I think I might have read this on a thread here, but wanted to shout it from the barn top. We were having a horrible time with flies and nothing seemed to help much, including the stinky fly traps. I bought several packages of vanilla scented "christmas trees" like you put in your car. I hung one in each pen, one on the back porch and one on the front porch of the house....and we don't have anymore flies. I thought maybe it was a fluke so I didn't post right away...but it's been over 2 weeks now and still no flies. We do use DE and Stall Dry in the coops in addition to the vanilla air fresheners. I guess the flies hate the smell of it as much as I do. I'm not crazy about vanilla scented stuff but I'll sure tolerate it if it keeps the flies away.