Vinegar Fly
Common Fruit Fly
Drosophila melanogaster
Associated with a compost heap in Glendale, Maricopa Co., Arizona, USA. March 2013. This is a male; he will patrol about on over ripe fruits awaiting egg laying females to mate with.
Drosophilidae -- Pomace Fly Family
More is known about the biology of these flies than is known about human biology. Some might wonder why so much money and effort has been expended to study a bug instead of humans. It is because the bulk of human and fruit fly biology is shared, i.e. the same, and because scientists can conduct many sorts of experiments and research on insects that would be unethical with humans. We owe much to this humble organism for what it has taught us.
There are Drosophila species associated with rotting cacti, but the species most often encountered in the Sonoran Desert are those that frequent human habitations. There they use fallen citrus or waste fruit placed in our garbage bins. Along with the eggs, adult female flies also bring yeasts which proliferate and hasten the spoilage process. Yeasts become the flies' principal food.