Step 2: Technique
+ Tin/Steel Cans
+ Screen (Aluminum Wire is my favorite, fiberglass works too.)
+ Glass or Plastic jars
+ Hair Ties
+ Needle and Thread
+ 2 Liter Bottles
+ Reusable/Disposable food containers
+ Spray paint
+ Copper wire (Coat hangers rust unless you paint them.)
My problem originated with attempts on my part to cook a meal out in my yard. As soon as the fire was lit, flies would gather in conspiracy. You could almost see the branches and leaves moving with the masses of them rubbing their little fore feet in anticipation of the hamburger, pickles, and mayonnaise being set out so they could descend in clouds. Then for dessert go across the road to the horse stable.
I could set out the raw hamburger, turn around and lose it in a mass of gray, green, and blue bodies. Needless to say my sex life suffered. I surfed the web for weeks trying to understand my problem, coming across pages of instructions making fools of flies by using 2liter bottles, sticky traps, stinky baits, and learned a new word, "pong!"
Several stinky years of experimentation later, I found a site that gave me a clue as how to design this trap. The model I built, made from 2 liter bottles, caught dozens of flies in the first 15 minutes I set it out. Cheap and easy to build, the open end of the bottle doesn't confuse the flies as much and the light coming from underneath allowed the flies to make up their own minds where to go.
For my second model, I took screen from a cloth screen and stiched it into a funnel with a relatively small hole in the tip of the cone. About 6mm (1/4 Inch), it's big enough to let the fly in and small enough to keep him confused so he can't get out. You will have to decide between longer thinner and short squat funnels, the flies can find themselves out if too short, and can't find their way in if too long.
My last model was to take Aluminum wire screen and fashion the entire cage - funnel assembly out of it. I then placed a riser to hold the assembly off the bottom of a 5 gallon black bucket. My hypothesis being the buzzing sound the flies make as another attractant.