I've been having a problem with the flies in my chicken coop. I have a 16x10 chicken pen would probably be more like it. It's completed enclosed with chicken wire and a hardware clothe type wire at the bottom. It sits directly on the ground. The hardware type wire is about 3 feet underground as well. Not to long after I put my chicks in there I had a huge increase in flies. I tried all different kinds to get them under control but it seemed hopeless. I had a few people tell me about Diatomaceous Earth. I went and got some and sprinkled it over half of there pen and put a small layer of shavings on top of it. I made sure the dust settled then I let the chicks check it out. One of my chicks which I have NEVER seen dust bathe walked into it, let out a crazy sounding peep and just literally dove in! She seemed so happy to have it. She kept going to new spots and was having a ball. Is this normal behavior for a chick? None of the others were this excited. Do they really know there is something different there? After watching her is just made me curious. 
