Zebra Swallowtail

Eurytides marcellus — the zebra swallowtail — is one of the most distinctive butterflies in eastern and central North America and the official state butterfly of Tennessee (designated by the state legislature in 1995). The species is widespread across the eastern US from Florida north to southern New England, west to eastern Texas and the Great Plains. Adults are 6-10 cm wingspan with the species' defining features: pale cream-to-white background wings crossed by bold black-to-dark-brown vertical stripes (the source of the 'zebra' common name), and dramatically elongated hindwing tails — ~3 cm long, the longest tail extensions of any North American swallowtail butterfly. The species is the only North American representative of genus Eurytides (which has greater diversity in the Neotropics). The species' caterpillar host plant specificity is unusually narrow even by butterfly standards: caterpillars feed EXCLUSIVELY on pawpaw (Asimina triloba) and other Asimina species — the only native temperate North American fruit-bearing trees in family Annonaceae. Pawpaw is the largest native edible fruit-bearing tree in temperate North America (fruits 5-15 cm long, banana-mango flavored), and the zebra swallowtail is entirely dependent on pawpaw distribution. Where pawpaw groves are healthy, zebra swallowtails are present; where pawpaw has been lost (especially through deer browsing pressure that has eliminated pawpaw understory in many eastern US forests), zebra swallowtails are absent. The species is therefore a useful indicator species for native pawpaw forest health. Caterpillars also sequester acetogenin compounds from pawpaw leaves, making adult butterflies bird-aversive. The species has multiple seasonal forms differing in size and tail length: spring brood is smaller with shorter tails, summer brood is larger with longer tails. The zebra swallowtail is a flagship of pawpaw conservation programs across the eastern US.