I have
chickens, but I don't have a fly problem. I have
garden spiders. They are all over the place. Two years ago, I noticed a three or four in the garden. They spun egg sacs and left them in odd places, so I would carefully move them to where they might be a little more protected. Last year, when they started hatching, there were hundreds, all over the place. I had a kumquat tree that was covered with them, and they managed to disperse throughout the garden. Last winter, there were even more egg sacs than the winter before. Again I carefully moved some, spread them around. Now I have to watch where I step in the garden, as the spiders seem to be everywhere. Up in the eaves, inside the fig
trees, on the fences, under the deck, anchored to a
trellis, there are a whole mess of them around here. But little in the way of flies.
If your
chickens are free ranging, they will find these spiders a tasty snack, but
enough should be out of reach, that if you look out for them, they can and will take take of your flying insect problem.