Hi, this is my take on things...everybody has an opinion.... At my ranch in north central Texas, fly traps have been working in the barns in conjunction with sticky strips. In one barn, I have 2 fly traps, one higher, one near the ground, and sticky strips next to them, maybe 10 inches away. Flies, attracted to the stench, land on the sticky strips sometimes (they get covered so they do land there) and sometimes go in the traps. Often, I see flies on the small paracord suspending the traps, so I got the idea to hang a trap from the bottom of a sticky strip in my chicken "barn" (96' x 40' old rabbit barn until I get them a proper coop...I'm growing here...). That works great!
These "put water in the plastic bag and hang them" traps are NOT for indoor use...they REAK! (reek?)...they STINK! But they do catch flies.
I've read that foraging flies are near the ground.... Maybe putting traps nearer the floor/ground would help. Three of my four current traps are near the ground and working well, but so is the one about 4 feet of the ground. Same for the sticky strips. We used to use Golden Malrin (sp?) fly killer in the '80's in the Rabbit Barn. Worked great. I tried some about 10 years ago, about 6 feet off the ground, and was not impressed...maybe it changed, maybe the height of offering matters?
Suggestions to keep the areas clean and free of food/stench sources are good but require a fair amount of labor. Suggestions to use a fly swatter and electric swatters mean, unless you can get the government to compensate you for "scalps", you're backing up, not moving forwards, if you know what I mean.
--HC