Fly control?

Question:Ive recently had a fly problem and I didnt want to use toxins so ive been using the sticky tape method. Then by suggestion from a friend I tried an old trick from portugal fill clear bags full of water and then tie them shut and hang them. This actually reduced considerably the amount of flies. What is the science behind this?

Answers:
The flies are contolled because the flies see their reflection in the water greatly magnified and see the reflection as a possible predator.