Virtual Nature Trail

Scientific name: Papilio troilus
Common name: Spicebush Swallowtail

(Information or this species page was compiled in part by Deja LaJevic for Biology 220 at Penn State New Kensington in Spring, 2001)

The spicebush swallowtail is one of the most beautiful of all the swallowtail butterflies. It is a common species but is seldom found in large numbers in any given ecosystem. Its range includes the eastern half of North America from southern Canada to southern Florida west to central Texas and Oklahoma. It becomes less and less common as one moves west of the Mississippi River but is represented by "stray" populations as far west as Colorado and North Dakota and as far south as Cuba.

Appearance and Protection
The butterfly life stage of the spicebush swallowtail has a wingspan of four up to nearly six centimeters. The upper surface of the forewings is primarily black with series of small yellow spots in a narrow row along the edges. These spots continue down onto the predominately black hindwings. The central areas of the hindwings have blue scales in the females and blue-green scales in the males. The lower edges of the hingwings have the "tails" that extend out from the wing margin just laterally to the red "eye-spots." The tails and the eyespots are thought to be mimics of "antennae" and "eye" structures that function to confuse predators (mostly birds). An attacking bird is likely to grab onto this false "head-end" (you can observe many spicebush swallowtail butterflies with missing "tails" and lower wing sections. These individuals are damaged but still capable of flight!) thus sparing the more vital sections of the butterfly and making escape at least possible.

Preferred habitats for the spicebush swallowtail include open woods, forest edges, wooded swamps, pine barrens, and old fields located next to wooded areas. As the discussion of their life cycle will show, there are several plants that are preferred as food and habitat by the spicebush butterfly's developing larvae. One of the following species of plants is almost certain to be present in forested sites that maintain spicebush swallowtail butterflies: spicebush (Lindera benzoin), sassafras (Sasafras albidum), camphortree (Cinnamomum camphora) or red bay (Persea borbonia). 

Life Cycle
In a typical year, there are three sequential generations of spicebush swallowtails in our Nature Trail ecosystem. The first two of these generations include the adult, butterfly life stage (the first in April or May and the second in August or September). The third generation pauses as over-wintering, cocooned pupae that will emerge as adults the following spring. 

After mating, the female spicebush swallowtail lays a single, greenish, one millimeter diameter egg on the underside of leaves on one of the preferred plant species (listed above). After three or four days the egg darkens and its wall begins to thin. The emerging larvae are very small (less that 1/32 of an inch long) and bronze in color. The move out to the leaf margin and begin to feed on a path from the edge to the center of the leaf. The leaf is folded and secured with silk to make a tubular refuge within which the larva will pass the day-light, non-feeding hours. As the larva grows and molts, it will make larger leaf refuges that are also folded and secured with silk. Early larval instars are blackish green, bumpy, with black spots and resemble bird dropping. Later instars are smoother, and light green with some white areas and black spots. The last larval stage is bright green, very smooth, with a pale, lateral, yellow body line underlined by a fine black edge, and a prominent array of six blue dots across its abdominal segments. It also has a pair of tan, false eye spots with large black centers at the rear of the thorax, and a pair of smaller tan eye spots at the front of the abdomen. When disturbed, the larva assumes a posture that, along with its colorations has been variously likened to that of a striking snake or a tree frog. The startle effect of this behavior and display is thought to be a potential defense against predation. 

When the caterpillar is ready to pupate it changes from a green to yellow and spins its encasing chrysalis. Summer chrysalises are green while the over-wintering chrysalises are brown. It takes approximately one month for the cycle of egg to pupae to occur. It then takes approximately three weeks for the summer pupae to undergo their adult metamorphosis. 

The abundance of spicebush and sassafras on our Nature Trail has generated an extremely favorable habitat for these beautiful butterflies. Their emergences in the spring and throughout the summer add greatly to the beauty and biological diversity of our Nature Trail ecosystem.

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This page was last updated on June 30, 2014  

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