ANNUAL FLY CONTROL ISSUE: Where Did These Flies Come From?

Two years ago a consumer asked me to investigate a chronic fly problem that had plagued her home throughout the summer. She complained of thousands of small flies in her basement and about the pest control company she had hired for $250 to treat for the flies. After the company’s aerosol treatment had no lasting effect, they kept her money and indicated to her that there was nothing more they could do.

The flies were identified as small dung or sphaerocerid flies. An inspection was conducted to determine where these flies were coming from and it appeared that they were crawling out through the expansion joint and flying to the windows and lights in the basement. There was no sewer gas odor in the basement and no evidence indicating the flies were breeding in a broken drain or stack pipe. The evidence pointed toward a broken drain line under the basement concrete slab floor.

ONLINE ONLY: B&G Equipment Co.’s House Fly Program Report

ONLINE ONLY: B&G Equipment Co.’s House Fly Program Report B&G Equipment Company has made available to the public results from the B&G Integrated House Fly program, an all-inclusive program for commercial facilities. This comprehensive program for fly control can be downloaded in an easy-to-read PDF document at http://www.bgequip.com/Flytraining.pdf

It was recommended that a plumbing company be contracted to run a camera down the sewer lines to determine if there was a break (Note: My experience is that these cameras can only be inserted in major drain clean outs and can not be used in drains coming from tubs, showers, sinks and disposals.) Unfortunately the camera failed to detect a break in the main sewer line. The customer had only one option left — to break open the slab in several locations to determine if there was an undetected break in the sewer line.

The slab was opened and a massive accumulation of decaying organic matter was discovered. The source was a break in the connection between the kitchen sink line (with garbage disposal) and the main sewer line. The customer reported that the sludge was crawling with millions of small maggots. The customer removed as much of the organic matter as possible, had the connection repaired and applied lime to the contaminated area. The home has been fly free ever since.

LET’S MEET BOB. Bob complained of seeing up to 50 drain flies per day, typically in his basement. He reported that at one point he noticed a few flies outside under a deck area where he had previously stored old tree branches and other vegetative debris. The debris was removed several months prior to the fly outbreak. I investigated the problem, checking drains, air conditioning condensate lines, condensation around windows, dry sink traps and roof leaks, finding nothing that appeared to be a potential breeding site. Since most of the flies consistently were found in the basement, the evidence pointed toward a sewer line break under the basement floor.

The house was about 50 years old and constructed during the time when cast iron sewer pipes were used. The basement on the front of the house was completely below grade and on the back side it was a walkout. There was a steep grade on the lot but no indication that there was moisture under the house. During the previous year dead vegetation was stored outside the right front corner of the house and it was suspected that this could be the source of the infestation. However, this was removed and the situation failed to improve.
At this point, there was little doubt the breeding site was under the basement floor. At the pleading of the customer I acquiesced to do what I knew would not work, treating with foam insecticide under the slab. Not to my surprise the treatment failed and the infestation continued.

(The worst disaster I have known to occur from removing the breeding site of this type of fly infestation involved drain flies under a basement floor.)

Finally the customer agreed to contact a plumber who when he began to break open the slab, one half the basement floor collapsed. As it turned out the basement floor was poured over concrete pilings and during the 50 years after construction the soil under the slab settled 6 to 18 inches. The broken pipe was located, repaired and the fly problem eliminated, unfortunately at a cost of more than $30,000 in repairs.

Breeding sites under slabs frequently occur in homes and buildings that are 40 to 50 years old and have cast iron pipe drains systems. The break in the line is typically found at the junction of connecting lines feeding into the main sewer line or where settlement has occurred, causing the main line to break. The flies that typically exploit this situation are small dung flies (sphaero-ceridae), drain/filter/moth flies (psycho-didae) and humpbacked/scuttle flies (phoridae).

YOU GET WHAT YOU PAY FOR. A seasonal (winter) problem that I have encountered several times is fungus gnats in bank vaults constructed below grade. The moisture causing the problem has been seepage through the basement walls that are located behind the steel vault walls and are inaccessible for waterproofing. In this situation, eliminating the breeding site is not an option.

The property managers were aware of the situation, however, they requested that we spray to knockdown the adult flies and treat with a residual between the vault walls and the basement walls. The bank also used a dehumidifier to reduce the moisture in the vault area. These efforts reduced the problem but I do not expect them to eliminate it. It was also recommended that a light trap be used to reduce the adult population, but to date this recommendation has not been implemented.

DOWN ON THE FARM. Here is another case study our company has worked on. The following is a letter that was sent to the owner of a barn that had several fly control issues:

The following recommendations are based on the inspection conducted at your farm on May 19, 2000. At the time of the inspection house flies were the major problem. However, conditions noted during the inspection also are conducive to stable flies.

Several problems that contribute to fly breeding were noted during the inspection:
• Manure was being piled and accumulating outside the horse barn. Manure should be removed at least weekly or spread on the pastures using a manure spreader. If manure is spread and allowed to dry out it will not create a situation that supports fly development. Insecticide treatments of manure will not kill maggots and prevent breeding.
• Water collects in several locations in the barn. The water results from poor drainage around the exterior, lack of gutters and an underground spring. The grade around the exterior of the barn should be designed to keep water from accumulating near the base of the building. Gutters should be installed where appropriate and the down spouts routed to underground drainage pipes that carry water away from the barn. Flow of water from the spring head should be routed to the outside of the barn and into an underground drainage system.
• The level of the floor in the barn should be raised so that it is above the exterior grade. The floor throughout the barn and stalls should be leveled using stone and stone dust. This will help prevent water accumulation and facilitate the removal of manure.
• Large exhaust fans should be installed in the gables of the barn. This will reduce the heat load in the barn and the air circulation will help create an inhospitable situation for adult flies.

To control adult flies that enter the barn, the following recommendations are made in the sequence in which they should be implemented:

1. Spray exterior fly resting areas, which are typically cool shady areas on structures and plants, with a residual insecticide. Consider treating all buildings on the property. The product recommended for this treatment is a microencapsulated formulation containing lambda-cyhalothrin. The advantage of these products is that they will hold up in the rain and lasts 60 to 90 days without re-application.
2. Consider using non-chemical fly traps in pasture areas and in the barns to capture adult flies. The products recommended are: Musca-Terminator Fly trap (reusable), Musca-Doom (disposable) and/or the Catch ’N Pitch (disposable).
3. If the fly trap units fill up too quickly, e.g., two weeks or less, it may be necessary to use a bait or similar product. The products recommended are Musca-Cide Fly Bait with Fly Bait Station and QuikStrike. These products should be placed out of the reach of children, pets and livestock.
4. Install electrocuting light traps in the barn. To avoid attracting flying insects into the barn, these traps should be located away from exterior openings. They should be positioned at least 6 feet off the floor. A heavy population of flies in the barn can make this a high-maintenance item requiring regular service.

The author is technical director of American Pest Management, Takoma Park, Md. He can be reached at 301/891-2600 or rkramer@pctonline.com.

IDentification IS KEY

Flies are among the most difficult types of insects to identify. Even classifying a fly specimen to a particular insect family can be a daunting task, especially to someone not experienced in fly anatomy and taxonomy. However, fortunately, only a few species and families of flies routinely infest structures. Further, each has key identifying characters that enable one to feel reasonably certain of the identity of a fly found within a building. Flies belong to the order Diptera, which means "two wings." Flies are the only insects that possess only one pair of wings. All other insects with wings as adults have two pairs. The second set of wings in flies have evolved into balancing organs known as halteres. This organ resembles a bulb on a thick stalk and is located on the fly’ thorax under and behind the wings. The management of flies in and around structures can sometimes be difficult but almost always proves interesting. No two situations are exactly alike but each control effort will involve certain common steps. Sanitation, breeding source removal and exclusion are key steps in any fly management program. Before any management program can begin, the flies that are causing the problem must be correctly identified. Failure to correctly identify the fly or flies involved in a situation usually leads to the failure in controlling or eliminating the infestation. Editor’s note: This information was excerpted from PCT’s Pest Identification Series, Volume II: The Flies, which features cutting-edge CD-ROM technology, photography and 3-D imaging to educate pest management professionals in the finer points of fly identification and control. Order your copy of PCT’s Pest Identification Series, Volume II: The Flies for $59.95 per CD-ROM, $49.95 for two to five copies, $39.95 for six or more copies. Call 800/456-0707 or visit www.pctonline.com/store. Allow two to four weeks for delivery.