Fly Problems Solved

A thorough investigation is the cornerstone of solving fly problems. Foremost in the process is identification of the species causing the problem. Experienced PCOs can usually readily identify common filth fly adults. However, smaller flies are difficult to identify even with magnification and experience and may require the assistance of an entomologist.

Fly larvae are more difficult to identify and this task usually requires magnification to see the anatomical features used in identification. It also requires knowledge of entomological terms not commonly used in our industry.

It is important to know that fly larvae are not all the same size and not all larvae should be referred to as "maggots." A maggot is tubular, tapering at one end and lacks a head capsule. The term generally applies to the larva of a filth fly. Other larvae, e.g., drain flies, fungus gnats and midges, have distinctive head capsules and some form of legs, e.g., prolegs or tubercles (bumps).

The size of the larva depends on the species involved in the infestation and the conditions existing during its development. Obviously, smaller flies, such as midges and drain flies, have smaller larvae whereas the larger filth flies have larvae 10 times larger than their smaller counterparts. Overcrowding and a lack of food typically causes larvae to be smaller, whereas an abundant food source and less crowded conditions produce a larger larva and fly. Thus, size is not a good identifying characteristic.

Case History 1: Ask The Right Questions. Two years ago I was asked to identify some fly larvae that had fallen out of a drop ceiling in a natural birthing room. This room had every convenience available for women who wanted to have a natural childbirth, down to a large rocking chair with quilt. The cost of this room was $5,000 per day. Thus, the hospital was anxious about leaving the room vacant for even a day, however, they were even more anxious about having fly larvae fall down on mothers and their newborns.

The larvae did not appear to be a common filth fly maggot so the technician collected several for identification. The head was well developed and there was an obvious breathing tube and both were dark-brown to black in color. In addition there were dark marks down the top side of the larvae. The larvae were identified as drain/moth/filter flies.

The site visit was unremarkable in that there was no obvious area, e.g., floor drains and sink drains, where the larvae were coming from. During the inspection, a few larvae were found at the foot of the bed that was positioned in the center of the room. It soon became apparent that the only place they could be coming from was the drop ceiling. However, the ceiling tile was not stained and there was no evidence of moisture.

Questioning the nursing staff revealed that the week before the larvae appeared there was a sewer line break above the room, the break was repaired, the sewage cleaned up and the ceiling tiles replaced. (Note: Always inquire about prior events that may have led to the problem.) Unfortunately, some larvae still remained and were finding their way around the tiles and dropping into the room. The few remaining larvae were removed and no further action was required since sanitation had resolved the problem.

Lessons learned: Eggs and pupae are virtually impossible for entomologists and the most experienced pest management professionals to identify. While pupae can not be readily identified, their size, shape and location may prove helpful in investigating fly problems.

Case History 2: Pupae and breeding sites. A recent problem involved hundreds of black blowflies in a row house. Immediately this should indicate that there is something dead nearby. However, there was no odor of a dead animal but there were hundreds of what appeared to be rat droppings on the floor next to the heating unit. On closer inspection it turned out that these "droppings" were fly pupae. The dryer and heater vents were inspected and nothing was found. However, outside curled up around the heater vent, was a dead raccoon infested with thousands of maggots.

Apparently the maggots were attracted to the warmth of the vent and were crawling through a crack and dropping into the area next to the heater. The raccoon was removed, the pupae vacuumed up and glue sticks were hung up to capture residual emerging flies. Because of fluctuating temperatures and our inability to remove all the maggots, the resolution of this problem took almost two weeks.

Lessons learned: It is important that PCOs be familiar with all life stages of the pests that they frequently encounter. Unfortunately, fly pupae are one of the insect life stages that many technicians fail to recognize.

The fly species must be identified so that biological factors, such as developmental time and reproductive potential, can be assessed. Furthermore, identification provides insight into the fly’s habits, such as breeding sites and reaction to light and cold — factors that are essential in developing a pest management plan.

Eliminating fly problems depends on several factors — most notable are the identification of the fly, locating the breeding site and obtaining the customer’s support in resolving the problem. Rarely, if ever, are fly problems solved by applying an insecticide either to kill the adults or the larvae.

Fly infestations can be exasperating — particularly when the source of the problem is not readily apparent. This is of particular concern when adult flies are the only evidence of infestation. Adult flies may remain near the breeding site and serve as a beacon in locating the breeding site. Here is a case history that illustrates this point:

Case History 3. Take care where you drink. Last year a technician was called out to an apartment to deal with a large drain fly problem. In this situation, only adult flies were found. The technician looked for contributing conditions that could cause hundreds of adult flies to suddenly appear. He checked for drain traps not holding water, dirty drains, dirty mops and buckets, sewer line breaks and for similar conditions which would facilitate development of these flies.

After he investigated all of these possibilities, he contacted me on his cell phone and in our conversation about a possible leak under the sink he mentioned that there was an inoperable garbage disposal. Upon further questioning the tenants indicated the disposal hadn’t worked since they moved in two months ago. Closer investigation of this disposal revealed accumulated decaying matter and the source of the flies. Cleaning and repair resolved the problem.

Several months ago a property manager for a building housing a prestigious law firm called and was upset because they were having a continuous problem with drain flies in a kitchen area. The flies were a continuous annoyance when they hosted luncheons in the adjacent conference room.

As requested, the technician brought in specimens that were confirmed as drain flies. By this time, the technician had made his investigation, checking for open drains, empty traps, open stack pipes, dirty mops and other potential breeding sites. He recommended cleaning the drains and cleaning up spilled syrup around the automatic soda fountain, which was accomplished. In fact, the soda dispenser was dismantled by the supplier and new components installed, but the problem persisted.

The one common denominator in this scenario was that the flies always seemed to be around the drink dispenser. Tenants consistently complained they were getting flies in their drinks, which drew our attention back to the drink dispenser, where we consistently found flies. During my inspection I shined my light down the drink dispenser drain and out crawled a drain fly. The plastic drain tube ran through the base cabinet and approximately ten feet through base cabinets to the sanitary drain. Several places along its length the tube dipped and coagulated decaying syrup containing drain fly larvae was found. The drain line was replaced and the problem was resolved.

Drain flies are not always in the drain. Last winter a landlord requested that I investigate a chronic drain fly problem in a basement apartment. I investigated the apartment for breeding sites, such as broken sewer lines, dirty drains, etc., but everything seemed normal.

During the inspection I noticed that several flies were around the front windows, however, many more were between the windows and their poorly maintained screen. It seemed odd that the flies would be trying to get outside since it was the middle of winter. In discussing the problem with the tenant, she indicated that the problem worsened on warm winter days.

At this point, I decided to inspect the outside of the building and found that the landlord had placed a thick layer of wet organic sludge on the flower beds in the front of the house that was ground level for the basement apartment windows. The tenant further indicated that the onset of the problem coincided with the placement of this organic material.

The problem was resolved by spreading the sludge out in a thin layer and allowing it to dry out.

Lessons learned. Undeniably the best solution for chronic fly infestations is to find the breeding site and eliminate it. Frequently this is easier said than done and it can be expensive.

Sidebar:

Another critical element in fly control is customer education and cooperation. Customers need to understand the breeding habits of flies — such as fungus gnats — and that management of these pests is dependent on habitat modification, which is their responsibility. However, there are situations in which the customer may not be able to realistically change the habitat.

Consideration should be given to the following techniques when trying to control flies:

• Exclusion, using screens, downdraft air curtains, door seals and other materials, can prevent entry of flies into the structure.

• Treat exterior resting sites, e.g., southern and western building exposures and areas marked with pepper-like fly specks, using a microencapsulated, suspension or wettable powder formulation.

• On the exterior, baits can be used for filth flies in areas that are inaccessible to children, domestic animals and wildlife.

• Locate exterior lighting away from structures and direct the light toward the building. Change lighting from mercury vapor to sodium vapor.

• Indoors, sticky traps, light traps and jar traps can be used to capture flies that gain entry. The location of these devices should be away from entry points. This reduces the risk of attracting flies into the structure.

Sidebar:

A seasonal (winter) problem that I have encountered several times are fungus gnats in bank vaults constructed below grade. The moisture causing the problem has been seepage through the basement walls which 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 manager is 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 is also using a dehumidifier to reduce the moisture in the vault area. These efforts have reduced the problem but have not eliminated it. It was also recommended that a light trap be used to reduce the adult population.

Lesson Learned: Successful fly pest management requires thorough investigation and knowledge, but more importantly it requires creative thinking to find the source of the problem and eliminate the infestation.

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 $250.00 to treat for the flies and after their aerosol treatment had no lasting effect kept her money and indicated 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.

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 drains, e.g., toilet, clean-out, 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 a 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. They have been fly free ever since.

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. The customer complained of seeing up to 50 drain flies per day. I personally investigated the problem, checking drains, air conditioning condensate lines, condensation around windows, roof leaks and despite everything the evidence pointed toward the basement.

The basement on the front of the house was completely below grade and on the backside it was a walkout. There was a very 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, foam treated under the slab with an insecticide. Not to my surprise the treatment failed and the infestation continued.

Finally the customer agreed to contact a plumber 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 fifty years after construction the soil under the slab settled 6-18 inches. The broken pipe was located, repaired and the fly problem eliminated, unfortunately at a cost of over $30,000.00 in repairs.

Lesson Learned: Breeding sites under slabs frequently occur in homes and buildings that are 40-50 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 which typically exploit this situation are small dung flies (sphaeroceridae), drain/filter/moth flies (psychodidae), and humpbacked/scuttle flies (phoridae).

The options for controlling fly infestations when the breeding site can not be located or is a remote location are very limited. In rural areas, house flies breeding at poultry, dairy and hog farms can migrate several miles and from virtually any direction to homes, schools and other structures where they become a significant nuisance. Remote breeding sites typically can not be addressed, therefore pest management efforts should focus on exclusion and adult fly control.