I've recently discovered a cheap, marvelous, safe way to catch flies.Put a little bit of water with a dash of dish soap mixed in with some balsamic or apple cider vinegar into a little plastic food container (like yogurt comes in!) with a hole cut in the middle of the lid. Wider is better than taller, I think, but have not scientifically proven--I'm suspecting the closer the liquid is to the hole, the better.The vinegar attracts the flies ( that old adage about honey and vinegar? not true! at least for fruit flies ), and the dish soap breaks the tension of the water so that they can't get out.