I tried them last summer, didnt notice much of a difference other thank the smell was nice. I agree with taking care of any moisture problem, keeping up with litter changes, using fly sticks/paper( one byc'er said her chickens like to eat the flies off the stick), I also hung cow fly ear tags in my "chicken stalls" where a couple of trios are in closer quarters. I have also wondered about the "fly predators" u can buy in the mail..... they are some sort of insect that kills flies but are harmless to livestock. Also, in the area of my big barn that NO animals are allowed, i sprinkle the blue crystals (gold marin fly bait) on the ground, it is expensive, but works very very well. I live in central louisiana, so im almost positive we have the worst insect problem in the U.S.