Parsley is definitely a major attractor for this species, and dill seems to be even more so. One advantage of parsley however, is that it's more robust and not quite as sensitive to heat and drying out. Also, I've found that the caterpillars are more prone to chewing the dill plants right down to the ground (although, they'll sometimes do that to parsley as well). Ideally, it's great if the butterflies don't begin laying eggs until the plants have a had a bit of time to grow, but this year, I started finding caterpillars on the seedlings before I'd even transplanted them from the starter trays!