Spot the cottonmouth

 by Greg Mayer

Last month I took a trip, and posted a “spot the _____” post for an animal I’d seen and photographed, but without giving any geographic location clues, so as to make identification more challenging. Despite this, many readers were not only able to spot it (not very hard), but also identify it: a cottonmouth. It is, more specifically a western cottonmouth (Agkistrodon piscivorus leucostoma), and I photographed it in the Cache River State Natural Area in southern Illinois. Here she is again, in a slightly different view. You can see she’s right in the middle of the footpath, and blends in fairly well with her background. By the time this photo was taken, she was pretty agitated and had reared up, so she stood out more.

A western cottonmouth (Agkistrodon piscivorus leucostoma) on Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016.

A western cottonmouth (Agkistrodon piscivorus leucostoma) on Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016.

Southern Illinois is very interesting from a natural history point of view, both geologically and biologically. The southern part of the state narrows to a point where the Mississippi and Ohio rivers join. A bit north of their confluence you find a set of hills crossing the state from west to east, called the Shawnee Hills or “Illinois Ozarks“. Illinois is otherwise exceedingly flat (in Wisconsin, Illinoians are know as “flatlanders”, and considering how flat Wisconsin is, that’s saying something), so the Hills are a distinctive landscape feature. Composed of Carboniferous sandstones and limestones from the mid-Paleozoic epicontinental sea that covered what is now the middle of the U.S., differential erosion has created many interesting land forms, including Camel Rock and Giant City.

Biologically, many southern species reach the northern limit of their range in southern Illinois. (Culturally, too– having driven several times from Chicago to the Gulf coast in Mississippi, I can attest that you enter the Bible Belt somewhere in southern Illinois, and leave it about ten miles north of the Gulf of Mexico.) In the Hills you get a high diversity of oaks (my favorite trees), but just south of the Hills you enter the flat Cache River country full of cypress and tupelo swamps, two species at the northernmost edge of their ranges. The Cache River itself is a remnant of an old bed of the Ohio River.

A large, old, bald cypress (Taxodium distichum) at the Big Cypress Access Area, Cache River State Natural Area, Illinois, USA, March 23, 2016.

A large, old, bald cypress (Taxodium distichum) at the Big Cypress Access Area, Cache River State Natural Area, Illinois, USA, March 23, 2016.

The giant old cypress above is said to be 1000 years old, with a basal circumference of 43 feet (13 m). A couple of buttresses from a second very large cypress can be seen at the right; that tree is known as the “Winnie the Pooh Tree“. Cypresses are known for having upward projections from their roots that stick above the water, known as “knees”; their function is unclear.

A cypress "knee", Big Cypress Access Area, Cache River State Natural Area, Illinois, USA, March 23, 2016.

A cypress “knee”, Big Cypress Access Area, Cache River State Natural Area, Illinois, USA, March 23, 2016.

My wife and I spent one day hiking in these swampy areas in a few different places, and were well rewarded by our hike along the edge of Little Black Slough, a tupelo/cypress swamp.

Bald cypress and water tupelo (Nyssa aquatica) in Little Black Slough, alongside Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016

Bald cypress and water tupelo (Nyssa aquatica) in Little Black Slough, alongside Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016

We saw and photographed a bald eagle– it looked much better through binoculars!

Bald Eagle (Haliaetus leucocephalus) perched on top of bare tree across Little Black Slough from Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016. If Stephen Barnard had taken this photo, you would be able to read the number on the eagle's leg band.

Bald Eagle (Haliaetus leucocephalus) perched on top of bare tree across Little Black Slough from Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016. If Stephen Barnard had taken this photo, you would be able to read the number on the eagle’s leg band.

After 3 days of hiking, our herpetological findings had been limited, just a few true frogs and painted turtles. Southern Illinois is the northern edge of the range for cottonmouths and copperheads, but I had begun to think the season was not far enough advanced to have a chance to see them. At 3:30 in the afternoon, when basking was likely to be done for the day even if the snakes were active, I thought our snake chances were over.

Hiking along Tupelo Trail, Little Black Slough to the right, Cache River State Natural Area, Illinois, USA, March 23, 2016

Hiking along Tupelo Trail, Little Black Slough to the right, Cache River State Natural Area, Illinois, USA, March 23, 2016

Just moments after the photograph above was taken, the photograph below was taken. My wife had stepped over or next to the snake. A pace behind her, I saw it—a thick bodied, banded snake, right next to the water—and I immediately thought “water snake or cottonmouth?” I changed my step in mid-stride, awkwardly hopping over the snake and turning to face it– no doubt, it was a  cottonmouth!

A western cottonmouth (Agkistrodon piscivorus leucostoma) on Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016.

A western cottonmouth (Agkistrodon piscivorus leucostoma) on Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016.

It too had turned to face me, and raised and pulled back its head, opening its mouth and exposing its “cotton” mouth. In the picture below, you can see several neat feature of the snake’s biology. First, is the aforementioned open-mouthed threat display, enhanced by the mouth color. Second, note the eye, divided into dark and light halves, that break up its identifiable shape, helping to camouflage the snake. Between the eye and the lip, note the white pit, which is an infrared sensitive structure which enables the snake to get a “thermal picture” of its environment, and the thing from which “pit vipers” get their name. Pit vipers can strike a warm object accurately using only their pits to locate the object. And finally, the fangs are in the long folds of the buccal mucosa alongside the lips on each side of the mouth. The fangs can pivot, and would swing forward out of the surrounding tissue when the snake actually tried to bite, either for predation or defense. (Click on these photos to enlarge them and see more details.)

A western cottonmouth (Agkistrodon piscivorus leucostoma) on Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016.

A western cottonmouth (Agkistrodon piscivorus leucostoma) on Tupelo Trail, Cache River State Natural Area, Illinois, USA, March 23, 2016.

I took these pictures with a Nikon camera I had gotten for Christmas, and was pleased to find you could actually see the blood vessels in the snake’s mouth, but I was too unfamiliar with it yet to figure out in the moment how to take video. So, my wife used her cell phone.

Note the vigorous “rattling” of the tail– many snakes do this, not just rattlesnakes. Against the substrate and dry leaves, this can be quite noisy, and in a cottonmouth acts as another threat beyond the white, open mouth display. Rattlesnakes have taken this further, with the loose fitting, keratinous, rattle scales at the tip of the tail capable of making a loud buzzing sound. In the video I mention the “quite long” tail to note the smooth tapering of the tail from the cloaca, indicating this is a female. Having said that, I immediately realized that to most people it would seem that the tail is shorter than they expected, so I then say it is a “fairly short” tail. The two statements are not contradictory– just pointing out different aspects of the snake’s tail: the tail shape showing its sex, but also that, as in most snakes, the tail is relatively short compared to the body length.

A natural history tour of this area of Illinois is well worthwhile, with many state and federal protected lands. The one criticism I would make is that in most areas the interpretive materials (i.e. signage) are sparse to lacking. There is, however, a fine, small museum run by the state of Illinois, the Barkhausen Cache River Wetlands Center, and I would recommend beginning a hiking tour with a couple or more hours there first.


Greene, H.W. 1997. Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley. (excellent general natural history of snakes that we’ve had occasion to recommend here before)

Smith, P.H. 1961. The amphibians and reptiles of Illinois. Illinois Natural History Survey Bulletin 28:1-298. (details on Illinois herpetofauna)

 

22 Comments

  1. rickflick
    Posted April 12, 2016 at 9:14 am | Permalink

    Thanks for the tip – visiting S. Illinois – this makes Chicago seem like a minor distraction.
    It’s nice to keep in mind the many natural history sites around the country when you travel. I hope to include them in my plans whenever I can.

  2. Posted April 12, 2016 at 9:15 am | Permalink

    Wonderful post Greg and thanks for the plug for my Snakes book! A few postscripts in case they’re of interest: 1) It’s typical that your Cottonmouth does NOT have her fangs protracted (unlike Old World viperines in a gaping threat display)–if she did, they’d block her “pit vision.” 2) These are SMART snakes–one was seen “trap-lining” somebody’s pitfall bucket array, going from trap to trap, suspending by tail and looking for frogs in the bottoms of the buckets. 3) For all their awful reputations, Cottonmouths are remarkably unlikely to actually bite unless restrained. Among my very favorite snakes!

    • Dominic
      Posted April 12, 2016 at 9:52 am | Permalink

      I asked below, if they can re-grow a broken tooth or would that mean the end of the snake through starvation?

      • Posted April 12, 2016 at 9:58 am | Permalink

        Vipers always have replacement fangs “in the wings,” so loosing one is no big deal…

  3. Ken Phelps
    Posted April 12, 2016 at 9:15 am | Permalink

    The function of Cypress knees is to help woodworkers and boat builders. Blessed be the Designer.

    • GBJames
      Posted April 12, 2016 at 9:25 am | Permalink

      👍🏼

    • ChrisB
      Posted April 12, 2016 at 10:39 pm | Permalink

      A botanist once told one hypothesis for cypress knees was that they improved gas exchange with the atmosphere, since much of a cypress’s root system is submerged. I wonder if the knees provide enough surface area to perform that function.

  4. Blue
    Posted April 12, 2016 at 9:37 am | Permalink

    Compelling post … … my thanks, Dr Mayer !

    Fascinated by all serpentines, I of the Midwest USA am particularly gratified to read within it the northern – like boundary areas of certain of the Northern Hemispheric snakes !

    I have trouble enough merely waltzing along without clumsily stumbling off of curbs and sidewalk edges — and falling down ! (as actually occurred on m’stroll in to work just this very dry and not at all – icy April morning !) so having no such certain ophidians around my particular footfalls is a truly good, good thing !

    Blue

  5. Randy Schenck
    Posted April 12, 2016 at 9:41 am | Permalink

    Very interesting story and tour guide. Many people may not realize that this area is south of St. Louis. Looks more like something from Louisiana or Florida.

  6. Dominic
    Posted April 12, 2016 at 9:49 am | Permalink

    Very interesting thank Greg.

    Two questions –
    Could the tree-knees help it breathe if it needs to get air to its roots as it grows bigger?
    can snakes such as the cotton-mouth & other lunging biters – whatever the term is for that type of predation – re-grow a tooth if it snaps through misadventure?

    • Marilee Lovit
      Posted April 12, 2016 at 7:54 pm | Permalink

      Mangroves grow things like those knees also.

  7. Mark Sturtevant
    Posted April 12, 2016 at 10:11 am | Permalink

    Many years ago I had been in S. Illinois on a field trip for an entomology class, and was delighted to see a real cypress swamp, complete with buttresses, etc. I was of course looking for bugs, but I do not recall giving a thought to venomous snakes.

  8. Pliny the in Between
    Posted April 12, 2016 at 10:22 am | Permalink

    Growing up in the wooded hill country of southern Indiana, we would on occasion run across a Copperhead or a Timber Rattler. Thought to my knowledge no one ever actually encountered a true cottonmouth in that region, most people referred to any water snake with that label.

    Two of the nonvenomous water snakes in the area could cause some concerns. The common water snake of the region was a great mimic of the copperhead with similar markings and color. The much larger (and foul tempered) diamond back water snake with its thick body, diamond markings and wedge shaped head, could be mistaken for a rattler.

    The common water snakes made pretty good pets, though my mother disagreed. Surprisingly smart too. On one occasion I was catching minnows and temporarily putting them in mason jars when they started to disappear. A common water snake was hiding under the boat and would come out when I was netting for the minnows. He would sneak out, eat a fish from a jar, and bolt back under the boat.

    Common water snakes and black snakes in this region also rattled their tails in the leaves as a warning.

  9. Posted April 12, 2016 at 10:23 am | Permalink

    Very interesting post, thanks Greg!

  10. Posted April 12, 2016 at 10:49 am | Permalink

    You are a braver man than I, Greg Mayer. Those woods, replete with cottonmouth, look like something out of the Blair Witch Project.

    Thanks for the pictures. I hope you used a telescopic lens to get that close up of the cottonmouth.

  11. nickswearsky
    Posted April 12, 2016 at 11:38 am | Permalink

    Spotted it immediately. I tell ya, people really are keyed into seeing snakes. I have many, many field experiences where this has happened.

    • Posted April 12, 2016 at 1:18 pm | Permalink

      Oh yes, me too. Subconscious cognition.

  12. ToddP
    Posted April 12, 2016 at 4:22 pm | Permalink

    Great post, Greg. Nice photos/video of the snake. I have also read and enjoyed (and learned much from!) Dr. Greene’s fantastic book.

  13. Jonathan Wallace
    Posted April 12, 2016 at 5:35 pm | Permalink

    Great set of photos of what is clearly a wonderful place.

  14. gscott
    Posted April 12, 2016 at 6:50 pm | Permalink

    What a coincidence – I’ll be there myself in a couple of weeks. Among other things, I’ll ride the Tunnel Hill bike trail that starts at the Barkhausen Center. Looks like I should do a bit of hiking too, but watch where I step!

    And I didn’t know that ‘herping’ was a recognized name for snake-watching.

  15. Mark Joseph
    Posted April 12, 2016 at 10:16 pm | Permalink

    Thank you for the information, and the book on snakes is now on my to-read list.

  16. S.A. native
    Posted April 12, 2016 at 10:53 pm | Permalink

    Almost ran over a cottonmouth on my bicycle on a trail along one of the streams here in San Antonio.

    Looking down into a clear river west of here I saw a cottonmouth take a catfish in deep water and carry it out onto the gravel bank. Location is a popular warm weather swimming hole.

    They are usually easy to spot swimming because they tend to carry their large heads high out of the water.


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