I live here in North Central Arkansas, not far from Missouri line, I have 9 of my mules in a small pasture here by the house. They like to go in the same places, but not the same place I would like them to. I usually wind up taking the front end loader and scooping it all up and pushing it up in a pile. When the pile gets 8' high or so (usually 2 or 3 times a year) I load it up in an old 1 ton dump I have and move it to where I need it, usually 3 or 4 loads each time. The garden or the yard or somewhere. That is how I have made topsoil in most of my yard, as mostly all we have is rock. They don't call it "Stone" county for nothing. The thing is, I have never noticed any BSF around the big pile. Maybe I just did not know what I was looking for, but I have really never seen any thing besides normal ole house flies out there. The pile gets pretty hot down inside, maybe it is too hot for them?? I have sticky fly strips hanging down by the stables and the same thing, just normal ole house flies. the summers here are really hot, seems like it would not be too cold for them?? Any body know for sure how far their range north is?? It seems logical as stated before if they are not naturally in an area there is probably a reason and it would probably be difficult to propagate them.