Eastern, Black swallowtail, American swallowtail, Parsnip swallowtail
Papilio polyxenes, the (eastern) black swallowtail, American swallowtail or parsnip swallowtail, is a butterfly found throughout much of North America. An extremely similar-appearing species, Papilio joanae, occurs in the Ozark Mountains region, but it appears to be closely related to Papilio machaon, rather than P. polyxenes. The species is named after the figure in Greek mythology, Polyxena (pron.: /pəˈlɪksɨnə/; Greek: Πολυξένη), who was the youngest daughter of King Priam of Troy. Its caterpillar is called the parsley worm because the caterpillar feeds on parsley.
The Papilio polyxenes demonstrates polyandry and a lek mating system, showing no male parental care and display sites. Females are therefore able to choose males based on these sites and males are the only resource the females find at these sites.
Papilio polyxenes are found from southern Canada through to South America. In North America they are more common east of the Rocky Mountains. They are usually found in open areas like fields, parks, marshes or deserts, and they prefer tropical or temperate habitats. It is possibly extirpated from Cuba.
Male butterflies secure territories to use in mate location and courtship. These territories contain no significant concentration of nectar sources, larval host plants or night settling sites. Once secured, a male will maintain exclusive use of a territory 95% of the time. Males will aggressively chase other males who approach their territory, and then return to their territory. Success in defending a territory depends on the number of competitors and his previous success, but the size of the male is not a contributing factor. Males that emerge early in the brood are more likely to defend a female-preferred territory. These males will have early access to available territories, and will choose the ones that are most preferred by females. What makes a territory desirable by females remains unknown, and is only measured by the number of aggressive encounters between males and the overall mating frequency at these sites.
Male territories are generally of high relative elevation and topographic distinctness. This feature serves as an advantage to the lek mating system described later, as males will be concentrated in predictable locations and will be easy to encounter by females.
Females lay single eggs on host plants, usually on the new foliage and occasionally on flowers. The eggs stage lasts 4–9 days, the larval stage 10–30 days, and the pupal stage 18 days. The duration of these stages may vary depending on temperature and the species of the host plants.
Feeny et al., 1985 finds that survival of eggs and larvae of P. polyxenes varies depending on the location (near Ithaca, New York) where the eggs were laid. Eggs laid on wild carrot or parsnip plants were more likely to survive to the fifth instar than were eggs laid on poison hemlock. Eggs laid on plants at elevations of 300 to 435 metres (984 to 1,427 ft) above sea-level were more likely to survive than eggs laid at 120 meters above sea-level. There were also significant differences in survival rates between early and late broods in a year, and between years. In all cases, the primary cause of mortality was predation.
Members of the black swallowtail are long lived compared to other butterflies that inhabit temperate zones. They encounter little predation and are quick and agile if they are disturbed. However, mortality from predators will occur during roosting and during unfavorable weather due to the associated increase in predation. Adult butterflies are at the highest risk for predation when they are incapable of flight or are starved from poor weather.
In previous studies, nearly 80% of successful courtship flights were confined to a male's territory. Because a preferred territory site is crucial in mating success, males are extremely aggressive in maintaining their territory. Black swallowtails have a 4:1 male biased sex ratio, and a low female mating frequency which leads to intense male-male competition.
