Dark and Beautiful

I always get the dark butterflies mixed up. Three in this area are similar:

Pipevine Swallowtail (Battus philenor),
Spicebush Swallowtail (Papilio troilus) and
the black form female Eastern Tiger Swallowtail (Papilio glaucus).

But I think this one is the latter.

The plant she's on is White crownbeard (Verbesina virginica). (It's the same as Frostflowers plant from back in February.)

It's curious that only some Eastern Tiger Swallowtail females are dark - to mimic the poisonous Pipevine Swallowtail - and some are not. They seem to have several successful strategies to avoid getting eaten: the young caterpillars resemble bird droppings, the mature caterpillar has large false eyespots, and the chrysalis looks like a stick. So why after all that trouble, wouldn't you want to turn black and look poisonous?

Maybe the male butterflies prefer blondes.