When I meet a Red Spotted Purple Butterfly I check to see if it is fresh (recently eclosed from its chrysalis) and if it bears red spots on its forewings. On its upper (dorsal) forewings. Most of them lack prominent red spots.
I followed this one, at Raccoon Creek State Park in southwestern Pennsylvania because I saw that it had beautiful red spots at the apex (outside corner) of its wings.
For reasons yet not clear to me, I Love those red spots, and smile when I find them!
NB, Were those Georgia Asters in the background?