Another Wheel Bug

This guy has been hanging around our front door for a couple of days. I finally decided to take a photo of him. I don't know if this is the same one that was in the back yard a couple of months ago or not. I don't know how common these guys are. I had never seen one before, and now within a month I have seen two of them in our yard. I understand that they can give a painful bite. I think the wheel on the back is quite interesting!