Fruit flies are the most common flying insects found in and around compost bins. These insects are not dangerous or harmful; however, their presence can be a nuisance, particularly indoors. A little information about the food and environments these insects are attracted to can be used to help us control their presence in places where they are not wanted.

There are many species of fruit flies, ranging in size from one to two millimeters. They can be recognized by the rather bulbous shape of their lower bodies, which is frequently an orange or light brown color. They are relatively slow flyers, often hovering around fruit or juice.

Indoor compost bins provide favorable conditions for the reproduction of these insects, but occasionally fruit flies seem to appear in our kitchens as if by spontaneous generation, even without the presence of a worm bin. This is because they can travel into our homes, unbeknownst to us, as larvae on the fruit we buy. The adults lay their eggs, invisible to the naked eye, on bananas and other fruits, which later hatch while the fruit is in our fruit bowls. If we put fruit skins containing fruit fly larvae into our compost bins, we soon have a healthy population of fruit flies in and around the worm bin. It is advisable not to add any more food to the compost bin until the fruit flies are gone. Since banana peels seem to be the most common bearer of fruit fly larvae, some people prefer to compost banana peels in outdoor bins only.

Fortunately, fruit flies have an excellent sense of smell and are strongly attracted by bananas. A simple, nontoxic, inexpensive, humane way to trap them is to place a banana peel inside a clear plastic container and make three or four holes in the cover with a standard round toothpick. Be sure to pull the toothpick all the way through the plastic and wiggle it around to make a hole large enough for a fruit fly to crawl through. Place the plastic container in or near the fruit bowl, not inside the compost bin. Within 24 hours, about 99 percent of the fruit flies will be inside the plastic container, having entered the holes and not found their way out.

Some species of fruit flies are larger than others. If you see fruit flies crawling around on the surface of your plastic container but not going inside, make the holes larger. (more…)