The common fruit fly (Drosophila melanogaster), is running amock at the winery right now. With a rather large amount of Cabernet sauvignon fermentations all going at once, these annoying little diptera have come out of the woodwork, en masse. This is the same fly, with it's rather short, annoying little life-cycle that is used as a model organism in biology; including the study of genetics because it is easy to take care of, reproduces quickly, and lays tons of eggs. They are apparently very useful: Sister-in-law OTW assures me that they came in very handy when she was reading for her B.Sc at the University of Liverpool. That just may well be the case but I just can't handle them getting biblical on the rim of my glass when I am barrel sampling wine with some visiting dignitary.
Other than using DDT to rid yourself of these bothersome little devils, a relatively easy solution is to leave 'fruit fly traps' lying around, not foolproof but they help. Take a plastic drinking cup filled halfway with preferably still fermenting wine, cover the top with cling wrap, make an opening just big enough for them to crawl in and feed, but not large enough for them to get back out, and bingo! Darwin must have been on to something.