The Hackberry Butterfly is pretty uncommon around here, as it lays its eggs only on hackberry trees.  Most people have never even heard of a hackberry tree, so they don't get planted much.  I've seen the Hackberry Butterfly several times drinking sap from the leaves of my neighbor's trees before I started gardening.  Since then, I have only seen it twice.  Both times it was on a window screen.  Hopefully, one will lay eggs on my hackberry tree someday, if one hasn't done so already.