Teresa
Dear fellow Iowan, the best guess is a Zale moth caterpillar. The photo is not clear enough for a better ID.
The size, pose and shape say it is either a Zale species or one of the underwing moth caterpillars...Catocala species, but not sure which one. Here are the possible images that have been posted on bugguide.net so far. There are others that are out there but not yet been photographed and posted. http://bugguide.net/node/view/43764/bgpage
Either one is a neat find.
The moths do come to lights on the porch, so you might look at moths on the porch with the lights on...unfortunately the moths come around between 10pm to midnight.
