors. When establishing a house fly management program, more comprehensive efforts often are needed for buildings afflicted by larger numbers of flies.
2. Focus on Trash Receptacles and Entryways. Is the customer keeping outside trash cans and Dumpsters clean? Are these located as far from doors as possible? Even clean Dumpsters and trash cans will attract some flies, but the messier receptacles bring more flies, thus increasing the number of flies potentially entering inside. Locating Dumpsters and trash cans as far from the building as possible helps minimize flies near entryways. Use of fly baits in these areas can be beneficial in reducing numbers of flies in the area.
Doors should not be propped open and when opened, should close within a few seconds. If ventilation is needed, such as seen with overhead doors in warehouses during summer, doors should be equipped with tight-fitting screens. Use of plastic curtains on overhead doors can help exclude flies where the doors are used frequently.
3. ILTs are 24-Hour Sentinels. A well-designed insect light trap program is essential for any commercial building with house fly issues. ILTs work attracting and catching flies 24 hours a day...as long as they are well maintained and UV bulbs are changed out as recommended by the manufacturer.
Placement of ILTs is key to effectiveness. If placed too near natural light, an ILT’s ability to attract flies during the daytime will be negated. Placement too high on a wall, above 5 feet, will decrease the numbers of house flies captured. Hanging an ILT too close to doorways allows flies to fly right past the trap before they even “see” it. Locating traps so they can be seen from the outside can attract nighttime flying insects to the building. Pest professionals have a variety of quality, economical ILT choices to offer customers. Design the ILT plan to follow the natural flow flies might take from entryways through the building. Use as many ILTs as needed — don’t settle for just one in the back and one in the front. Consult ILT manufacturers for advice for using their traps most effectively.
Blow Flies, Bottle Flies & Flesh Flies
1. Similar to House Flies. Relative to their presence in and around structures, blow and bottle flies (family Calliphoridae) and flesh flies (family Sarcophagidae) are similar to house flies. Such flies are attracted by garbage and food odors; most infestations originate from the exterior. Control strategies focused on sanitation, exclusion and ILTs are key for all these flies.
2. Where’s the Carcass? Blow flies and flesh flies both primarily breed in animal carcasses outdoors, often being the first insects to discover a freshly dead animal. When dozens of these flies suddenly appear inside, it’s a good bet that some animal has died within the walls, ceiling, attic, crawlspace or chimney. On two occasions of which I’m aware, the presence of blow flies led to the discovery of a dead man trapped in a chimney! Usually, though, a dead mouse, rat or bird is involved. I once found a dead mouse that had already been infested by blow fly larvae and when I allowed the flies to fully develop within a container, 125 blow flies were the result. Imagine the number of flies produced from a larger animal.
Although the cause is easy to discern in these cases, finding an animal carcass within the voids of a structure can be quite difficult. Blow fly and flesh fly larvae crawl out of the breeding material to find a place to pupate and often the larvae can be found dropping from ceilings or crawling along baseboards. If larvae are found on top of a counter, bed, etc., look for vents or light fixtures in the ceiling from which larvae could have emerged. Either investigate the attic directly above or inspect the ceiling void, remove the vent cover or fixture, and examine the void for an animal carcass.
3. Use Traps. ILTs and/or sticky traps can help remove adult flies quickly until the dead animal is discovered.
1. Freshly Decaying Materials. A number of different fruit fly species (family Drosophildae) may be found infesting homes, restaurants and other buildings. Fruit fly larvae feed on yeasts that develop in freshly decaying organic materials, usually those containing sugars. The first place to look is where fresh fruits and vegetables are stored outside of coolers. Experience has shown that a single onion, potato, lemon or banana can serve as a breeding site for fruit flies. From there, check trash cans, recycling bins and for pieces of fruit or vegetables kicked under tables or appliances. Don’t be surprised to find restaurant employees tossing half-eaten bananas or other fruit behind appliances, into false ceilings or onto the top of walk-in coolers.
I’ve found fruit flies breeding in drains, most often the drains in soft drink beverage towers. Also beware of leaks occurring with the lines that run from beverage towers to the boxes/canisters of syrups. Often, these lines run through walls, ceilings and under slab floors. A pinhole leak in one syrup line creates a breeding source for fruit (and phorid) flies that may not be easy to access. With floor drains, fruit flies may be found breeding in organics at the top of the drain but rarely are found deeper into the drain line. Last, in commercial kitchens, sugars and other organics can accumulate along and under baseboards, cracks at floor level and within the spaces of rubber floor mats.
2. Bacterial Cleaning Products. Obviously, the key to minimizing fruit fly infestations is through good sanitation practices. The varying levels of cleaning and maintenance in kitchens complicates the efforts for effective fruit fly management. Convincing the customer to convert their cleaning materials to the use of a bacteria-based cleaning product can be highly beneficial for fruit fly control.
The types and numbers of bacteria vary by product but all are designed to attack and consume sugars, greases and proteins present in the organic buildups in drains and on floors that support fruit, phorid and moth flies. Properly used, bacterial cleaning products deny fly larvae the foods they need to thrive and so, over time, fly populations plummet. Elimination of flies may not occur just with the use of such products alone if fruit flies are breeding in trash cans, recycle bins or other sites where bacterial products are not contacting.
For the bacteria to perform their job, the customer must refrain from using standard cleaning products, drain cleaners or bleach on floors and drains. Such chemicals will kill the bacteria. Additionally, customers should be advised that results may take a week or two. Consult the manufacturer of the bacterial cleaning product of choice for specific information on gaining the best results with each product.
3. Fruit Fly Traps. A number of effective fruit fly traps are available that will attract and remove adult flies while the search for and elimination of breeding sites is ongoing. When placed near suspected breeding sites, trapping adult fruit flies helps reduce the numbers seen by customers and employees. Traps also can be spaced uniformly in an area to help narrow the search for breeding site locations. The traps with the larger number of flies are likely closer to the breeding site.
1. Breeding Sites Highly Varied. Phorid, or humpbacked flies, (family Phoridae) are a large group of small flies known to exploit a large variety of breeding material. Although they can be found living in the same types of decaying organic matter as fruit flies, phorid flies can breed in materials in a high degree of decay, particularly in drains and drain lines, contaminated soil, rotting vegetation and dead animals. I once traced a phorid fly infestation back to an open pail of organic glue used in a bookbinding factory. In another case, the flies were found breeding in wet flour that had washed up into cracks beneath the equipment in a small bakery. When dealing with phorid flies, your inspections will need to be more far-ranging than those involving fruit flies.
2. Process of Elimination. Inspections should focus first on the more obvious sites for breeding such as drains, trash receptacles and wet debris trapped in cracks at floor level (use a putty knife or spatula). If phorid flies are not located or continue to be an issue after steps have been taken to clean up those breeding sites, you will have to look deeper. If walls are wet and could have flies breeding within, drill a small hole into the wall void(s) and tape a clear plastic cup containing an insect monitoring trap over the hole. Check it the next day. Adult flies, if inside the wall, will fly to the light coming through the hole and be snared on the trap. Any walls with flies will need to be opened by the maintenance staff to determine the issue and then corrected.
If a broken drain line is suspected beneath a slab floor, you can use the same clear cup/trap technique after drilling holes through the slab in areas where you suspect the drain line might be fractured or leaking. It may take a couple of days for flies to begin emerging from under the slab into the cups and if they do, then the customer needs to employ a plumber to scope the drain lines, find and fix the break.
With drain line breaks, it is extremely important that all wet, contaminated soil be removed and replaced with fresh soil at the time the drain line is repaired. If the contaminated soil remains, phorid flies will continue to breed and invade the building above. This fact also holds true for sub-slab drain line breaks involving moth flies.
3. The Odd Cases. With phorid flies, you can run into the once-in-a-lifetime kind of infestation. Be prepared to ask the customer about a building’s history and construction. A case involving a bathroom in a new Florida home was discovered when the pest professional opened the block foundation to access the bath trap under the soaker tub. Within the hollow blocks, he found a bag of feces a construction worker had tucked inside during construction.
A well known pest management consultant spent many days deducing the source of a major phorid fly problem in a hospital. Ultimately, he discovered the contractor had incorrectly installed the drain line system under the kitchen floor and for months food-laden water had been accumulating in the soil underneath. It took weeks of excavation of soil and installing the drain lines correctly to remedy the situation.
A large commercial building was discovered to have been constructed over a site where a soybean storage once stood. Apparently, a considerable amount of rotting soybeans had been covered with soil rather than removed, thus providing a continuous source of phorid flies filtering up into the building. Since the soybeans could not be removed, a “sump” area was dug under the slab where most of the fly activity filtering into the building appeared to originate. A light hung in the sump served to attract flies under the slab to the sump where a pipe and fan were used to direct them outside.
SUMMARY. Flies are adaptable creatures and nothing you discover should ever surprise you. Just remember that the flies we deal with all require moist, decaying organic materials of some kind to breed. Finding where these exist in and around a building and confirming which are being exploited by your target fly will often test your skills as a pest investigator. Be sure to question the customer and their maintenance staff about plumbing and maintenance issues and get them involved in cleaning up and making necessary repairs. Otherwise, flies will persist and your customers may be unhappy with your service.
The author is founder of Stoy Pest Consulting, Lakeland, Tenn.