I believe that this is a Katydid nymph. ID welcome. If it had rested in the center of the leaf, I likely would not have noticed it. It's camo patterns nicely blend in with the leaves, but its chosen position on the leaf gave it away.
Note the long antennae folded underneath the body. When I started they were under, later shots show them hanging down, and when I finished they were tucked back under.
Breezy conditions using natural light gave me one fairly good shot out of 83. The breathing was quite noticable. It was interesting to observe under magnified liveview.
Reduced from orginal 3200x1800 crop.
Katydid Nymph on Swamp Milkweed by
Roger