Mating Black Swallowtails. Papilio polyxenes. When I first saw this, I though it might be a hanging dead butterfly, all torn up from the vicissitudes. Always double-check the anomalies!
Interestingly, this pair attracted another male, if not more than one over the ten to fifteen minutes I was there. (Black Swallowtails are all over.)
The second male really wanted in on the action.
Does this work?
Bonus Swallowtails:
The female Black Swallowtail. She lays her eggs on many members of the parsley family (Apiaceae).
The male Black Swallowtail.
This is a male Spicebush Swallowtail, missing some of his hindwings. Papilio troilus. The Black Swallowtails are all over Green-Wood, but this is a rarer butterfly there — this is the only one I’ve seen this summer so far. No photograph of a female at present. The female lays her eggs on spicebush, sassafras and other laurels (Lauraceae).
Backyard and Beyond 
“all torn up from the vicissitudes.” Nice!
Whence the name “swallowtail”?
The trailing tails of their underwings evidently reminded someone of the (Barn) Swallow.