Step 8: What should be obvious
1) The bait doesn't have to be stinky. Forget having to find raw hamburger and letting it sit for several days. Leftovers are just fine. Think what flies like, beer, old spaghetti, bread.
2) I like to keep the slots in the bait tray about 1/4 inch. It keeps them from finding their way out of the bait tray back to the environment, and channel them toward the greater light to the cage. More slots allow the smell to circulate, flaps help to keep the light down.
3) The smell is the best attractant. If the smell doesn't get out then the flies won't come to it. While you can construct the trap with solid pieces of plastic cut from say a 2 liter bottle, it's better to just take apart an old screen.
4) You will need to cure the smells from the glue and paint. Flies avoid petroleum because they will get stuck and/or poisoned.
5) Having one big trap will work best in areas where you need to catch a lot of flies, like Cow Barns, Baseball Games, Horse Stables, and Church Socials. Having several small traps set around the yard will catch more flies in the general sense.
6) The longer the traps stay out, the more flies you take out of the local population. That translates into less flies able to breed. I just take the cage and put it in the freezer for an hour or two. The flies grow numb, stop moving, and then freeze to death.
7) If you have Fish, Turtles, or Chickens, you can make food out of them like this. If you want to save your flies, keep them in an airtight jar in the freezer. They get nasty and full of maggots (Yeah Really!) if you keep them next to the fishtank.
8) Save your Tuna Fish cans. Using them as bait holders in the bait chamber saves hours of cleanup time, especially after the flies have started a little family in the bait there. Throw out the old bait, rinse out the can, put in fresh bait! Breeding flies would be self-defeating...
9) Having other foods around like an uncovered trashcan will attract more flies. They will want to hover there rather than the smell of the trap.