Identification and Documentation of Tiger Swallowtails in Tennessee

One of the most exciting butterfly events of the past few decades was the discovery of a NEW species of tiger swallowtail in the southern Appalachians and its subsequent documentation. Efforts to document the distribution of the new species--Appalachian Tiger Swallowtail (Pterourus [Papilio] appalachiensis)--have proceeded rather quickly in North Carolina and West Virginia, where the species is known to occur in many high-elevation counties of each state.  Similar efforts in Tennessee have proceeded more slowly, but the situation changed dramatically during spring 2009.

    Credit for the discovery of the Appalachian Tiger Swallowtail belongs to Harry Pavulaan and David Wright, who noticed interesting distinctiveness about high elevation tiger swallowtails in the southern Appalachians while conducting research about the species of Celastrina (azures) in the same area during the period from 1985 to 2001.  Pavulaan and Wright published a paper in 2002 describing the new species of tiger swallowtail and followed that publication with another in 2004 documenting the existence of black form females of P. appalachiensis in West Virginia.  DNA studies clearly support the erection of the new species.

    Initially, Pavulaan and Wright believed that they were dealing with a form of Canadian Tiger Swallowtail (P. canadensis), but subsequent study revealed that the Appalachian Tiger Swallowtail is not a form of that species nor is it a typical hybrid; rather, it is a new species resulting from "hybrid introgression," whereby the genes of one species, Canadian Tiger Swallowtail, slowly "invaded" the genes of another species, Eastern Tiger Swallowtail (P. glaucus), over a long period of time and led to the formation of an entirely new species. The time involved for this process to take place was probably tens of thousands of years, dating back to the last ice age when Canadian Tiger Swallowtails were pushed south by ice sheets and were sympatric with Eastern Tiger Swallowtails for thousands of years in the unglaciated Appalachian highlands, occasionally hybridizing with them.  With the melting of the ice sheets, the population of Canadian Tiger Swallowtails retreated north, but in the wake of this retreat the Canadian Tiger Swallowtails left some of their genes in the population of Eastern Tiger Swallowtails, which evolved into Appalachian Tiger Swallowtails, a totally distinct species, not a hybrid form. Formation of new species in this manner has seldom been shown to occur, another interesting feature of the discovery of P. appalachiensis in the southeastern mountains.

    Before proceeding to the i.d. of the Appy, let me thank John Hyatt for providing documentation of this species in Unicoi County, where he obtained evidence of its presence during early June 2006.  I also thank Krushnemegh Kunte for providing documentation of its presence in Sevier County, where he obtained evidence during late May 2006.  These records went into the database of the Butterflies and Moths of North America (BAMONA) as being among the first documented records for Tennessee.

   Those who seek for evidence of Appalachian Tiger Swallowtail in the counties of East Tennessee other than Polk, Sevier, and Unicoi are advised to do so from late April through late June or early July, but primarily during May, when the main flight season of this univoltine (i.e., single-brooded) tiger swallowtail occurs.  It is said to be the only tiger flying above 3500 feet in Great Smoky Mountains National Park during May (D. Wright, pers. com.), and this may be true of other sites with elevations above the 3500-foot limit along the eastern border of the state.

   Quite a few subtle field marks characterize the Appy and allow separation from Eastern Tiger Swallowtail, and these are well described by Pavulaan and Wright (2002).  A big difference, if I may phrase it that way, between the two is, well, the bigness of this swallowtail compared to the Eastern, as noted in the following photo:

Two Appalachian Tiger Swallowtails (foreground) in comparison with two Eastern Tiger Swallowtails (background); note size difference, evident despite the difference in the distance to each species; also note the limited blue on the hindwing of the Appies and the lighter shade of yellow on the wings of the Applies.  Photo J. Basham in Polk County (9 May 2009).

    Appies tend to be much larger than Easterns in the areas where the two overlap, so the first clue to finding the Appy is to find really big Eastern-like swallowtails during spring and early summer; when the two species are present in the same field of view, the size difference between them is remarkable, if "normal"-sized individuals of each species are being viewed.  Also note the very limited blue on the submargin of the hindwing above of Applies and the lighter shade of yellow on both forewings and hindwings above.

    A somewhat more subtle field mark is the amount of blue in the submarginal band on the hindwing below; the extent of blue in this band is greater and somewhat more emphatic in the Appy (see Figure 1 below) than in the Eastern (see Figure 2 below), although this characteristic is not as clear-cut as might be desirable. It should be noted that a comparison of female Appy with female Eastern or a comparison of male Appy with male Eastern would make this distinction greater than is apparent below, but I was limited in the choice of photos I had available.  

Figure 1. Male Appalachian Tiger Swallowtail (P. appalachiensis) below, photographed in Great Smoky Mountains National Mark, Sevier County, Tennessee, 23 May 2006; presented with permission. Note: not life size.

Figure 2. Probable female Eastern Tiger Swallowtail (P. glaucus) below, photographed in Cane Creek Park, Putnam County, Tennessee, during August 2002; photo Stephen J. Stedman. Note: not life size.

    Efforts to document Appalachian Tiger Swallowtail in a Tennessee county other than Polk, Sevier, and Unicoi should ideally include photos of live individuals or specimens of that species next to live individuals or specimens of Easterns; photos displaying the hindwing below may also be useful.

    Good luck if you seek Appalachian Tiger Swallowtails in Tennessee, and please keep me informed about your findings.

   Acknowledgment: Many thanks to M. L. Bierly for refocusing attention on the effort to document the presence and distribution of Appies in Tennessee during the early part of the 2009 butterfly season.