Biomechanics of Sand Swimming

Jonathan Webb of the BBC reports on fascinating work at Professor Daniel Goldman’s lab at Georgia Tech http://crablab.gatech.edu/, investigating how snakes “swim” through sand (a “frictional fluid”). This locomotion is more than a little amazing, and we’d like to understand how the snake’s body and movement achieves such magic. As one of their papers indicates, this question is interesting for understanding of evolution and for the development of biomimetic robots. [1], p. 440

The BBC report describes a variety of experiments with the surprisingly photogenic shovel-nosed snake (Chionactis occipitalis), using sand tables, a variety of cameras and imaging, and computer simulations to measure and understand the behavior of the animals.

Looking at a recent paper, it is really cool to see how this science develops [1]. This particular study compared the shovel-nose snake to sandfish lizard (Scincus scincus), which also swims through sand. One notable difference is that the snake is, well, “snakey”, long and skinny. The sandfish is, well, more “lizardy”, not as elongated. These differences are quantified in Table 2 (p. 442) (Table 2 is perhaps unconsciously funny, reporting that snakes are different from lizards with “p < .01” on these measures.)

Grokking the sand swimming is actually quite complicated. Shovel-noses and sandfish swim differently, and much depends on how sand actually works. The paper explains how they analyzed the swimming motion and the sand.

They conclude that “the longer body and lower friction allows the snake to achieve a higher undulation efficiency and lower mechanical CoT than possible for a sandfish” (p. 446) They speculate that “the bauplan exemplified by the shovel- nosed snake may also approach that of an optimal sand swimmer.” (p. 446)

The lizard and the snake evolved independently, but have developed similar behaviors and adaptations. “Our comparisons reveal evident patterns of performance optimization and constraint based on two remarkably different squamate body forms.” (p. 448)

These detailed biomechanical studies provide models that can be used for developing biomimetic robots. For that matter, biomimetic robots offer a form of experimental test of theoretical models, allowing examination of “designs” not seen in nature.

Cool stuff.


 

  1. Sarah S. Sharpe, Stephan A. Koehler, Robyn M. Kuckuk, Miguel Serrano, Patricio A. Vela, Joseph Mendelson, and Daniel I. Goldman, Locomotor benefits of being a slender and slick sand swimmer. Journal of Experimental Biology, 218 (3):440-450, 2015. http://jeb.biologists.org/content/218/3/440.abstract

 

Robot Wednesday

 

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