How do elephants eat cereal? With a pinch | Science News for Students

How do elephants eat cereal? With a pinch

Learning how elephant trunks pick up snacks could help engineers design flexible robots
Dec 7, 2018 — 6:45 am EST
an photo of an elephant holding its trunk to its mouth to eat some food

With their long, flexible noses, elephants can eat whole tree branches like they were stems of broccoli. But they use a newfound tactic to pick up tiny bits of food, scientists have just shown.  


Never challenge an elephant to an eating contest. A fully-grown elephant can down 200 kilograms (that’s 440 pounds) of greenery every day. It can snap off whole tree branches and munch on them like giant stalks of broccoli. But how do elephants keep up their eating pace when faced with smaller food pieces , such as a bowl of cereal? They simply press and pinch with their flexible trunks, a study now finds. This newfound tactic could guide engineers in designing better flexible robots.

David Hu usually focuses on the other end of an elephant. He is a mechanical engineer — someone who studies how things move. He works at the Georgia Institute of Technology in Atlanta. Hu and his colleagues had spent a lot of time at the Atlanta zoo taking videos of elephants from behind. Specifically, he notes, they studied “elephant peeing and pooping.” His lab had been comparing how quickly different animals get rid of their wastes.

But the other end of the elephant is interesting, too, pointed out a curator at the zoo. When Hu finally got a demonstration, he was impressed. “I’d never seen them eat anything,” he says. “When there’s lots to gather they’re very fast — I would almost say greedy.”

an animated gif showing how Kelly the elephant uses her trunk to grab bran cereal
This is Kelly eating bran cereal. Note how she presses and pinches her trunk back. 
Wu et al. 2018

Hu’s team began to wonder how elephants used their trunks to gather different types of food. They were especially interested in how these animals picked up granular materials — things such as cereal, flour or sugar. “Granular material is anything made up of lots of smaller pieces,” explains Scott Franklin. He’s a physicist at the Rochester Institute of Technology in New York.

“Granular materials are between solids and liquids,” notes Karen Daniels. She’s a physicist at North Carolina State University in Raleigh and did not take part in the new study. Such materials behave unpredictably, she says. For example, when someone tries to pour cereal out of a box, it may get stuck. Bang on the box and a cereal avalanche suddenly overflows the bowl. Studying how other animals — such as elephants — lift weird materials might help engineers develop robots that can do the same thing.

Press and pinch

Hu, Franklin and their colleagues took video of Kelly, an African elephant at the Atlanta zoo. They filmed her eating rutabagas that had been chopped into large, medium and small cubes. They also tested Kelly on tiny grains of toasted bran cereal. You might think of these as the elephant equivalent of Wheaties. “Cheerios would be too expensive,” Hu explains. “She eats a lot. A box of Cheerios would only take about two minutes.”

Researchers placed Kelly's snacks on a device called a force plate. It measures how much force the elephant used to grab the food atop that plate. Kelly got 24 sets of snacks. She reached out and curled her trunk around some rutabaga pieces. Then she scooped them from the side. This is a bit like grabbing a pile of things in the crook of your elbow, Hu explains.

an animated gif showing how Kelly the elephant uses her trunk to grab veggie chunks
This is Kelly eating veggie chunks.
Wu et al. 2018

The scoop didn’t require much force — only about six newtons. That’s about 10 times the force needed to press a computer key. Kelly used the same trunk-curling motion to pick up bigger veggie chunks. But she took a different tack with the small bits. Now Kelly stretched her trunk out and pressed down on the pile of food. Then she pinched the ends of her nose together to pick it up. As she pinched, the trunk's tip formed a joint — an impressive feat for this long, boneless nose.

This push-and-pinch method took more work. When the cubes were large, it took about 10 newtons of force. For the cereal, it took about 40 newtons.  That’s delicate work for a big trunk — using only about one-twentieth as much force, on average, as it takes for a human to bite something.

“When you pick up piles of particles, you’re using friction,” explains Franklin. That’s the resistance between objects rubbing against each other. With enough friction, particles stop moving. Instead of pouring like a cereal or sliding around like a pile of rutabaga chunks, the particles start acting more like one solid piece.

The more particles the elephant lifted, the more force she had to use. With only a few rutabaga chunks, there are fewer spots for friction. So Kelly didn’t need to press as hard. But with cereal, there are many friction spots — places for a grain to slip free. So the elephant applied a lot more pressure. Hu, Franklin and their colleagues published their findings October 24 in Journal of the Royal Society Interface.

a series of composite images showing how Kelly the elephant picks up different snacks with her trunk
Press and pinch! These images show Kelly picking up snacks of different sizes. For each one, she presses down with her trunk to jam the pieces together, then pinches and scoops to pick them up.

A nose for inspiration

“I’m always jealous when I read [Hu’s] papers,” says Daniels at NC State. “He got to go to a zoo and do experiments with animals,” she explains. “I only do experiments in the lab.”

Elephants might be fun, but they also can be hard to work with. For instance, an elephant might decide, one day, not to cooperate. Still, Daniels thinks working with them is worth the effort. “It’s a way for us to get creatively inspired.” People trying to pick up a pile of cereal might think of a broom and a dustpan. An elephant doesn’t have that option. When you bring such a challenge to another animal, as here, “It gives you more and different ideas,” she points out.

The new findings aren’t limited to elephants anxious to scarf up snacks. The limbs on robots also might jam particles together to pick them up, says Daniel Goldman. He studies biophysics — the physical forces exerted by living things — at Georgia Tech in Atlanta. He was not involved in the study. “Soft robotic devices would be a natural for such things,” he says. Engineers could create flexible robots that can pick up small particles by jamming them together elephant-style. That might help robots take on all of life’s challenges — including picking up crumb-like bits.

Power Words

(for more about Power Words, click here)

biophysics     The study of physical forces as they relate to living things. People who work in this field are known as biophysicists.

colleague     Someone who works with another; a co-worker or team member.

curator     Someone who manages a collection of items, for instance in a museum, library or art gallery. This person’s primary job is to design exhibits, organize and acquire collections and do research on the artifacts included in the collection.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

friction     The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage a surface of some material as it rubs against another.

granular     Composed of granules or grains.

mechanical engineering     A research field in which people use physics to study motion and the properties of materials to design, build and/or test devices.

newton     A unit of force named for Sir Isaac Newton, a 17th century English physicist and mathematician. One newton is an amount that would give a mass of one kilogram an acceleration of one meter per second per second.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

particle     A minute amount of something.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

physicist     A scientist who studies the nature and properties of matter and energy.

resistance     (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.

robot     A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.

tack     (in sailing or in working on some project) To change course or the approach to getting something done.

tactic     An action or plan of action to accomplish a particular feat or goal.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.


Journal:​ J. Wu et al. “Elephant trunks form joints to squeeze together small objects.” Journal of the Royal Society Interface. Vol. 15, October 24, 2018. doi: 10.1098/rsif.2018.0377.