Sorry for the poor picture, it was on the outside of a window at work. This is in St. Louis, MO. Nobody had ever seen this before, but it had a tall sharp looking spine down the middle of its back. It was also quite large, at about 1.5-2" long and .75-1" wide.
This is a Wheelbug. Very interesting creature.
http://bugguide.net/index.php?q=search&keys=wheelbug&search=Search
I agree with Kwanjin, a very interesting bug. A caveat though, their bite is extremely painful and can take a very long time to heal. They are for the most part non-aggressive and only bite when cornered. They are considered a beneficial garden insect.
http://www.dogbreedinfo.com/bugs/wheelbug.htm
I've never seen one here but they're very cool looking.
