Why Isn't the Canebrake Rattlesnake its own Species?

9/2/2026

Canebrake Rattlesnake from North Carolina | © Yinan Li

The Controversy

Oh boy, what a firestorm this subject can become. I get asked this question all of the time though, and well, I guess I must address it. Why do I, and the majority of herpetologists, not consider the Canebrake Rattlesnake to be its own species when many snake "experts" do? To set the stage, the Canebrake Rattlesnake is currently considered a variation of the Timber Rattlesnake found along the coastal regions of the southeastern US from Virginia to Texas. For a long time, they were considered a seperate subspecies from the "nominal" Timber Rattlesnake. When I say "nominal" I am referring to the subspecies that the type specimen of the Timber Rattlesnake once belonged to. It may be confusing as there were two subspecies of the Timber Rattlesnake, and the "Timber Rattlesnake" was the name for one of the subspecies as well. So, when I say "nominal", I am referring to the snakes that reflect this outdated, "Timber Rattlesnake" subspecies. At one point the Canebrake Rattlesnake was suggested to perhaps be its own species, and traction for this idea seemed unstoppable. Studies found they differed not just in appearance but also venom structure and habitat. The more we learned, the more different these animals seemed to be. So, why did the Canebrake not just get shot down as a species, but as a subspecies as well?

What is a Species?

I have mentioned before that species do not exist. Species are labels we put on populations. What are the lines? Well, that is arguable in each situation. There are several species concepts and none of them work universally. That said, I think nearly all biologists can agree that species should be a monophyletic lineage, otherwise there is nowhere to draw a line in the first place. Dogs were for a long time considered a subspecies of the Gray Wolf. They were only elevated to a species when we could determine that the lineage of Gray Wolves that became Domestic Dogs was a distinct lineage from the population of wild Gray Wolves we see today. This means while dogs are Gray Wolves (as one cannot evolve out of a clade) they can be seen as a different species of Gray Wolf from the wild, "modern" Gray Wolf. So, to split the Canebrake Rattlesnake from the Timber Rattlesnake, we must see the two lineages are genetically distinct from one another.

Several "Nominal" Timber Rattlesnakes (note variation) | © Tristan Clarke

So, What do the Genetic Studies Say?

Well, let's start with the venom claim. Facebook "experts" like to claim the Canebrake Rattlesnake has a different venom composition to that of the Timber Rattlesnake. But after reading and looking at the data from Varying Intensities of Introgression Obscure Incipient Venom-Associated Speciation in the Timber Rattlesnake (Crotalus horridus) (Mark J. Margres et. al) I disagree on the claim's framing. Canebrakes appear to actually have two types of venom. Some Canebrake venoms are what the study calls "type B" (hemotoxic) like we see in all nominal Timber Rattlesnakes, and others are "type A" (with a neurotoxic component). Figure 6 (shown left) is quite damning. Looking first to the map, we see the clade in yellow has specimens with "Type B" venom and are represented by blue dots as such. Specimen CH224 (southwestern North Carolina) would be considered a nominal Timber Rattlesnake while specimen KW1414 (southern Alabama) would be a Canebrake. Note they are in the same clade and share the same venom type. Now look at the turquoise clade. Specimen CH245 (Illinois) would be a nominal specimen and CH297 (Louisiana) would be a Canebrake. These snakes are closer related to one another despite these snakes having different venom types than either are to any other clade. Now look at the gray clade in South Carolina. These should all be Canebrake Rattlesnakes, but the venom type varies with each individual tested.

This shows two things (if this is all correct from the data to the interpretation): 1) Different Canebrake Rattlesnakes can have different venom types (likely due to gene flow from the nominal Timber Rattlesnake) and 2) Canebreak specimens fall all over the cladogram and not at one point we can "cut-out".

Figure 6 from Varying Intensities of Introgression Obscure Incipient Venom-Associated Speciation in the Timber Rattlesnake (Crotalus horridus) (Mark J. Margres et. al)

This cladogram does remind me a lot of another species, Modern Humans. We see great diversity in humans across the globe, yet the cladogram offers nowhere to split one group from another. We even see that snakes in warmer regions seem to have "type A" venom; just like we see skin color in humans seems to be more about a lineage's distance from the equator rather than where they fall on the Modern Human's cladogram. There are no physical divides that stop geneflow and no genetic divides. Likewise, I see Canebrake Rattlesnakes as a cultural separation of the Timber Rattlesnake. Nature selects for the differences we see in these rattlesnakes, just as it does in humans. It is not the genetics dictating the differences.

I also have another nail in the coffin for the Canebreak as a species. The snakes on the coast look very distinct from the snakes in the mountains, but in between there is a gradient. This gradient makes it hard to say the two are very different even in appearance as gene flow and traits move through the populations in the gradient (as we can see with the "type B" venom). By us suggesting these two groups are very different is essentially cherry-picking the species as a whole. Especially now that we believe that snakes in southeast Georgia and northeast Florida (Canebrake Rattlesnakes) are closer related to snakes in western Illinois (nominal Timber Rattlesnakes) than they are to snakes in South Carolina (more "Canebrake Rattlesnakes"). This is like saying you and your uncle are in the same family, but your brother (full-blood) is not. In short, a species is a population. What we call "Canebrakes" are only collectively a population, if you include all other Timber Rattlesnakes as well.

Conclusion

Canebrake Rattlesnakes are a regional variation of the Timber Rattlesnake by our current knowledge. We can't draw the line to seperate the two genetically because they are completely interwoven. If you are still in the camp that the two are so different that they must be different, you must answer: "How can we describe a species that we can't even define genetically?" or show that we can define these two genetically. Based on the genetic data here, we could argue easier for the pink, turquoise, and black clades to be a seperate species from the orange, gray, and yellow clade. I am definitely not suggesting we do that, I am just pointing out the complications with arguing that specimen CH297 should be the same species as specimen MM0020 but not the same species as CH239.

I have had someone before say, "Well if it is only genetics, why does that stop us? We described species long before we had genetics." Sure, we did; and often we were wrong. We have gone back and amended lots of taxons because genetics is a stronger window into natural history and populations than the animal's appearance.

That said, culturally I do think Canebrake Rattlesnake is distinct and we should recognize that. The differences do warrant the notes in the field guides and Virginia DWR does list the Canebrake as its own population and on a higher tier listing than the nominal Timber Rattlesnake. I think this is fair as well. It is also valuable to know where to expect snakes to have neurotoxic venom, as the side effects are quite different than hemotoxic venom alone. Who knows what medical marvels we may find in the future with this venom. One of my favorite facets of herpetology is looking at the differences between two populations of one species. I love looking at locales and noting major differences. Life is diverse and species are not just cookie-cutter organisms. My issue is not that I do not want the Canebrake to be species (I consider myself neither a splitter nor lumper), rather the current evidence suggests that speciation is not the reason Canebrakes have differences to nominal Timber Rattlesnakes.

Works Cited

Margres, M. J., Wray, K. P., Sanader, D., McDonald, P. J., Trumbull, L. M., Patton, A. H., & Rokyta, D. R. (2021). Varying Intensities of Introgression Obscure Incipient Venom-Associated Speciation in the Timber Rattlesnake (Crotalus horridus). Toxins, 13(11), 782. https://doi.org/10.3390/toxins13110782