The trouble with rat snake taxonomy

So I went back to the CNAH website to see what changes have been in the offing in terms of snake taxonomy, because, if you know the CNAH, there will be a whole bunch of changes, some of which will leave you scratching your head. But, even knowing that, I was absolutely flummoxed by what’s been happening to the taxonomy of North American rat snakes over the last five or six years.

When I last checked, there was a Russian research paper that tried to reassign snakes of the notoriously polyphyletic genus Elaphe into new genera; North American Elaphe — corn, rat and fox snakes — were assigned to Pantherophis, with one Central American species going to Pseudelaphe. (Prior to that, three former Elaphe species had been split off into Bogertophis and Senticolis, but this is not considered to be controversial.)

But that’s really only step three (or so) of the massive amount of species renaming and reassigning that has been inflicted on North American corn, rat and fox snakes over the past two decades. Ready? Here we go.

1991: The two subspecies of fox snake are elevated to full species status: the Western (E. vulpina) and Eastern (E. gloydi).

1996: The Great Plains Rat Snake is elevated to full species status (E. emoryi).

2000: Never mind the five, easily distinguishable-by-sight subspecies of Eastern Rat Snake (Elaphe obsoleta); according to one study of mitochondrial DNA, there are, in fact, three distinct species, separated by the Appalachians and Mississippi River, that, presumably, can only be told apart by mtDNA analysis: E. alleghaniensis, E. obsoleta and E. spiloides. For the life of me, I don’t know which ones my rat snakes belong to.

2002: A population of corn snakes in the Texas-Louisiana area is elevated to full species status, E. slowinskii. As noted earlier, North American Elaphe become Pantherophis (with concomitant Latin changes, so P. guttatus instead of E. guttata, P. obsoletus instead of E. obsoleta, P. vulpinus instead of E. vulpina).

2007: But wait! Another mtDNA study argues that Panetherophis is a synonym of Pituophis. That’s right: all North American rat snakes are now in the same genus as bull, pine and gopher snakes — i.e., it’s Pituophis guttatus, not Pantherophis guttatus.

2008: Actually, never mind. An alternative classification removes rat snakes from Pituophis. But instead of restoring things to the pre-2007 status quo, three new genera are created: Mintonius for fox snakes (e.g. Mintonius vulpinus), Scotophis for eastern and Baird’s rat snakes (e.g. Scotophis obsoletus), and Pantherophis just for corn and Great Plains rat snakes.

Pardon me, but this is nuts.

In less than a decade, the Eastern Rat Snake — one of the most commonly encountered species in the eastern U.S., and one of the most popular pet snake species — has had its Latin scientific name changed or reorganized four times. The Corn Snake — the most popular pet snake in the world — has, in the space of twelve years, been split into three species and had its genus changed three times. How many times do we have to change the labels on our cages?

In addition, not only is there a certain amount of back-and-forth — from Pantherophis to Pituophis and back, for example — but many of the changes seem to be incomplete steps. Elaphe isn’t monophyletic, so we create Pantherophis — but then we synonymize it with Pituophis, until we don’t. I expect that there will be more changes as more research is done on other, related taxa — kingsnakes, milk snakes, glossy snakes, longnose snakes.

And this still presupposes that reorganizing taxonomy solely on the basis of mtDNA is something that’s going to hold up over time.

Honestly, folks, I don’t mind changes to taxonomy, but it’s kind of hard to keep up. Would you mind terribly holding off on making so many changes until you’re sure of what you’ve done — say, a decade after the initial research?