Winners of the snake Olympics can inspire better robots

To the uninitiated, snakes are really just variations on a theme. Some are black, some are green. Some have pointier heads, while others have flatter snouts. Many folks think of them as little more than cylindrical tubes of death and destruction. But that’s not what University of Cincinnati biologist Bruce C. Jayne sees. Show him a Boa constrictor and a brown tree snake (Boiga irregularis) and he’ll tell you that the animals couldn’t be more different. And those differences might help engineers design better robots and aid wildlife managers in keeping invasive snakes away from places they’ll cause trouble.

Despite their overall tube-shaped form, some snakes can form angular edges along either side of their bellies. Think of the cross-section of brown tree snake not as entirely round, but as a circle on top and a square on the bottom. Jayne calls these ridges “ventrolateral keels,” because they run along the bottom and sides of the reptiles. Boa constrictor, on the other hand, really is more of a tube. It can’t form ventrolateral keels. Corn snakes (Pantherophis guttatus) are intermediate: their keels aren’t as sharply defined as those of the brown tree snakes, but they can still make them, unlike the constrictors.

To see how this ability to modify the shapes of their bodies allows snakes to more efficiently climb, Jayne gave the three species – 15 wild brown tree snakes caught on Guam, where they’re invasive; 10 corn snakes acquired from a commercial distributor; and 12 boas, born and raised in captivity at the University of Cincinnati – a sort of serpent Olympics. He took poles, covered them to duct tape to provide some texture, and added a series of pegs with different heights placed in different spots on the poles. These simulated tree branches, while the pegs simulated the bark’s roughness. What he and his colleagues wanted to know was whether the snakes had an easier time climbing trees with rougher bark (like a pine tree) or smoother bark (like an oak tree).

Increasing the height of the pegs shifted the snakes from one form of climbing behavior to another. The “rougher” poles allowed the snakes to slide smoothly up the pole without needing to use their bodies to maintain their grip on it. Instead, the pegs acted like ledges, keeping them from sliding down. The “smoother” poles required that the snakes perform more “concertina” locomotion, where one half of the snake grips the pole while the second half advances (a concertina is a type of accordion, the movement of which evokes this form of snake locomotion).

Thanks to their ventrolateral keels, the brown tree snakes were the most efficient climbers, even when faced with smooth, near-vertical surfaces. The boa constrictors were least efficient when it came to the more difficult challenges, while the corn snakes were right in the middle. The boas almost always had to use the more energy-intensive concertina behavior: they’re just not built for climbing trees.

This isn’t purely an academic exercise. A collapsed building may not be accessible to humans or wheeled robots as rescuers assess the situation and look for survivors. A snake-inspired robot, however, just might be able to traverse the rubble – but only if it can move about efficiently.

And in places where snakes are invasive, a better understanding of how they climb can aid wildlife managers. For example, brown tree snakes have a habit of climbing power poles and short-circuiting the lines on Guam. If engineers can figure out how to make those poles “un-climbable,” then residents won’t have to contend with snake-involved power outages. Since we now know that brown tree snakes can climb with the aid of pegs just one millimeter high, such interventions will require incredibly smooth surfaces.

Meanwhile, a similar solution can allow wildlife managers to prevent the reptilian invaders from climbing trees in search of endangered or threatened birds and nestlings to eat. – Jason G. Goldman | 30 December 2015

Source: Jayne, B. C., Newman, S. J., Zentkovich, M. M., & Berns, H. M. (2015). Why arboreal snakes should not be cylindrical: body shape, incline and surface roughness have interactive effects on locomotion. Journal of Experimental Biology, 218(24), 3978-3986. DOI: 10.1242/jeb.129379.

Header image: Brown tree snake via USFWS/Wikimedia Commons (Public domain).

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