Eastern Black Swallowtail

Papilio polyxenes — the eastern black swallowtail — is one of the most familiar swallowtail butterflies in eastern North America and one of the cultural icons of NA backyard gardens. The species is widespread across all of eastern and central North America from southern Canada south through the eastern US to South America. Adults are 7-10 cm wingspan with predominantly black wings marked by two parallel yellow spot rows along the wing margins, blue dusting on the female hindwings, and small red/orange spots near the hindwing tail bases. Females are darker overall with reduced yellow markings and increased blue dusting on the hindwings — a flagship case of partial BATESIAN MIMICRY of the toxic pipevine swallowtail (Battus philenor) in the female sex. The species is the OFFICIAL STATE BUTTERFLY of Oklahoma and New Jersey. The species' major cultural significance comes from LARVAL HOST PLANTS. Unlike most swallowtails (which feed on woody host trees that backyard gardeners rarely encounter), eastern black swallowtail caterpillars feed on COMMON GARDEN HERBS — parsley, dill, fennel, carrot tops, celery, and other plants in family APIACEAE (the carrot family). The host plant restriction means that essentially every backyard garden growing these herbs is a potential breeding site for black swallowtails, and finding the dramatic GREEN-BLACK-AND-YELLOW STRIPED CATERPILLARS on garden parsley plants is one of the most-shared backyard nature discoveries in eastern North America. The caterpillars also have a distinctive defensive structure called the OSMETERIUM — a forked orange organ that protrudes from a slit behind the head when the caterpillar is threatened. The osmeterium releases a foul-smelling chemical that deters bird and small-mammal predators. The combination of bright warning coloration, conspicuous osmeterium display, and strong defensive odor makes the caterpillar one of the most dramatic chemical-defense larvae in NA Lepidoptera. Adults emerge from chrysalis after 1-3 weeks (or overwintering as chrysalis) and are voracious nectar feeders on a wide range of garden flowers, especially milkweed, butterfly bush, and zinnias. The species is harmless to humans and a major beneficial pollinator across eastern North America.