This was supposed to be a Swallowtail....but, you know how that goes....
Dash inside to get the camera, and your
Kodak Cannon moment is gone.
So this is a Cabbage White Butterfly, also commonly known as a Cabbage Moth, but apparently it isn't the true Cabbage Moth, but does as much damage.
That's today's snippet of knowledge for you.
White Cabbage Butterfly Moth thingy on the Liatris
Bug catchers extraordinaire
Great white hunter