Pterourus glaucus glaucus ( Linnaeus, 1758 )

Pavulaan, Harry, 2024, Determination of a new spring-flying species of the Pterourus glaucus complex (Papilionidae) in southern New England, The Taxonomic Report of the International Lepidoptera Survey 12 (1), pp. 1-26 : 8-10

Pterourus glaucus glaucus ( Linnaeus, 1758)

Eastern Tiger Swallowtail

Status: In Rhode Island, the more southerly glaucus phenotype is not well documented by specimens, despite the widespread distribution of “Tiger Swallowtails” throughout the state, and throughout the season. However, imagery posted to various web-based resources provides adequate documentation that glaucus has a fair presence in the state, mainly during July and August, with a very widespread occurrence, but never common. It is relatively rare in spring, and is generally observed only as single individuals, never reported in multiples, as is frequent in the southeastern states, especially in summer.

In Massachusetts, glaucus is at its approximate northern limit, and is less common than near the southern New England coast, though photographic documentation shows it is present, but mainly in summer. The distinct spring form females have not been documented in available imagery. It is theorized here that perhaps glaucus is primarily a summer visitor to Massachusetts, coming north from the Connecticut and Rhode Island coastal region where a scant spring brood is documented. Any larval offspring of the summer flight in Massachusetts will likely not have enough time and host resources to complete growth before freezing weather sets in, causing larval mortality ( Tesar & Scriber, 2000). This translates to no spring flight in Massachusetts except perhaps in rare cases and more likely in the extreme southeastern coastal portion of the state, including the islands, which have a more moderate ocean-influenced winter climate. The fact that glaucus produces a canadensis -like spring form confounds identification. Only the rearing of offspring larvae of these canadensis -like forms will answer that question.

In Connecticut, glaucus appears to be well-established, though the phenogram ( Fig. 5 ) indicates a rather weak flight of the three spring-flying species ( glaucus , canadensis and “New England Tiger Swallowtail”), whereas the summer flights of the two sympatric species ( glaucus and “Mid-Summer Tiger Swallowtail”) appear to irrupt in July. This likely reflects observations of very rapid repopulation of the region from small numbers of overwintering pupae that have survived the harsh New England winter along the coast, and/or via migration from southern New York and New Jersey. [Information for neighboring regions of New York, Vermont and New Hampshire is available but beyond the scope of this study.]

Habitat: An inhabitant of virtually all types of forested or forest-associated habitats, though mixed deciduous forests contain more of a variety of documented host trees. There are few observations in Pine-dominated forest habitats. Adults are frequently found in open field habitats and suburban gardens wherever preferred nectar sources are abundant.

Larval Hosts: Black Cherry ( Prunus serotina ) is documented by observing female oviposition and by successful rearing of the larvae in Rhode Island, and appears to be a favorite host in Connecticut and Massachusetts. Tulip Poplar (Liriodendron tulipifera) is also reported for Connecticut and Rhode Island; Pin Cherry ( Prunus pennsylvanica ) and Sassafras ( Sassafras albidum ) in Connecticut. In Massachusetts, additional hosts include: Choke Cherry ( Prunus virginiana ), Beach Plum ( Prunus maritima ), Japanese Flowering Cherry ( Prunus serrulata ). Other hosts, such as Ashes ( Fraxinus sp. ) and deciduous Magnolias ( Magnolia sp. ) are certainly used but so far specific reports have not been documented in New England.

Habits: In Rhode Island, adults are almost always seen in hurried flight, though adults are fond of nectar sources and will stop to feed when the opportunity arises. As with Pterourus appalachiensis , females may spend more of their time in the tree canopy, coming down only to feed at nectar sources or to engage in courtship rituals. In Massachusetts, apparently somewhat more frequently found at nectar sources in summer.

Broods: Two broods. Confirmed early dates: April 25 (Connecticut); April 2 (Massachusetts); April 25 (Rhode Island). Confirmed late dates: August 31 (Connecticut); November 7 (Massachusetts); October 16 (Rhode Island). The early Massachusetts date is rare, and likely reflects migration arriving from the south.

Distinguishing features and variation: The largest of the northeastern Tiger Swallowtails (especially the summer forms). Wingspan of the summer form averages 3.5” (90 mm), whereas the spring form is highly variable. The females of our four Tiger Swallowtail species are more distinct from each other than are the males. Dorsally, the yellow female individuals of glaucus are readily differentiated from all other southern New England “Tiger” Swallowtails by an extensive row of blue submarginal chevrons on the dorsal hindwing ( Figs. 8 , 10 , 14 , 16 , 35 ), frequently forming into a solid blue band. In some individuals, the blue chevrons often extend onto the tornal submarginal portion of the forewing. The interior of the dorsal hindwing is generally covered by a subtle blue wash of scales. This is more evident in the black females ( Fig. 10 ) but also variably present in yellow females. Yellow females are generally more orange-yellow (ochreous) than the other “Tiger” species with the inner portion of the wings more deeply ochreous, and the outer portion being paler yellow ( Fig. 8 ).

Ventrally, the supposed diagnostic submarginal row of yellow lunules on the ventral forewing of New England female specimens are frequently enlarged into a solid band ( Fig. 17 ), thus one must rely on other features for more accurate identification. However, when the submarginal lunules are fused into a band, in glaucus the inner edge of the band is generally strongly scalloped. The ventral hindwing is broader and more rounded, and is characterized by the strongly scalloped outer wing edge. Similarly, the postmedian boundary between interior yellow (typical females) or black (form “nigra”) interior ground color and the submarginal row of blue chevrons forms a scalloped ribbon. Also, hindwing marginal lunules are shaped more like a row of crescents, frequently orange.

Males of summer generation glaucus ( Figs. 6 , 7 , 12 , 13 , 35 ) are very similar to males of the other New England “Tiger” species and can easily be misidentified. Like the females, the wings are broader, the hindwing more rounded with a scalloped wing edge, and postmedian black line similarly scalloped. Males in particular have a very broad marginal black area on the hindwing dorsum, often expanding inward to encompass nearly half the hindwing area ( Fig. 6 ).

Southern New England coastal spring individuals, similar to spring individuals of glaucus from more southerly reaches of North America, have the general appearance of summer individuals, only smaller ( Figs. 12-17 ). Some male spring individuals approach the canadensis phenotype, thus making accurate identification difficult. By contrast, the summer brood individuals ( Figs. 6-11 ) are dramatically larger. Black form “nigra” females ( Figs. 10-11 ) are undocumented in spring in New England, but are occasionally encountered in the summer brood, and mainly along the southern coastal region (Mark Schenck, pers. corr.).

One reliable way to distinguish glaucus from either canadensis or the Mid-Summer Tiger Swallowtail is to examine the first instar larvae. The larvae of glaucus are black with a single white saddle mark centered on the back.

Comments: Approximately 20 eggs were obtained from a captive female (in spring 1983). The caterpillars were raised under identical conditions as a similar larval batch (later determined to potentially be canadensis ), both on Black Cherry ( Prunus serotina ) and produced a second generation of typical summer form glaucus that same summer. The resulting adults were typical southern summer form glaucus . A female collected in Foster Center, R.I. on July 24, 2006 left a single egg which was reared through hibernal diapause and exposed to natural winter cold. The pupa was taken indoors and exposed to warm conditions in January. The resultant offspring, a female, emerged on February 19, 2007 ( Figs. 16-17 ) as a typical “southern” spring form female.

Distributional County Records: Confirmed photo or specimen records for this study. Connecticut: Fairfield, Hartford, Litchfield, New Haven, New London. Massachusetts: Berkshire, Hampden, Middlesex, Norfolk, Worcester. Rhode Island: Bristol, Kent, Newport, Providence, Washington.

Figures

Fig. 5. Combined flight pattern in Connecticut (1980-2020).

Fig. 8. P. glaucus, female. July 17, 2006. West Glocester, Providence Co., R.I. Leg. Harry Pavulaan. Dorsal view.

Fig. 10. Neotype, female, P. glaucus. Black form “nigra” (Scott, 1981). September 10, 2000. Sandbridge, Virginia Beach, VA. Leg. Harry Pavulaan. Dorsal view.

Fig. 14. P. glaucus, spring form, female. June 3, 1983. West Greenwich, Kent Co., R.I. Leg. Harry Pavulaan. Dorsal view [abdomen removed for genome research].

Fig. 16. P. glaucus, spring form, female. Ex-ova from female of July 24, 2006. Foster Center, Providence Co. Em: Feb. 19, 2007 (in lab). Leg. Harry Pavulaan. Dorsal view.

Fig. 35. Neotype (male), Papilio alcidamas Cramer 1775. September 10, 2000, Sandbridge, Virginia Beach, VA. Topotype of Pterourus glaucus Linnaeus 1758 (Pavulaan & Wright, 2002) (with same data). Dorsal (left), ventral (right).

Fig. 17. P. glaucus, spring form, female. Same data as Fig. 16. Ventral view.

Fig. 6. P. glaucus, male. August, 1992. Middletown, Newport Co., R.I. Leg. Mark Schenk. Dorsal view.

Fig. 7. P. glaucus, male. Same data as Fig. 6. Ventral view.

Fig. 12. P. glaucus, spring form, male. June 3, 1984. Great Swamp Management Area, West Kingston, Washington Co., R.I. Leg. Harry Pavulaan. Dorsal view [abdomen removed for genome research].

Fig. 13. P. glaucus, spring form, male. Same data as Fig. 12. Ventral view.