Butterfly on coreopsis tickseed. This tall coreopsis spreads very quickly by dropping seeds everywhere, but it is easy to pull up unwanted seedlings as the roots are shallow. The flowers bloom for weeks, and look nice next to my Alaska Shasta daisies, but do need deadheading and can look floppy/messy later in the season because the stalks are lanky and floppy. I put them among stronger-stemmed flowers to help keep them upright.

What kind of butterfly is this? Swallowtail?