If I were to pick one modification to make to my own human form, I would choose to swap my nose for an elephant's trunk. The trunk really is an anatomical Swiss Army penknife: one appendage, many functions. Elephants use their trunks to grab heavy objects, deftly manipulate light items, feed themselves, shower and even breathe underwater. Some of these behaviours share an elusive quality that is hard to observe unless you try really hard to look for it – suction force.
David Hu, Andrew Schultz and Jia Ning Wu from the Georgia Institute of Technology (Georgia Tech), USA, wanted to find out how elephants use suction to manipulate the world around them. Along with their colleagues – both human and proboscidean – from Georgia Tech, the University of Alabama, the Icahn School of Medicine at Mount Sinai and Zoo Atlanta, USA, they devised experiments to showcase how elephants use their trunks to lift material off the ground and store it in their trunk.
The trio, accompanied by Sung Yeon Sara Ha, Greena Kim (also from Georgia Tech) and Stephanie Braccini Slade from the University of Alabama, worked with the elephant keepers at Zoo Atlanta and an adult female African elephant, weighing in at 3360 kg. The scientists gave the elephant a series of foodstuffs to pick up with her trunk, varying the size, number and type of food items. They wanted to find out whether the elephant would use suction to draw the foodstuff to her trunk, or whether she would simply pick it up with the top of her proboscis.
First, the team tried to tempt the elephant with cubes of swede cut into different sizes. Regardless of size, the elephant preferred to suction the food into the tip of her trunk whenever there were 10 or more pieces. Fewer than 10, and she was content with picking up each cube individually. Suction feeding seems to be a convenient way of gathering lots of small objects at once. Next, the researchers tried out the elephant's tactile proboscis on large, fragile, tortilla chips. This time the elephant carefully used suction to levitate the crispy snack off the ground, before transporting it to her mouth – without even breaking it. Schultz, Wu and Hu were delighted to see how the trunk, a thick muscular tube weighing 100 kg alone, could be used in such a precise manner.
Elephants also use their trunk to suck up, store and transport water, sometimes to drink, and other times to shower themselves with. How much water can an elephant's trunk hold? The team and Sam Rivera from Zoo Atlanta measured the volume of water that the elephant preferred to suction into her trunk, while using an ultrasound probe to show how the muscles of the trunk worked to accommodate the water.
The ultrasound images revealed that the muscles, radiating from the centre to the edges of the trunk, are capable of dilating the volume of the nasal passages by, in some cases, up to 64%. Using this extra reservoir, the elephant was able to accommodate and rapidly expel 5.5 l of water at a time. The trunk isn't just a static drinking straw; instead, it's a distensible organ under fine muscular control. By combining their experiments with mathematical modelling, Schultz, Wu and Hu found that the trunk is capable of shifting air at a speed of 150 m s−1 – on a par with bullet trains in Japan.
How does this compare with our ability to suction food from the floor? A person can just about lift a piece of paper from the ground using suction, but next to an elephant it would be a far less dignified manoeuvre. Rather than teaching human beings new tricks, Hu and colleagues hope that the elephant's trunk will inspire a new generation of robots based on their extraordinary capacity to manipulate objects by hoover power.