Elephant Whiskers: The Secret to Their Trunk's Sensitivity and Strength

Pachyderm whiskers are more flexible at the tip than the base, allowing elephants to complete delicate tasks with their incredibly strong trunks. Watching an elephant forage for roots to eat reveals just how strong yet sensitive its trunk is. An elephant’s more than 40,000 trunk muscles can upend trees and follow it up with gently collecting the fragments that fell. It takes baby elephants nearly a year to master using their trunks in this way, and it’s taken humans even longer to understand how they’re able to do it. The secret may come down to elephants’ whiskers.

Now researchers who analyzed the whiskers lining these animals’ trunks have discovered a unique structural property that helps elephants sense the world around them and determine whether a task calls for strength or sensitivity. In a study published today in Science, researchers reveal that—unlike the whiskers of other mammals—those of elephants are more flexible at the tip and stiffer closer to the skin. This observation clarifies how the unique structure of the animals’ whiskers informs elephants’ “umwelt,” or their individual sensory and perceptual experience of the world.

“We found elephants are like aliens,” says Andrew Schulz, lead study author and haptic intelligence researcher at the Max Planck Institute for Intelligence Systems. “They have these hornlike whiskers with a stiffness gradient ... that was puzzling.” Because elephants have such rough, armorlike skin, researchers knew the whiskers on their trunks were likely doing a lot of sensory work to allow the animals to interact delicately with the world around them. But to truly understand these tiny filaments, researchers needed a much closer look.

Using a CT scanner specially built for small objects, Schulz and his colleagues created a digital rendering of the elephant whiskers to analyze their structure from the inside out. Then, using other imaging and chemical tests, they were able to further analyze the whiskers’ structure and hardness. The part of the whisker closer to an elephant’s skin is very strong and porous. The tip of the whisker, meanwhile, is much more flexible and denser.

Wanting to understand the mechanics of this unique form, the researchers 3D-printed a supersized version of a whisker with an accurate density gradient to feel for themselves. “I was walking down the hallway and hitting things [with the whisker] and I had this true eureka moment,” says Katherine J. Kuchenbecker, senior author of the study and director of the haptic intelligence department at the Max Planck Institute for Intelligence Systems. She noticed that hitting something hard with the dense base of the whisker felt much more solid and crisp than hitting something with the duller end. The difference in hardness allowed Kuchenbecker to get a sense of objects’ contours without her skin even touching them.

Elephants use their trunks to breathe, smell, grab things, communicate and even perceive objects outside their line of sight. And their whiskers help shape all of these experiences. “Nearly every mammal—not just elephants—has whiskers whose size, shape and material properties are almost certainly adapted to the way that species uses touch in its environment,” explains Mitra Hartmann, an engineering professor at Northwestern University, who was not involved in the study.

In addition to providing a glimpse into the perceptual world of elephants, Schulz and his team have made a tool kit with their data available in the hope that the unique structure of elephant whiskers will inspire researchers in other disciplines. They are particularly interested in seeing how materials with a stiffness gradient—like an elephant whisker—could be applied to robotics. Maintaining machines’ strength while being soft enough not to damage the materials they interact with is a major challenge of robotics.

“This study is a fabulous example of interdisciplinary science,” says John Hutchinson, an evolutionary biomechanics professor at the University of London’s Royal Veterinary College. “It is elegant neuroscience, anatomy and mechanics.”