June 19th, 2010


50 More Urban Species #18-19: Fruit fly, Dark-eyed fruit fly

Fruit fly Drosophila melanogaster

Dark-eyed fruit fly Drosophila repleta

There are several species of very small flies that one is likely to find in a kitchen. Besides the little house fly and the drain fly, there are a few types of fruit fly, including these two. Identifying small flies is important if you are interested in reducing their numbers, since different substances attract different flies.

D. melanogaster is attracted to the products of fermentation. A ripe fruit is just the thing to make these tiny reddish flies magically appear; a banana peel in the trash will work too. The fruit flies are there to lay eggs in the rotting fruit—their larvae will feed on the sugars and yeasts found there. Vinegar and wine come ready-made with these ingredients and open containers of these will also attract fruit flies.

D. repleta is a slightly larger fly, darker all around, with eyes that are noticeably darker than D. melanogaster’s. The dark-eyed fruit fly is not as interested in fruit—it is attracted to the bacterial scum that forms in places where food and water collect. A crack in a kitchen floor is an ideal nursery for dark-eyed fruit fly maggots, as are many parts of a dirty sink. D. melanogaster infestations last as long as the fruit is around, D. repleta infestations are long term, requiring deep cleaning of surfaces and cavities that are never otherwise cleaned. Products containing microbes that consume the bacterial slime that harbor dark-eyed fruit fly maggots are a safe and reportedly effective way to eliminate them. D. repleta is part of a complex of closely related species which fly geneticists are still trying to untangle and understand.

D. melanogaster is among the most important of all urban animals. Their rapid and profuse reproduction (under ideal conditions they can go from egg to adult in about a week) and the ease with which they can be raised in captivity, have made them ideal lab animals for genetic studies. Much of what science knows the building blocks of life and how they work is directly due to the study of these humble vinegar flies. Only the house mouse can compare when it comes to animal species that have contributed to the body of knowledge we have about ourselves.