Yes, flies do sleep. About 60% of a fly's sleep occurs at night, and the remaining 40% consists of very short "naps" during the day.
In experiments, fruit flies have shown signs of sleep deprivation - flies that don't get enough sleep will later try to make up for it by sleeping longer or more often.
Scientists often study the sleep pattern of fruit flies as a means to learn more about sleep in animals and humans. Despite the numerous differences between fruit flies and other animals, there are striking similarities in sleep patterns and neurological behavior. Plus, compared to humans or animals, flies are much simpler and less expensive to study!
See The Journal of Experimental Biology for more info.
Posted 4192 day ago