Fruit flies are fairly small creatures about the size of large aphids. They are true flies beloging to the order Diptera. Like all dipterans they have only 2 wings with a pair of knob like "stabilizers" replacing the missing wings.
Fruit flies are a serious pest. As with moths, it is the larva, the maggots, that cause the real damage.
A case in point is the infamous "medfly" (MEDiteranean fruit FLY) epidemic in California which
underscored the need for strict agricultural inspection and enforcement of border regulations.
Fruit flies are also often used in reasearch. Though they make a poor human model, they are very useful in genetic studies. The fact that they have only a few chromosomes, have a number of easily discernible genetic traits and are so easy and cheap to breed make them ideal for this kind of thing. Studies done on fruit flies laid the groundwork for later studies of the human genome.
In addition to the "whole body" pictures on this page, I have closeups of the fly's eyes , body hairs , legs , tail end and wings .