Image of a green tree python from www.kids.britannica.comJ.H. Pete Carmichael—The Image Bank/Getty Images
Dr. Greg Byrnes (Siena College, Loudonville, NY) and Dr. Bruce Jayne (University of Cincinnati, OH) discovered that snakes use more force than is necessary to support their weight when climbing. To climb, snakes rely on friction and repeatedly contract and extend their bodies, a process called concertina locomotion. To study the forces generated by snakes during this type of locomotion, the researchers constructed a vertical cylinder that was covered with textured tennis racket tape (for friction) and pressure sensors. They also calculated the minimum gripping force (i.e. coefficient of friction between the snake and the surface) exerted by the snakes to avoid falling off by putting the snakes on a flat surface covered with the textured tape and slowly tilting the board until the snake began to slip.
What they found was a range of responses in which some snakes used minimum force to climb the vertical tube whereas others used almost 20 times the force needed to prevent slipping. Study author Byrnes was quoted in LiveScience saying, "The vast majority of time, the safety factor was between 2.5 and 5. They are using a force that's not at their maximum, but not at their minimum, either." Perhaps they are gripping tightly to avoid falling off and having to climb back up or perhaps a tight grip is important to avoid predators or to attack prey. Whatever the reason, the study authors mentioned that the excess gripping force does not likely cost the animals too much overall in terms of energy expenditure.
Similar to snakes, the authors report that humans typically grip objects at 2-4 times the amount of force required to support their weight. Personally, I think I am closer to 4 times.
Sources:
Byrnes G, Jayne BC. Gripping during climbing of arboreal snakes may be safe but not economical. Biology Letters. 10(8): 20140434, 2014.
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One night I watched a corn snake climb a vertical 2" square aluminum pole. Sounds easy, just wrap around it and squeeze as you climb. But this snake didn't wrap around the pole. It adopted an S-shape across a flat and hung a bit of body over the edge to give it a gripping surface. By essentially forming a series of biological C-clamps as grips it advanced rapidly up the smooth pole.