I felt like I was in Lord of the Flies this summer in my backyard. but t he Lord was an actual fly.  I was getting so many flies on our deck that it was hard to sit outside.  I bought this and it worked instantly.  It attracts the flies and kills them before you know it you have a pile up of flies in the container and not swarming around your face.  These are the refill packs so be sure to buy the plastic device for it as well- you won't want to see what is inside and it does a good job of hiding it.