This is the caterpillar for an Eastern Tiger Swallowtail, a huge yellow and black butterfly commonly seen in my garden.
They devour the curly parsley that I plant just for them. I sow several pots of parsley every spring and let the flower heads self-sow sporadically throughout the summer to keep the caterpillars well supplied. I've never found them on my flat leaf parsley. Curly parsley grows well in hot, dry spots. If you give it too much waer, it will rot.
'Roguchi' clematis are beautiful purplish-blue bell shaped clematis that bloom all summer.