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Published September 04, 2009, 05:06 PM

Solving fruit fly puzzle can be tricky

A cracked tomato, an overripe banana, an unrinsed beverage can in the recycling bin or a damp mop used to wipe up a punch spill: all are an open invitation to those pesky fruit flies!

By: Jim Stordahl, DL-Online


Fungus gnats and other small flies may invade the home, but the most common of the small flies is the fruit fly. Fruit flies are about 1/8 inch long, usually with red eyes and tan-colored bodies with striped abdomens. However, without close examination by a magnifying glass, they are just small flies.

Fruit fly infestations can occur at any time of the year, but are most common during later summer and fall because they are attracted to ripened or fermenting fruits and vegetables.

Fruit flies are attracted to fermenting or rotting smells. This could be caused by overripe fruit and vegetables, food residue in sinks, garbage disposals or trash containers and residue found in soft-drink, beer and wine containers. Their sudden appearance is always puzzling because, even if homeowners are very careful not to bring fruits or vegetable laden with flies into the home, they may show up in large numbers.

Although adult flies can enter the home through windows or doors, they are most often brought in the home as eggs or larvae in or on produce purchased in a supermarket or brought in from the garden. The life cycle of the fruit fly is about 8–10 days and it is estimated that a single female can lay up to 500 eggs, so their reproductive potential is great. The best way to control fruit flies is to locate and eliminate all potential breeding sites. This is not always an easy task because places where they are breeding may or may not be near where the fruit flies are most numerous.

Sometimes you need to think creatively and go beyond the ripe fruit and vegetables on the kitchen counter to find the breeding site. Keep in mind that a breeding site for fruit flies must include a fermenting organic food source, an area that is relatively undisturbed and a damp environment. This could be a leftover fruit or vegetable, like an onion or potato that has been pushed back into a corner and has begun to decay.

Other places to check include old food stuck to the bottom or sides of a trash container, dirty or clogged garbage disposals, the “gunk” that has collected in the drain of a sink, and collections of cans or bottles being saved for recycling.

Because they are attracted to fermenting smells, any pickling or vinegar mixtures or their containers should be checked including the tops of imperfectly sealed jars of pickled products. They have been found in mops or rags used to wipe up spills and even in grounds forgotten in a coffee or tea maker.

It may be tempting to spray the fruit flies with an insecticide, particularly if the breeding site is not easily located. An insecticide may reduce the number of adult flies, but is only a temporary solution because they reproduce so rapidly. As long as there is a food source, the fruit flies will continue to reappear. Patience and persistence in removing the food source is the only permanent solution to a fruit fly problem.


Source: Carl Hoffman, Stearns County Extension Service.