When we consider snakes, we regularly image their iconic slithering, swish, wave-like movement — a organic marvel that appears to defy friction and has fascinated zoologists for many years. That’s not the one transfer these elongated, limbless creatures have mastered. They are additionally identified to climb timber, glide via the air, and navigate uneven terrain utilizing a variety of motion methods like rectilinear movement, periodic undulation, and sidewinding, amongst others.
A peculiar and beforehand unreported manoeuvre by yellow anacondas has now slithered its means into the eye of physicists — a transient, non-planar motion younger snakes undertake to transfer ahead quickly when threatened.
The place to begin of this movement has been dubbed the ‘S-start’ in a current examine led by researchers at IIT-Bombay and Harvard University, and revealed in Nature Physics.
With the assistance of a biophysical mannequin that handled the snake as an lively, elastic rod, the researchers mapped the underlying mechanical constraints and muscle torque patterns required to carry out the gait. They discovered that this type of locomotion trusted the snakes’ dimension, since solely child and juvenile anacondas exhibited it.
Raghunath Chelakkot, affiliate professor on the physics division at IIT Bombay and coauthor of the examine, stated this type of movement is primarily used as an escape response, the place snakes strive to optimise for velocity somewhat than preserve power. Unlike the everyday, well-known planar movement the place snakes transfer in a wave-like sample alongside the bottom, this newly noticed motion includes younger snakes bending their physique out and in of the airplane and partially lifting them out of the airplane.
Biophysics of transferring snakes
Despite having no arms, legs, wings or fins to propel their physique ahead or backward, snakes get round simply effective, making them a wonderful case examine in limbless locomotion. This motion doesn’t come simply, nonetheless, as a result of it requires inside and exterior buildings.
A snake’s lengthy, slender physique is constructed round a versatile backbone made up of lots of of sharply curved ribs operating its whole size. Muscles hooked up to these ribs twist and switch to push the snake ahead.
The pores and skin is roofed in versatile, keratin-based scales. On the underside, extensive stomach scales present grip whereas the smaller, extra assorted again scales assist the snake transfer easily throughout completely different surfaces with out slipping. Research has advised {that a} snake’s means to transfer, particularly on flat floor, depends closely on the directional friction created by its scales.
The inside and exterior programs allow quite a lot of distinct locomotion types: lateral undulation, the place physique waves journey aspect to aspect; rectilinear movement, which includes alternating muscular enlargement and contraction alongside the stomach; concertina locomotion, the place the physique folds like an accordion; and sidewinding, an out-of-plane gait the place snake lifts sections of its physique to kind rolling, helical curves.
But in contrast to out-of-plane sidewinding, which is a gradual movement travelling from head to tail, the newfound S-start gait is unsteady and pulsed. It begins with a burst of muscular drive that travels down the physique after which stops somewhat than persevering with to propagate.
This surprising movement prompted two compelling questions: How are they in a position to carry out this movement? And why is that this behaviour solely seen in small, juvenile anacondas and never in different species or bigger people? The solutions might have helpful functions in robotics or biomechanics, Chelakkot stated.
The physics of S-starts
To unravel the puzzle, the researchers carried out locomotor trials on 10 new child, 5 juvenile, and two grownup captive-bred yellow anacondas within the U.S. The snakes had been compelled to S-start by simulating exterior threats and high-speed video recordings tracked their motion.
The staff additionally developed a biophysical mannequin that handled the snake as an elastic rod transferring on a flat floor. This rod-like illustration of the snake captured important bodily traits — passive bending and twisting resistance, gravitational forces, and frictional interactions with the bottom — together with muscular torques (rotational forces) utilized alongside the physique.
Using the mathematical mannequin, the researchers reproduced the S-start within the presence of a localised muscular torque triplet, the place the 2 in-plane elements formed the S-curve and one out-of-plane torque on the centre contact area pushed the elastic rod towards the bottom.
The video recordings additional confirmed that to carry out the movement, the snake first varieties an S-shape composed of three straight sections related by two sharp curves. The curved components then elevate off the bottom whereas the outer straight sections slide ahead, with the center part remaining stationary. This prompted the curved areas to journey alongside the snake’s physique, propelling it ahead.
Only younger anacondas
During the locomotor trials, the researchers noticed that solely the newborns and the juveniles carried out the distinctive gait, not the adults. Numerical simulations of the snake’s motion utilizing the mannequin indicated that the S-start solely labored effectively inside a sure vary of scaled physique weight and muscular torque.
Since the gait requires the snake to elevate sure sections of the physique off the bottom whereas urgent others down, it creates a tug-of-war between muscular energy and weight.
To elevate off, the snake should overcome gravity, which turns into more and more troublesome as its weight will increase. As snakes develop, they grow to be bigger and heavier, however not stronger in the identical proportion. The bulk of the added weight comes from bone, not muscle, leaving bigger snakes with comparatively much less muscle mass per unit of physique weight. Thus, the adults lack the strength-to-weight ratio required to carry out the out-of-plane lifting essential to an S-start.
By probing the physics behind snake locomotion, the researchers discovered themselves uncovering patterns with roots in evolution. They noticed that, when utilized periodically, the torque triplets produced the well-known sidewinding movement.
“This hints at the possibility that S-start is utilised as a building block for multiple limbless gaits which involve out-of-plane bending of the body,” Chelakkot stated. “Besides sidewinding, S-start appears to be a component in ‘lasso motion’ observed in tree-climbing snakes. All these facts hint at the possible evolutionary role of S-start in non-planar limbless gaits.”
Snakes, gaits, and robots
The researchers have expressed perception that by offering exact mathematical measures to reproduce such movement in synthetic programs, these research may also help speed up innovation in comfortable robotics, mimicking limbless locomotion. One instance: snake-like robots that may navigate via very slender or confined areas.
These findings contribute to the worldwide understanding of limbless locomotion throughout all kinds of organisms, together with not simply snakes but additionally worms like earthworms and inchworms.
Chelakkot stated that finding out extremely advanced dwelling organisms with versatile motions and postures opens up prospects to increase and problem current elastic theories.
“It pushes scientists to look further into what are the different physical things that we can study to move from understanding simple bodies to more complex bodies like biological systems,” Chelakkot added.
Sanjukta Mondal is a chemist-turned-science-writer with expertise in writing fashionable science articles and scripts for STEM YouTube channels.
