RED ADMIRAL IRRUPTION YEAR???
Seems Chicago is not the only place experiencing the current Red Admiral largess.
Red Admiral western New York
Red Admiral (Vanessa atalanta) do not survive northern harsh winters so only fly once a season in the north then migrate south where they can have two or three broods a year then over winter in larval stage.
The larval hosts are in the Nettle family, Urticaceae, Stinging Nettles (Urtica holosericea and U. urens) Baby's Tears (Helxine or Soleirolia) and Pellitory (Parietaria).
The larva is solitary, in a host plant rolled-leaf shelter. I saw a picture of the rolled leaf that the larva live and eat inside of on some butterfly site but can not now find it. I will be watching stinging nettles in my garden and on hikes to see if I can find a feeding larva of the Red admiral.
Google images of host plant...