Papilio troilus, the spicebush swallowtail or green-clouded butterfly, is a common black swallowtail butterfly found in North America. It has two subspecies, Papilio troilus troilus and Papilio troilus ilioneus, the latter found mainly in the Florida peninsula. The spicebush swallowtail derives its name from its most common host plant, the spicebush, members of the genus Lindera.
The family to which spicebush swallowtails belong, Papilionidae, or swallowtails, include the largest butterflies in the world. The swallowtails are unique in that even while feeding, they continue to flutter their wings. Unlike other swallowtail butterflies, spicebushes fly low to the ground instead of at great heights.
Distribution and habitat
The spicebush swallowtail is found only in the eastern US and southern Ontario, but occasionally strays as far as the American plains states, Cuba, Manitoba and Colorado.
This primarily black swallowtail is normally found in deciduous woods or woody swamps, where they can be found flying low and fast through shaded areas. Females tend to stay in open plains, while males are typically found in swamp areas. Temperature may be a limiting factor for the spread of P. t. troilus, as in experimental conditions, they do not fare well at or above nor are they capable of flourishing at or below .
Papilio troilus ilioneus
The smaller subspecies of P. troilus is confined to the Southeastern coastal United States, namely throughout Florida and along coastal Georgia and in places in Texas. Adults are primarily black/brown in color, with a trademark green-blue (male) or bright blue (female) splotch in the shape of a half moon on the hindwings. The forewing has a border of cream-colored, oval spots. In the middle portion of the wing, the spots can be moon shaped and a light blue in color. In females, the orange spot at the base of the wings will turn a greenish-white shade in summer, but not the spring.
On the underside of the hindwing, there will be a dual row of orange spots, which distinguishes it from the pipevine swallowtail, which only has a single row of spots. In between these rows, there is more blue or green coloring.
P. t. ilioneus
The distinguishing difference in color between the two subspecies is evident where the spots, which are blue in color on the hindwing of the P. t. troilus, are more yellow in color in P. t. ilioneus. Additionally, splashes of blue can trail all the way down the tail of P. t. ilioneus. Other possible host plants include prickly ash (Zanthoxylum), as well as tulip tree (Liriodendron tulipifera), sweetbay (Magnolia virginiana), camphor (Cinnamomum camphora) and redbay (Persea borbonia). However, when given the choice between spicebush and sassafras, the P. t. troilus showed no significant preference for either.
Additionally, P. t. ilioneus live only on redbay because that is the primary host plant within the Southern range. However, in a test of P. t. troilus and P. t. ilioneus on redbay, sassafras and spicebush, although the P. t. ilioneus had higher growth and survival rates on redbay than the P. t. troilus, as a holistic group, both subspecies performed better on sassafras or spicebush over time. This fact is especially noteworthy because Lauraceae are distantly related to the host plants of other species that are food for Papilio caterpillars. The fact that spicebush swallowtails live and feed primarily on Lauraceae only is noteworthy also because most other varieties of swallowtail butterflies are nowhere near as specific. Part of the reason for the selective nature of P. troilus and host plants may have to do with the requirement of positive stimuli to confirm that a plant is Lauraceae among P. troilus before they will feed on it, while P. glaucus, for example, will at once try to feed on any plant presented to it. The brown color of the larvae is independent of leaf color and will occur even on a green leaf. A folded leaf serves as the home for the young larvae. At the end of the pupating process, the larvae have become pupae which are either brown (winter) or green (summer). Once they have reached the adult stage, Papilio troilus can live anywhere from two days to two weeks dependent on resource availability and predator avoidance.
thumb|left|Larval mimicry, fourth instar
Adult mimicry
Adult spicebush swallowtails practice another type of mimicry, as they resemble the pipevine swallowtail (Battus philenor), a foul-tasting butterfly.