It doesn't matter that we have butterfly bush and coneflower and Joe-pye and ironweed—if we have zinnias, that's where the butterflies are. The fact that my zinnias are all pink this year didn't bother them as much as it did me.
Even if their favorite nectar plant is zinnias, these Eastern Tiger Swallowtails fly into the trees to lay their eggs. Some of their favorites in my neighborhood are tulip poplar (Liriodendron tulipifera), wild cherry (Prunus serotina), river birch (Betula nigra), and ash (Fraxinus americana).
I understand you can tell the sex of Eastern Tiger Swallowtails by the colors on the wings, but it must take some lessons from an expert, because I can't really tell the difference at this point. The pictures used (here) for examples, look pretty much all alike to me.
There is an interesting phenomenon among females, though. They may be yellow or they may be brownish black. So if you see a brownish black Eastern Tiger, it's definitely female.
Where the Pipevine Swallowtail lives, the Eastern Tiger sometimes adopts the same dark coloration that they have. Pipevine Swallowtails are poisonous from eating Aristolochia species, so the female Eastern Tiger takes advantage of that by looking like a poisonous butterfly herself. She will be avoided by predators just the same as the Pipevines. Meanwhile, she can keep on eating what Eastern Tiger Swallowtails prefer. Clever!
Caterpillars begin life looking like a bird dropping on a leaf. Later, they turn green and develop a large head with big eye spots which may confuse predators and serve to protect the caterpillars from being eaten. When all goes well for the caterpillar, a beautiful butterfly shows up on your pink zinnia a few weeks later.
Recommended: Attracting Butterflies and Hummingbirds to Your Backyard by Sally Roth