This works great for gnats. It catches dozens every day. But it only catches an occasional house fly, even when 50 are flying around the house. I've tried it in many different locations, made sure no other light is on any where in the house. It will catch 1 or 2 flies only. I added dry cat food to lure the flies, and now it catches 4 or 5 house flies. But I live in a farming area, and have 20 flies at a time flying in my house in the summer. For me, this just isn't good enough results.