Fruit flies are small, red-eyed, 1/4 inch long flies commonly associated with overripe and fermenting fruits and vegetables. However, fruit need not be present to have fruit flies, as they can originate from other sources.
Fruit flies can reproduce anywhere there is fermenting organic matter that stays consistently wet or moist. Like other flies, the fruit flies develop from larvae, and fruit fly larvae must have moist, fermenting organic matter in order to survive. The most likely of such sites in the home is a slow-moving or seldom-used sink, bathtub, shower, or floor drain in which a layer of slime (gelatinous film) has built up above the water line. Other moist accumulations of fermenting organic matter are possible and should be considered. These include wet areas under dripping pipes and refrigeration equipment, garbage containers, and discarded bottles and cans. Regardless of where the flies originate, they will be seen at windows and at sinks, as they are attracted to light and to moisture.
Fruit flies are best controlled by locating and eliminating the source of the infestation. Persistent presence of fruit fly adults indicates the larvae are developing nearby. Fly breeding areas are occasionally very difficult to locate and perseverance and imagination will be required. Refer to the list of possible breeding sites given above. One way to check individual drains is to cover the drain with a plastic film (e.g., "Saran Wrap"®) taped to the floor or fixture. If the flies are breeding in that drain, the adults will accumulate underneath the film within a day or two.
The most effective method to eliminate fruit flies developing in drains is to clean the inside of the drain pipe to eliminate the organic matter. Clean slow-moving drains with a stiff brush or other tool. Drains that cannot be scrubbed can be rinsed with water under high pressure or "sterilized" by slowly pouring boiling water down along the sides of the drain pipe. Another possibility is the use of a bacterial drain treatment that biodegrades the organic matter. Follow label directions carefully for best results. There is no benefit to treating drains with bleach or ammonia.
Household insecticide sprays labeled for fly control can be used to eliminate the adult flies that are present at the time of treatment but this will be only a temporary relief at best. Eradication will require eliminating the source of the infestation. For many people, fruit flies are a temporary annoyance and the flies eventually disappear on their own without a source ever being determined.
