Pipevine swallowtail

Below is a picture of a Pipevine Swallowtail. This butterfly was in my backyard in Berkeley, California yesterday. I have had pipevine, Aristolochia Californica, for more than ten years, but I have never seen the associated butterfly or any caterpillars on the plant. I am very excited about this long-awaited butterfly showing up in my backyard. I have heard that the wilder areas nearby are very dry because all of the rains were so early this year. As a consequence, the butterflies are visiting watered gardens to find lush hostplants. I have no way of testing this, but it seems like a plausible explanation. I am hoping that I find eggs soon.