This fly has an unusual pattern to its eyes, and is therefore very distinctive.  I have only run across it once, and the individual I saw was resting on a leaf.  It is a syrphid fly, and is not native to the United States, but is native to Europe instead.

It is reported that the larva feed mostly on seaweed, and that the fly is mostly found in coastal areas.  What it is doing in the middle of Iowa, I don't know.  I suspect that there are some things not known about the life cycle of this fly.