Fruit flies are a frequent guest these days when I am sitting outside in the late afternoon or evening with a glass of wine. If I leave the glass unattended for a few minutes, I often find it necessary to fish them out of the wine. I encounter them indoors too - buzzing around fresh peaches, nectarines, and bananas. Fruit flies are attracted to fruity, yeasty odors - the products of fruit ripening and fermentation. Away from human habitation, fruit flies are found on ripe and decaying fruit and vegetation, where they feed and lay eggs. The flies and their young feed on yeast, bacteria, and the fruit itself.
Decaying or fermenting fruit produces alcohol (ethanol), and it must be the odor of alcohol, at least in part, that attracts fruit flies to my glass. Fruit flies (particularly Drosophila melanogaster) are also a well-known model for genetic studies, and have been subjects of scientific work as diverse as experiments on aging and Parkinson's disease. You might also be surprised to learn that fruit flies are subjects for studies on the effects of alcohol consumption. Because they feed in fruit that may be in various stages of fermentation, fruit flies have some level of tolerance to alcohol, but they too exhibit symptoms of overindulgence. Fruit flies demonstrate similar stimulant and depressant effects to those observed in humans. Intoxicated adult male fruit flies attempt to court the next fruit fly they encounter - male or female. I guess we have more in common with fruit flies than we realize!
Common names of animals are often a source of confusion. The name fruit fly is also used for insects in an entirely different family from the Drosophila flies I'm discussing here. And, there are many species or kinds of Drosophila flies too. Drosophila flies may also be called vinegar flies or pomace flies, but most people call them fruit flies for their habit of flying around fruit in the kitchen. The particular fly I found on my wine glass, the spotted wing Drosophila, is a recent invader in Washington state, coming originally from Asia. It is a concern for local fruit growers because, unlike the common fruit fly, it can feed on fruit that is still ripening on the tree. The distribution of this fly around the world is another product of the Anthropocene. This tiny fly, which can't fly very far, has leapt from Asia to Hawaii in the 1980s, and from there to California and across the continental United States since 2008. Human commerce has deposited the fly in its new locations, where it has become an expensive problem, damaging fruit in orchards. The human transport of organisms in the Anthropocene results in changes to the ecosystem as native species are affected, and possibly costs to other human beings as in the case of the spotted wing Drosophila. So not only do we change the physical environment in the Anthropocene, but we are actively, though unintentionally, changing the biota directly too. The tiny fly on my glass in Seattle is a testimony to the larger forces at work in our environment unleashed by human activity. We can measure its effect on agriculture, but broader ecosystem effects are not yet understood. Will they displace native flies? Only time will tell. For now, be prepared to share a little of your favorite evening beverage with this newly arrived guest.