The (eastern) black swallowtail (Papilio polyxenes), also called the American swallowtail or parsnip swallowtail,^[1] is a butterfly found throughout much of North America. It is the state butterfly of Oklahoma. 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.

Description

Ventral view - female

The black swallowtail has a wingspan of 8 to 11 cm (3.1 to 4.3 in). The upper surface of the wings is mostly black. On the inner edge of the hindwing is a black spot centered in larger orange spot. A male of this species has a yellow band near edge of wings; a female has row of yellow spots. The hindwing of the female has an iridescent blue band.

In the southwestern United States, yellow forms predominate in the subspecies Papilio polyxenes coloro.

After mating, small, yellow eggs are laid, typically on plants from the carrot family, Apiaceae, including dill, fennel, Queen Anne's lace, parsley, and golden alexanders. They are also found eating rue and bishop's weed. First instar larvae grow to about 1.5 cm (0.59 in) long and resemble bird droppings. They are dark black with a white band in the middle and have spikes, with a light brown-orange ring at the base of each of the spikes in the dark region (spikes are white on the white band). Later instars grow to about 5 cm (2.0 in) and are green and black banded with yellow spots around every second black band. They have short, black spikes around some of the black bands, although these tend to disappear as the larva nears pupation.

Caterpillar and chrysalis

The black swallowtail caterpillar has an orange "forked gland", called the osmeterium. When in danger, the osmeterium, which looks like a snake's tongue, everts and releases a foul smell to repel predators.

Black swallowtail chrysalis

The pupae may be green or brown, but not depending on surroundings or the background on which they have pupated. The color of the chrysalis is determined by a local genetic balance that ensures the majority of pupae will blend in.^[2]

Similar species

• Old World swallowtail (Papilio machaon)
• Pipevine swallowtail (Battus philenor)
• Spicebush swallowtail (Papilio troilus)
• Short-tailed swallowtail (Papilio brevicauda)
• White admiral (Limenitis arthemis)

Photogallery

• 

  Laying eggs on parsley

• 

  Eggs on parsley

• 

  First instar caterpillar in northeast Georgia

• 

  These second- or third-instar larvae in northeast Georgia still have spikes.

• 

  Late-instar caterpillar (without spikes) soon ready to pupate

• 

  Osmeterium visible after slight provocation

• 

  Caterpillar color variations

• 

  Greenish-brown chrysalis

• 

  Ventral view with chrysalis

References

• Eastern Black Swallowtail Butterfly: Large format reference quality (free) photographs Cirrus Digital Imaging
• "Papilio polyxenes". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=188543. Retrieved 6 February 2006. 
• Burris, Judy; Richards, Wayne (2006). The Life Cycle of Butterflies. Storey Publishing. pp. 20–21. ISBN 978-1-58017-617-0. 
• Darby, Gene (1958). What is a Butterfly?. Chicago: Benefic Press. p. 36. 

This article is adapted in part from this page at the USGS Northern Prairie Wildlife Research Center.