I didn't plant parsley this year, just let last year's plants come back from the root. I didn't even cut it, just watched it grow and bloom. This morning, after fierce rains, I found these caterpillars munching on it. I've seen them in years before and watched them strip the parsley down to the stems. Usually by the time I see the caterpillars it's so late in the season that the parsley is tough and bitter anyway, so I leave them. Besides, they're pretty.
I googled them and discovered they're the caterpillars of the black swallowtails we enjoy around here so much, so I'm glad I didn't smush 'em.