I saw an Anax junius for the first time this year on April 25th. I am pretty sure this is the same one–I took the photo today.
The common green darner migrates in a manner similar to the monarch. This individual crawled out of the water somewhere far south of here, and its offspring will leave Iowa and head south in the fall.
I have not seen a living butterfly yet this year, but I have seen a dragonfly.