The Anise Swallowtail, Papilio zelicaon (family Papilionidae), is a common swallowtail butterfly of western North America.  It is found in fairly open country, most likely seen on bare hills or mountains, in fields oar at the roadside.  Adult females lay eggs singly on the underside of host plant leaves.  In the first two instars, the caterpillar is a bird poop mimic – dark brown, almost black, with an irregular white band at its middle.  After that it becomes more green at each successive molt until, in the fifth (last) instar, it is predominantly green, with markings in black, orange, and light blue.  Its major food plants are members of the carrot family, Apiaceae (including Angelica), and also some members of the citrus family, Rutaceae.  
Anise Swallowtail caterpillars feed on plants in the Apiaceae family, including fennel, parsley, carrots, and dill, as well as poison hemlock.  They also use native plants like Angelica, Cow Parsnip, and Yampah.  Sweet orange (Citrus sinensis) is the only known non-Apiaceae host plant, likely because it contains similar chemical compounds.