Keroplatus perhaps, dorsal-lateral - Keroplatus militaris -
Plymouth Rock, Winneshiek County, Iowa, USA August 4, 2008 Size: 8- mm
Woodland Malaise Trap 14-Jul-2008 to 4-Aug-2008.
The antennae look much like/similar to the drawing of Keroplatus clausus antennae in "Manual of Nearctic Diptera"