This is a Green Stink Bug. The black spots on his side are a good way to identify it. They are common throughout the U.S. and considered a pest in many places since they eat plants. This one is hanging out on a rush plant in my patio pond. I have not had a problem with them, so I think we can spare some plants for this bug.
Why are they called a stink bug? Because if you threaten them, they let out a liquid that really stinks! We got lucky with this one- I guess he didn’t think we were a threat.