Snake on a wire

[JAC: In lieu of “readers’ wildlife” today, we have “Mayer’s wildlife”: His disquisition on snake locomotion. Be sure to keep those photos coming in, and don’t worry if you haven’t seen yours yet, as I have them all.]

by Greg Mayer

Matthew sends the following tweet of a tiger snake making its way along a wire fence.

At first glance, two things struck me at about this, aside from its generalized coolness. The form of locomotion is a typical one for snakes called lateral undulation, in which waves of muscular contraction alternate down the sides of the body. You can see the snake is pushing first on one side of the wire, then the other, in waves down the body. This is not unusual for snakes. And there are many arboreal snakes (vine snakes, parrot snakes, etc.) that habitually move along very narrow surfaces, such as vines and branches. The novelty here to me is the length of the narrow surface– most vine snakes frequently encounter crosswise vines and branches, so they don’t move for any great distance in a perfectly straight line along a narrow surface, as this snake is doing.

But its movements are not unprecedented. While checking into this particular mode of locomotion, I found the following in Carl Gans’ Biomechanics: An Approach to Vertebrate Biology (p. 93):

Other climbers show a fabulous ability to throw their trunk into multiple, regular, and controlled bends of very short radius. The African file snakes (Mehelya) apparently can travel along telephone wires with alternate half-loops hanging respectively over the left and right sides of the wire.

The second thing that struck me was that a tiger snake is not a vine snake of any sort– they’re terrestrial. So, climbing along wires is not where I would expect to see them. But that’s book knowledge, and perhaps Australian readers can enlighten us from experience.

On reflection, I was also struck by this being an example of what Gans called “excessive construction”– the ability of structures (and in this case also behaviors) to be successfully used in circumstances that were not part of the historical evolutionary development of the structure. Gans thought, and I agree, that such circumstances can be the basis for adaptation (i.e. heritable changes in the structure/behavior) to the new circumstances.  Again from Biomechanics (p. 14-15):

Gans provides a much more insightful view here of how functions change, and how new adaptations arise, than did Gould and Vrba in their largely unnecessary coining of the word and concept “exaptation“.


Gans, C. 1974 (1980). Biomechanics: An Approach to Vertebrate Biology. University of Michigan Press, Ann Arbor.

Gans, C.  1979.  Momentarily excessive construction as the basis for protoadaptation.  Evolution 33:227-233.

Gould, S.J. and E.S. Vrba. 1982. Exaptation- a missing term in the science of form. Paleobiology 8:4-15. pdf

45 Comments

  1. Michael Day
    Posted February 16, 2018 at 7:51 am | Permalink

    That would be a good place for a tiger snake to catch a “bird on a wire”.

  2. Ken Kukec
    Posted February 16, 2018 at 8:10 am | Permalink

    Bet there’ve been some Glenn Campbell-style linemen out in Witchita who’ve been given the fright of their lives by this sort of thing.

  3. Gamall
    Posted February 16, 2018 at 8:15 am | Permalink

    That snake’s coolness level is well over 9000.

    “excessive construction” is how I’d imagine the brain came about, from a computer science pov.

    Not hard to get a useful structure that acts like a finite state automaton. Add a little memory, and suddenly you have Turing completeness (a huge leap: there is nothing above that in computational power*). Whatever specialised use drove its apparition, the machine can then be hijacked and re-purposed in endless ways.

    * I’ll shoot anyone who says “quantum comp… BANG! ARHG!”, because it’s easier than to explain why it’s a bad answer 😛

    • Gamall
      Posted February 16, 2018 at 8:17 am | Permalink

      Hum, I’m positive I had a warning tag “excessive simplifications follow”, but I wrote them XML-style and they were eaten by WordPress.

      Well. Excessive simplifications precede, then.

  4. davidintoronto
    Posted February 16, 2018 at 8:17 am | Permalink

    Thank you for this post, Dr. Mayer.

  5. Michael Fisher
    Posted February 16, 2018 at 8:25 am | Permalink

    The snake ‘knows’ to keep its CoG below the wire until time 0.19 when its head end reaches up too far to mount that post.

    • rickflick
      Posted February 16, 2018 at 12:34 pm | Permalink

      At one point his head spun around almost upside down which suggests his sense of balance, whatever the mechanism is, works well to compensate for the extreme rotation. I’m not sure human balance would be as flexible.
      Now I’ve made myself curious about snake balance and orientation. Do they have semicircular canals?

  6. Randall Schenck
    Posted February 16, 2018 at 8:27 am | Permalink

    The tiger snake has perfect balance. During my years in Okinawa they had the snake shows for the tourists. Part of the show was to compare a cobra snake to their local snake, the Habu. It was much easier to hand the cobra because it could only strike in one direction. You could walk around back of it and actually tap it on the head. The Habu could strike in any direction 360 degrees and was impossible to get close to.

    • Diane G.
      Posted February 16, 2018 at 11:24 am | Permalink

      How interesting!

    • Posted February 16, 2018 at 3:59 pm | Permalink

      Hmmn. Not very good at snake identification. Figure I will just not try and tap any snake on the back of the head.

  7. Posted February 16, 2018 at 9:21 am | Permalink

    I like it! I had been using the term ‘exaptation’ for years as a handle on this sort of thing, & that term has been used a lot, but I like the descriptions here & the terms ‘excessive construction’ and to ‘proto-adaptation’. They came first, and also they pretty clearly say what they are about.

    • Diane G.
      Posted February 16, 2018 at 11:36 am | Permalink

      The term “preadaptation” was in use even earlier, IIANM (a brief search suggests the first use was in 1958) before it was kicked out for (supposedly) being too teleological. One of the first examples of political correctness? Possibly before PC was even a term…

      Personally I think it comes far closer to defining the concept than “excessive construction” or the artificial “exaptation,” but that’s just me…

      (Cue lectures about why it’s important to not use words regarding evolution that could be interpreted as teleological…)

      • Posted February 16, 2018 at 1:15 pm | Permalink

        “Preadaptation” goes much further back than 1958. Gans introduced “protoadaptation” explicitly to replace preadaptation because of its possible teleological connotations. By the 1950s, preadaptation had been shorn of its teleological and mutationist origins, and I prefer the term myself. Gans’ excessive construction is, however, a useful addition to our concepts, since it specifies how the inexactness of the structural fit to the current environment, combined with behavioral flexibility, can lead to selection for the intensification of or change in the function of a structure, and thus adaptation to other features of the organism’s conditions of existence.

        GCM

        • Diane G.
          Posted February 16, 2018 at 1:47 pm | Permalink

          Thanks, Greg! I can see how it is a useful addition.

          (FWIW, I had been under the impression that the anti-preadaptation campaign had, if not begun with, at least re-arose with Stephen J. Gould [surprise, surprise] in, I think, the 70’s or a bit later…but I certainly can’t say I followed the discussion at all closely.)

  8. Posted February 16, 2018 at 9:36 am | Permalink

    I am obviously not familiar with the antics of this species of snake, but it appears that this snake finds moving along the wire a challenge. It is struggling to maintain balance and moving slowly forward. If so, what would motivate it to do this? I would suspect that it also makes it more vulnerable to its predators as it can easily be seen. On the other hand, perhaps its predators are on the ground and even less skilled at climbing.

    • Diane G.
      Posted February 16, 2018 at 11:41 am | Permalink

      Yes, that was the first thing that occurred to me, too! Obviously it’s not gonna sneak up on any wire-sitting prey like that, and as you say, it’s far more vulnerable to raptors and any other predators.

    • nicky
      Posted February 16, 2018 at 11:57 am | Permalink

      Yes, that struck me too, how difficult it appeared for this snake to keep it’s balance.
      What motivated that snake to mount a wire? Strange. Luckily it was not razor wire (a SA’n invention) or electrified.

    • Heather Hastie
      Posted February 16, 2018 at 5:32 pm | Permalink

      Also what I thought. Why would the snake do this? Surely it would be easier and quicker to slither along the ground? And the snake would be better camouflaged on the ground too. Perhaps the wire is cooler?

      • Posted February 16, 2018 at 5:47 pm | Permalink

        I know! The scientist placed the snake on the wire just to see what it would do!

  9. DTaylor
    Posted February 16, 2018 at 9:46 am | Permalink

    Very interesting post. Thanks.

  10. busterggi
    Posted February 16, 2018 at 10:20 am | Permalink

    Damn but this will make my cats jealous!

    Garter snakes are generally terrestrial but I’ve seen them up in low bushes as well.

  11. Posted February 16, 2018 at 11:44 am | Permalink

    I wonder what neural mechanisms prompt the snake to “think” it can do this and hence try it out.

  12. Posted February 16, 2018 at 12:27 pm | Permalink

    “A new biologic role (engendered by a new behavior) seems to precede a “new structure””

    So no hopeful monsters then, eh? Too bad.

  13. Posted February 16, 2018 at 2:56 pm | Permalink

    Jerry is correct in asserting that this behaviour is very unusual for a Tiger Snake. They certainly are completely terrestrial, and more than that, you generally don’t find them in the vicinity of trees; they tend to inhabit the grassy scrub near rivers and marshes. It’s unclear what the snake in question was doing, but the way it was “tasting” the wire with its tongue suggests that it may have been following the trail of a potential prey.

    Although I’ve never seen a Tiger Snake climb a wire fence before, I’d guess that any snake with rectilinear locomotion would be able to do so (in particular, I suspect that all Australian elapids are able to do this). Finally, let me say that the Tiger Snake is one of the most venomous snakes in the world, whose bite delivers a very potent neurotoxin. Moreover, the snake in the video is a *big* Tiger (you can see the swollen venom glands on the side of its head). Anyone who encounters that snake would be well advised to behave with caution.

    • Posted February 16, 2018 at 2:58 pm | Permalink

      Note that I didn’t write this; it’s stated in bold at the top that this is Greg’s post.

      jac

    • Posted February 16, 2018 at 3:06 pm | Permalink

      Ah, the best motivation in the world … dinner!

  14. Posted February 16, 2018 at 3:04 pm | Permalink

    A question to any readers from Oz: Why is it called a Tiger Snake? Its aggressiveness?

    We were always told the the Tiger Snakes were the ones to really watch out for!

    • Posted February 16, 2018 at 3:24 pm | Permalink

      Not from Oz, but, though frequently melanic, they have stripes.

      GCM

    • Frank
      Posted February 16, 2018 at 8:25 pm | Permalink

      They do have a reputation for being aggressive but, as Barbara mentions below, it’s because they have stripes (at least the mainland varieties do) that they have the “Tiger” moniker.
      And they most definitely have right of way when encountered in the wild!

  15. Barbara Radcliff
    Posted February 16, 2018 at 5:04 pm | Permalink

    I’ve only seen a few tiger snakes (and kept my distance), but I believe that mainland tigers have obvious stripes while those from islands such as Tasmania and Kangaroo Island (among others tend to be black).

  16. gravelinspector-Aidan
    Posted February 16, 2018 at 5:04 pm | Permalink

    most vine snakes frequently encounter crosswise vines and branches, so they don’t move for any great distance in a perfectly straight line along a narrow surface

    On second glance at the still (video not playing at this end), the fence has vertical strands at about twice the vertical spacing of the strands. Where they meet, there are several turns of wire around the top strand. That’s sufficiently similar to a branch’s side-branches to bring it a lot closer to the natural situation. I can’t see the video to see how it affects the vertical and horizontal motion of the wire, but I bet they’re damped, a lot.

    • infiniteimprobabilit
      Posted February 21, 2018 at 3:36 am | Permalink

      I noticed that – the lower horizontal wires are connected by vertical wires, which the snake could use to rest against and stabilise its balance, but the top wire does not. So in the last bit of the video, the snake is proceeding unstabilised along the top wire. Too bad the video stops before the snake will have got far enough that its back end has left the stabilising support of the vertical post, so we can’t tell what will happen.

      cr

  17. hugh7
    Posted February 16, 2018 at 6:34 pm | Permalink

    What struck me is that spiralling around the wire does not seem to be in its repertoire. (I want to see the full length, to see what the tail end does.) Spiralling would remove the balance issue and enable it to move much faster. I guess it doesn’t spiral because spiralling has no ground-level equivalent: it just adapts its terrestrial movement to a very narrow piece of “land” – and as is evident when it goes upside down, one that it grasps around its cylindrical surface. So the algorithm is very simple indeed: 1. Keep touching the surface. 2. Send transverse waves down your body. Spiralling would require a whole new paradigm.

    • Michael Fisher
      Posted February 16, 2018 at 7:04 pm | Permalink

      At no time is this snake in a spiral configuration – if you were brave enough you could lift the snake up off the wire without the snake having to unwind from around the wire. What’s really happening is the snake forms a series of half loops of its body that dangle below the wire on alternate sides of the wire – like a series of snakeskin saddles.

      From the head that’s a quarter turn around the wire clockwise [CW] then a reverse half turn anti-CW, making the 1st half loop & a bit, then a half turn CW, making the 2nd loop & a bit on the opposite side – and so on. The ‘spiral’ reverses every 180 degrees.

  18. Posted February 16, 2018 at 7:45 pm | Permalink

    Science post!

    • Mark Joseph
      Posted February 17, 2018 at 9:17 am | Permalink

      Yes, I just wanted to say that I read the science post too.

      Fascinating. Great video, great discussion.

  19. Frank
    Posted February 16, 2018 at 8:27 pm | Permalink

    Good stuff – as was the related article criticising exaptation. The more I read about Steve Gould the more I get the impression he got as much wrong (maybe even more) than he got right about evolution.
    Would that be a fair assessment?

  20. ThyroidPlanet
    Posted February 17, 2018 at 1:53 pm | Permalink

    Isn’t it possible for the snake to maintain one part of its body on one side of the wire while still undulating and producing forward motion?

    Such that it would no longer appear to alternate from one side to the other?

    Or would that mean there would be no forward motion?

    • Michael Fisher
      Posted February 17, 2018 at 2:24 pm | Permalink

      Isn’t it possible for the snake to maintain one part of its body on one side of the wire while still undulating and producing forward motion?

      Are you asking if most of the body could be to the right [for example] of the wire with very little to the left?

      If that’s your question then I would say “no, the snake would fall off the wire”. If you watch the video for one second starting at 0.12… the snake briefly wobbles on the wire because the centre of gravity of the front half of the snake is rising to the height of the wire & the front half suddenly swivels around the wire under gravity. Unfortunately we can’t see all the snake, but the tail end must have applied a countervailing torque by virtue of the mass of its dangling loops to restore order.

      In other words. On something as thin as a horizontal wire the snake can’t have much muscular grip & it’s liable to swivel around the wire under its weight & fall off. It prevents this by hanging loops to both sides of the wire to act as pendulums. The CoG MUST be below the wire for stability.

      • ThyroidPlanet
        Posted February 17, 2018 at 3:00 pm | Permalink

        Yes, and your explanation makes sense

        I was wondering if the snake – or another one – has a handedness. It undulates and appears to go from one side to the other…

        The more I think about it, i think my scheme would mean an immobile snake.

        I wonder if it can go backwards on a wire.

        • Michael Fisher
          Posted February 17, 2018 at 3:26 pm | Permalink

          I’m not a snakeologist so I’m prepared to be shot down, but at the best of times land snakes never [or very rarely] go backwards. It would have to reverse the direction of its body ripples which are probably mostly [or entirely?] hard wired mentally to work in one direction.


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