I just finished a month long battle with fruit flies. I tried several things including placing apple cider vinegar in a bowl. This definitely attracted the fruit flies but at the end of the day only two or three of the would drown. Most of the time they would just fly down, touch the vinegar, and fly out. Finally I came upon a solution that worked. I poured apple cider vinegar into a small plastic container, filling it to about a half inch from the top, placed a lid on it and poked a hole in the lid with a nail. The fruit flies would then crawl in through the nail hole and fly down to the vinegar, touch down, and fly back up. Except this time they hit the lid, panic and fly around frantically until they flew into the vinegar and eventually drown.