I don't know how long I chased this guy around the butterfly bush before I got even this less than stellar shot. But I think its enough to call it diffinis.

Nearly as abundant as the Eastern Tiger Swallowtails on that summer weekend back home.

These guys and several of their mimics were practically rioting in my mother's back yard.

Tentatively IDed as Microthopala vittata on BugGuide but I'm not certain. This individual certainly wasn't on goldenrod.