Black Butterfly With Blue Spots - Limenitis arthemis
Beach Park, Lake County, Illinois, USA August 20, 2011
Looks similar to a black swallowtail, but doesn't have the characteristic "tails" on the rear wings. (Not sure if that's a normal variation, or something that may break off on an older insect.)
Photo taken at Illinois State Beach Park (North).
Markings on underside of wing are more orange than blue.