The key identifying character for the moth fly is the unique pattern of veins in its wings. The entire body and wings of the moth fly are covered with tiny hairs, giving it a moth-like appearance. To the naked eye, this tiny pest might appear to be a small fly with fat wings; the aid of a magnifying glass reveals the unmistakable moth-like appearance. This small fly is no more than 1/8 inch in length including the wings. They are usually black in color.
Click on moth fly image to enlarge.
Moth fly adults can be quite annoying in homes, appearing from sinks and bathtub drains. These pests breed in tremendous numbers in sewer plants and are easily blown towards homes by the wind. Their small size enables them to penetrate ordinary fly screens. There have been noted cases of bronchial asthma caused by inhaling the dust resulting from the disintegration of such small flies.
Moth flies lay eggs in a mass of 30 to 100. These eggs hatch in less than 48 hours. The larvae and pupae of the moth fly live in the thin film found in drains, septic tank field lines or filter stones. The larvae feed on sediment, decaying vegetation and microscopic plants and animals. The larval stage lasts from 9 to 15 days and the pupal stage lasts from 20 to 40 hours. The newly emerged adult fly is sexually mature on emergence and copulates within the first few hours of its life.
The key to eliminating a moth fly infestation is finding the breeding sources and eliminating them.
Moth fly larvae live in the moist film that develops on the sides of a drain and in the drain's trap. The presence of many adult flies inside a drain is a good sign that the drain is a breeding site. To check for possible breeding sites, place a length of tape across drains (or cracks in the floor) without totally covering the opening. If the opening is totally covered, there will be no air flow and flies will not emerge. Check the tape periodically. If flies are found stuck to your tape, you have found a source. Eliminating this source is discussed in Moth Fly Elimination.
The number one source of moth fly infestations seems to be septic or sewer problems that have not been detected. The appearance of moth flies is often the first indication of another problem! There are many areas in a building where moth flies can breed, so do not end your inspection after you find one source. These pests love the organic debris found in sewers, septic tanks, drains, wet brooms and mops, even the soil close to a leaking or ruptured plumbing line. In homes, moth flies are generally found breeding in bathroom drains, particularly those in showers. Shower pans are prone to leaking and the area under the shower pan becomes an excellent breeding ground for moth flies.
Do not overlook the outdoors in your inspection. Any sign of moisture on an exterior wall or under a home should be investigated.
Although space sprays easily kill adult moth flies in a home and around patios and porches, they will not totally eliminate the fly infestation. Total control comes with locating and eliminating breeding sites discussed in Moth Fly Inspection. Use the Gold Stick pheromone trap to capture adult flies in kitchens, bathrooms or other areas where moth fly activity has been detected. If a drain is found to be a breeding ground, clean the drain thoroughly (scrubbing it , if possible) and use Drain Gel (formally called Fly Gel) to destroy the film harboring the organisms.
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