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Winter 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

February 14, 2012

Fruit flies: Love among the peelings

If you seek a little companionship, stay home and peel a ripe banana. You may soon get a visitor, or several: curious fruit flies, which seem to find their way into every home and office.

If the little flies are fortunate, the odors they're tracking will originate from the sloppy sweet rot of fermenting fruits — prime spots to propagate.

For a fly to crank up its life cycle, it must first find a fly of the opposite sex. The spark starts when an ardent male approaches a female and taps her with his foreleg. An organ on his leg can taste whether she's fertile and the right species. If so, the pursuit begins.

As a male chases the larger female, he extends a wing and vibrates it, playing his courtship song. He eventually gets close enough to lick her posterior and will attempt to mate.

But it's the female that makes the decisive move. If she finds the guy fly suitable, she'll spread her wings and allow him to mount, where he'll remain for as long as 20 minutes. Usually less.

The next day, a fertilized female can begin laying hundreds of eggs, preferring to deposit them onto that drooling peach you left out. Within a day or two, eggs hatch into tiny maggots that feast and molt for about four days before they wriggle off to find a dry spot to undergo metamorphosis. After four or five days, adults emerge, charged up and ready to mate in less than a day.

Scientists are keen on fruit flies as laboratory animals. The flies breed efficiently at room temperature, they have a rapid life cycle and they present visually distinctive sex differences and broad genetic variations. The insect is one of the most intensely studied organisms, the subject of more than a hundred years of genetic research.

Fruit flies may be welcome in the lab, but in the home they are pesky. People who let fruit decay in the wastebasket and then become annoyed by their swarm of new fly friends can end the fun with a vinegar trap, a small container of apple cider vinegar laced with a few drops of liquid soap. The soap breaks the vinegar's surface tension, allowing enticed flies to flounder and drown.

SOURCES: Cold Spring Harbor Protocols, National Academies Press, National Center for Biotechnology Information

Fruit flies mating, drosophila melanogaster