Ratsnakes Pantherophis obsoletus complex


The Pantherophis obsoletus species complex is comprised of four species of very diversely patterned ratsnakes in Eastern North America. Even within species, color pattern is variable and tied to the environments in which the individuals are found. The map below shows the approximate extent of the range of the four currently recognized species. Click on each species to learn more about it, or scroll down to learn about the historical biogeography of this species complex, how research into this complex expands our understanding of snake evolution, how these species are affected by changing climate and what you can do to help understand and protect them far into the future.


Eastern Ratsnake Pantherophis alleghaniensis

Central Ratsnake Pantherophis spiloides

Western Ratsnake Pantherophis obsoletus

Baird's Ratsnake Pantherophis bairdi

Where are the "black ratsnakes" and why is this account different from older sources?

Species names are hyptotheses that are tested and revised. The "black ratsnake" species complex, formerly Elaphe obsoleta, underwent revision in 2001-2002 from multiple authors and received two main changes. First, the complex was delimited in Burbrink 2001[Online PDF] based on what were then modern molecular methods, where three distinct lineages were uncovered that did not reflect previous subspecies designations. Each of the three geographically partitioned taxa were elevated to full species status, and subspecies were discarded. The polytypic color patterns in these species are most likely under strong selection by the local environment and don't reflect evolutionary history. Where species intersect and habitat converges, color pattern also converges, leaving these species nearly morphologically indistinguishable to the naked eye.

Second, using Elaphe as a genus name wasn't the best way to reflect phylogenetic history, so the genus Pantherophis was adopted for new world ratsnakes in Utiger 2002 [Online PDF]. These species were investigated further using genomic data, and in 2020 Burbrink et al released an update [Online HTML], clarifying ranges, filling in grey zones and testing hypotheses concerning the four distinct species. The currently accepted species in this complex are Baird's Ratsnake Pantherophis bairdi, Western Ratsnake Pantherophis obsoletus, Central Ratsnake Pantherophis spiloides and Eastern Ratsnake Pantherophis alleghaniensis.




Links for Biologists and Educators:
Shapefiles for range and habitat [.asc xx mb]
Original Research on Ratsnake Phylogeography
[Online HTML Full Text]