Adults emerge in the spring and seek host plants. Females lay round, yellow to cream colored eggs on the leaves. Caterpillars hatching from eggs are initially black with a white saddle. After molting several times, each larvae transforms into a pale green chrysalis that is suspended from a plant stem by a thread. Caterpillars have chewing mouthparts.
Adults have siphoning mouths.
This caterpillar is bad tasting to birds and other predators because of toxins absorbed from the host plants. Like other larvae of swallowtail butterflies, parselyworms have a defensive structure, called an osmeterium , right behind the head. This structure is usually concealed. It emits a strong odor that is apparently distasteful to predators. This butterfly is easy to attract and raise by planting dill or fennel in your vegetable garden.