I am in East Central Iowa. We typically get some for a short period each year, but this number and duration is unusual. They are more common closer to the Mississippi R. Perhaps the very wet spring influenced it. I think this is the same type of gnat they call black flies up around the lakes...
I am starting with 50 pasture raised broilers in Iowa. When we moved them to the New Terra Farm style chicken tractor at 3 wks the gnats (aka black flies) attacked them so relentlessly that they were picking themselves bare and bloody. The birds piled up in the corner and I lost 20 in less...