Entomologists have described a new species of tiger swallowtail (genus Papilio) from eastern North America.
Papilio solstitius: (a) male, holotype and (b) female, allotype. Scale bar – 10 mm. Image credit: DeRoller et al., doi: 10.3897/zookeys.1228.142202.
Papilio is a large genus of swallowtail butterflies within the family Papilionidae.
The only representative of the tribe Papilionini, the genus includes about 200 scientifically recognized species.
The newly-identified member of the genus, named Papilio solstitius, belongs to the North American Papilio glaucus species group.
“The Papilio glaucus group is a model study system in insect evolutionary biology,” Dr. B. Christian Schmidt from the Canadian National Collection of Insects, Arachnids, and Nematodes and colleagues wrote in their paper.
“The recognition and delimitation of Papilio glaucus and Papilio canadensis as a classic sibling species pair led to three decades of study in speciation, host plant adaptation, hybridization, and molecular evolution.”
“More recently, the discovery of a third species, Papilio appalachiensis, has provided unprecedented insight into speciation via hybridization.”
“The Papilio glaucus group is part of a larger, predominantly New World clade of swallowtails of the subgenus Pterourus, sometimes recognized as a distinct genus,” they added.
“Each of the species in the group show adaptation to different thermal niches that can be broadly characterized as warm (Papilio glaucus), intermediate (Papilio appalachiensis), and cool (Papilio canadensis) climatic regions; all have broad larval host plant diets, and are not restricted by the distributions thereof.”
Papilio solstitius is closely related to these three species, but differs from all in a suite of characters.
“The most significant differences are apparent in developmental biology and phenology,” the researchers wrote.
“Papilio solstitius is unique in its long post-diapause emergence delay, with adult eclosion beginning in late June to early July, compared to May for all other species.”
Papilio solstitius’ geographic range spans the region between the northern terminus of Papilio glaucus and southern limits of Papilio canadensis.
“The core range of Papilio solstitius includes eastern and south-central Ontario, northern and central New York and adjacent Vermont, New Hampshire, and Pennsylvania, encompassing a minimum land area of approximately 174,000 km2,” the scientists wrote in the paper.
“In New York, Papilio solstitius inhabits most of the state except the southeast and greater New York City area.”
“In Canada, Papilio solstitius extends from the Montréal, Québec region west to the Bruce Peninsula of Ontario, south to the Niagara region.”
“The western limit appears to be the eastern shores of Lake Huron; we have not seen any verifiable specimens west of there.”
“Current evidence is consistent with the possibility that Papilio solstitius has a recombinant evolutionary origin similar to that of Papilio appalachiensis,” they added.
“However, most questions regarding the evolutionary origin of this species, and its role within the speciation of the Papilio glaucus-complex, remain to be answered.”
“It is our hope that recognizing and defining the taxonomic identity of this unique evolutionary lineage provides a staging point in the fertile grounds for future research.”
The paper was published in the journal ZooKeys.
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C.J. DeRoller et al. 2025. A cryptic new species of tiger swallowtail (Lepidoptera, Papilionidae) from eastern North America. ZooKeys 1228: 69-97; doi: 10.3897/zookeys.1228.142202
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