According to Martin Hauser, this species was introduced to the Chicago region in 2006 from Europe. Similar species are found in Australia and Africa. They were common on this date (06/29/2011} in the forest preserve area where I photographed them and perhaps this had to do with people taking their dogs for walks there, since they feed at least partially on feces and other dead matter. I think Signal Flies got their name by the dance-like behavior that many of the species demonstrate, with their wings moving like semaphores. You can see a video of such behavior at http://www.youtube.com/watch?v=Q7b6M9ilCYQ
However, this species did not perform such a dance when I saw them, they simply lighted on sunny leaves and sat still enough to be photographed easily.