I get more questions about ribbon snakes than I do about anything else on this site, and I suspect that this article gets more attention than the others do. It seems to me, then, that I should write some more about ribbon snakes, even if I don’t keep any in captivity at the moment. (It’s too hard to get a reliable supply of feeder fish where I live.)
Being able to tell the difference between a garter snake and a ribbon snake is one question that crops up among field naturalists. In much of eastern North America, Common Garter Snakes, Thamnophis sirtalis, and Eastern Ribbon Snakes, Thamnophis sauritus are the only two species of Thamnophis found in the wild. Telling one from the other is therefore of some interest.1
Experienced field herpers can usually tell species apart on sight; after a while, we acquire a “search image” — we know almost intuitively which characteristics distinguish one species from the other. Sometimes it’s hard to put into words: “It’s a ribbon snake. I just know it is. I’ve seen zillions of them. Just trust me.” We forget, in other words, the characteristics that told snakes apart.
I’ve consulted my collection of field guides to find out how they tell the difference between ribbon snakes and garter snakes. Each of them cites one or more of the following characteristics to identify ribbon snakes:
- A thin body. Garter snakes’ bodies are described as “stockier” when compared to ribbon snakes.
- A long tail. Ribbon snakes’ tails are one-third or more of their total length; garter snakes’ tails are generally one-quarter or less of their total length.
- Narrower heads than garter snakes’ heads.
- Side stripes on the third and fourth scale rows. Most garter snakes have their side stripes on the second and third scale rows; some have them on the second, third and fourth scale rows.
- Unmarked labial scales. Ribbon snakes’ lips are pure white; garter snakes have dark marks along the edges of each labial scale.
- A white spot in front of the eye; garter snakes don’t have one.
The problem with many of these characteristics is that they’re comparative: it’s hard for novices to know what a thinner body, a longer tail or a narrower head is if they have no idea what a thicker body, a shorter tail, or a wider head looks like, and don’t have one to compare it to. (A similar problem exists when trying to figure out the differences between male and female snakes based on the length and thickness of their tails.) In other words, you need one of each to be able to make the distinction.
Going by tail length or general thinness is also problematic: you might have a ribbon snake with a stubbed tail, or a gravid snake instead of a garter snake, or a starving snake instead of a ribbon snake. And using scale rows only works if you can catch the snake and hold it still long enough to count them — not at all easy with squirmy little ribbon snakes!
Bottom line, it’s always easier if you can compare. Fortunately, I’ve got a photograph that will help you do exactly that.
In 2003, while taking part in a survey of a population of Spotted Turtles in and around a provincial park,2 we encountered a young Northern Ribbon Snake, Thamnophis sauritus septentrionalis, and a young Eastern Garter Snake, Thamnophis sirtalis sirtalis, in close proximity to one another:
The ribbon snake is below and facing right; the garter snake is above and facing left. You can see some of the differences: the narrower head and body, for example, and the cleaner pattern (ribbon snakes usually don’t have markings between their stripes).
But when we take a closer look at their heads, you can see even more of the characteristics that tell them apart.
As you can see, the garter snake does not have a white spot in front of its eye. And take a look at its labial scales — i.e., the scales along its upper lip: dark markings between the scales that make each scale stand out.
The ribbon snake, on the other hand, clearly has a white spot in front of its eye. (Racers also have this, by the way.) And there are no dark markings on its labial scales at all.
I think that it’s their faces, more than anything else, that make it easier to tell these two species apart at a glance. After all, garters can be skinny and ribbons can get fat (or at least pregnant), and snakes can always lose parts of their tails, but garters won’t grow white spots in front of their eyes and ribbons won’t grow dark marks along their lips.
- And it’s not like confusing the two species doesn’t occur: when I was eight years old, my mother bought me a snake from the local pet store. The tank was advertised as containing “ribbon snakes” (for four dollars each); after much examination, I figured out that it was a local Red-sided Garter Snake, Thamnophis sirtalis parietalis — hardly surprising since I was in Manitoba, and they were still being collected in large numbers at that time. But it’s not just pet stores: on page 420 of Ernst and Ernst’s Snakes of the United States and Canada, a photo supposedly of a Blue-striped Ribbon Snake, Thamnophis sauritus nitae, is clearly that of a Blue-striped Garter Snake, Thamnophis sirtalis similis.
- I wrote an article about the 2001 version of this survey.
Behler, J. L. and F. W. King. 1979. National Audubon Society Field Guide to Reptiles and Amphibians. New York: Alfred A. Knopf.
Ernst, Carl H. and Evelyn M. Ernst. 2003. Snakes of the United States and Canada. Washington: Smithsonian Press.
Harding, James H. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor: University of Michigan Press.
Holman, J. A. et al. 1999. Michigan Snakes. East Lansing: Michigan State University.
Hunter, M.L., A. J. K. Calhoun and M. McCollough, eds. 1999. Maine Amphibians and Reptiles. Orono: University of Maine Press.
MacCulloch, R. D. 2002. The ROM Field Guide to Amphibians and Reptiles of Ontario. Toronto: McClelland & Stewart.
Tennant, Alan 1998. A Field Guide to Texas Snakes. 2nd ed. Houston: Gulf.
——— and R. D. Bartlett. 2000. Snakes of North America: Eastern and Central Regions. Houston: Gulf.
Werler, John E. and James R. Dixon. 2000. Texas Snakes: Identification, Distribution, and Natural History. Austin: University of Texas Press.