- The skin of the Calabar burrowing python is 15 times thicker and orders of magnitude harder to pierce than the average snake. The skin’s puncture resistance is owed to its layered sheets of collagen fibers.
- Scientists think the snake’s tough skin may have evolved to protect the snake from the bites of mother rodents defending their young, which make up the entirety of the Calabar’s diet.
- The snake’s skin is flexible despite being thick and nearly impenetrable. This unique combination of qualities has already intrigued a pharmaceutical company hoping to mimic its structure to create puncture-resistant medical gloves that don’t restrict movement.
The fury of rodent mothers may have given rise to the toughest of all snakes.
The skin of the Calabar burrowing python (Calabaria reinhardtii), a one-meter-long snake native to equatorial Africa, may be thicker and harder to pierce than any other snake in the world, according to a study due to be published in the January issue of the Journal of Morphology. The Calabar’s armor-like casing may have evolved to ward off biting attacks by the protective mothers of its exclusive prey: the pups of burrowing rodents.
Snake skin, like human skin, has an outer epidermis and a deep dermis. In snakes, scales compose the outer layer. Typically, the deeper layer in both snakes and mammals is made up of disorganized bundles of collagen, arranged like loose piles of hay. This lack of structure makes skin quite elastic, but it’s also easily punctured or sliced.
The Calabar python’s skin is remarkably different. The discovery arose from a bit of grisly serendipity, recalls study co-author Bruce Young, a biophysicist at A.T. Still University in the U.S. state of Missouri.
In 2015, Young and his colleagues were comparing the brain structures of different snakes. Their project required decapitating quite a few of them.
“We had gotten this down to a science, but when we got to the Calabar we couldn’t do it,” Young told Mongabay. The razor blade that had easily sliced through every other snake met its match in the Calabar’s tough sheath of skin. A brand-new surgical scalpel and an extra helping of brute force finally separated the Calabar’s head from its body.
Intrigued by the struggle, Young kept a bit of the snake’s skin to investigate what had rebuffed his blade. It was thicker than anything Young had come across, so the team took a close look at its structure.
A research team led by Dawei Han of Truman State University, also in Missouri, pitted the Calabar’s skin against that of 13 other species of snake. They assessed its thickness with a microscope and its puncture resistance with hypodermic needles and a force transducer, which measured the pressure required to poke through the skin. Results showed that the Calabar’s skin was 15 times thicker and orders of magnitude harder to pierce than the skin of any other snake in the study.
Under magnification, color-stained cross-sections of the skin revealed highly organized layers of collagen under the snake’s scales. Bundles of collagen in each layer ran perpendicularly to those above and below — a tough crisscross arrangement more similar to the hide of a rhinoceros than to the skin of other snakes.
The work has surprised and delighted other herpetologists. “Most snakeskin has collagen fibers that run parallel. That organization allows the skin to stretch around a large meal or eggs,” says morphologist Alan Savitzky of Utah State University in the U.S. Savitzky has studied snakes for 35 years but was not involved in the present study. “These cross-ply fibers in the Calabar dramatically increase its strength but reduce its ability to stretch. It’s a very significant finding.”
Despite its toughness, the snake’s skin remains flexible. This combination of pliability and puncture resistance has already piqued the interest of a pharmaceutical company seeking to make tougher medical gloves that don’t restrict movement. The company reached out to Han and Young for guidance in mimicking the underlying structure of the Calabar’s skin, according to the researchers.
Several other aspects of the snake’s physiology have captured the attention of serpent aficionados. For instance, it looks like a “snake with two butts,” as described by Bruce Young’s 10-year-old daughter, because its head and tail look almost identical. Both ends of the Calabar are blunt and oblong — the head a bit thinner and the tail a bit thicker than the average snake’s. The snake presents its tail — shielded by the thickest skin on its body — to would-be assailants while burying its head beneath its coils.
The Calabar’s armor creates some limitations. Calabar pythons have one of the smallest clutch sizes of any snake, for instance. Females lay only four eggs on average, whereas more elastic snakes can lay up to 100. The eggs themselves are long and slender, rather than the chicken-like eggs produced by many other snakes.
And while most snakes can famously eat things far bigger than their own heads, the Calabar’s thick skin limits its ability to swell. This partly explains their preference for eating infant rodents. Despite being a close relative to constrictors, which subdue their prey by coiling around it and squeezing, the Calabar’s technique might more accurately be described as “squashing.” Within the tight quarters of underground burrows, the snakes squish their tiny prey against the earthen walls. This tactic allows the Calabar to kill and eat entire litters at once.
The individual scales of the Calabar burrowing python, which modern genetic analysis reveals is actually in the boa family despite “python” being in its common name, are only a bit thicker than those of most snakes. However, they’re packed more closely together.
“With most snakes you can spread their scales apart and see the inner skin between the scales,” said Young. “You can’t spread the scales of the Calabar.” Pressing down on the scales also appears to make them lock together even more tightly — something Young is anxious to study.
“No other snake approached the skin condition of the Calabar,” said Young. “This really is a novelty among snakes.”
CITATION
- Han D, Young BA. The rhinoceros among Serpents: Comparative anatomy and experimental biophysics of Calabar burrowing python (Calabaria reinhardtii) skin. Journal of Morphology. 2018; 279:86–96. doi:10.1002/jmor.20756
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