Live adult female fly photographed at Winfield IL USA April 23, 2004. Size: 25mm not including legs.
I believe this giant crane fly had recently been laying eggs when I stumbled upon it - the tip of the abdomen is wet as if it had been in the water or mud.
Thanks to Dr. Chen Young of Carnegie Museum of Natural History for identification of this specimen.

The small, bulbous structures are called halteres. They are used for balance and vibration damping during flight. All true flies have these organs; they evolved from the (absent in flies) second set of wings present in many other insects.