Queen Anne's lace (Daucus carota) is the common wildflower of summer. Queen Anne's lace is the wild form of the carrot you buy at the grocery store, both are Daucus carota. Look closely at the center of the flowering head and often there is a single purple floret in the center. Nobody really knows why Daucus carota has this purple flower, I can suppose it's a display to mimic an insect and make other insects think there's something good here. The real insect on the flower is a Japanese beetle (Popillia japonica).
Link to Daucus carota:
Link to Japanese beetle:
Picture taken at Prophetstown State Park, August 9, 2009.
As the flowering umbel ages, it curls into the bird's nest form you see in the flower in the background.