Muscular manoeuvres Patrice Correia/Biosphoto/FLPA

A captive African elephant called Kelly has helped to shed light on one of nature’s great mysteries: how elephant trunks that can grip and carry heavy logs a metre across can also handle tiny, fragile objects.

Jianing Wu at Georgia Institute of Technology in Atlanta, and his colleagues, offered Kelly items of food in four different sizes – powdered bran, cubed bran, cubed swede and largest of all, cubed celery.

“We wanted to know how she would grab food items of different size,” says Wu.


They offered the food on a table that measured the downward force her trunk generated during gripping, and took detailed measurements of Kelly’s trunk manoeuvres to find out how she varied the shape of her trunk and the forces it applied to grip each target.

Kelly’s secret, it turns out, was her ability to create a kink at any point along her 2-metre-long trunk that would provide exactly the right downward force to grip each size of food item.

The kink acted like a joint that subdivided her trunk into two sections: a long section that supported the weight of the trunk and a short tip pointing vertically downwards for dexterous gripping.

Force fine-tuning

Wu and his colleagues found that Kelly could reduce the downward force for particularly delicate object handling by making the vertical part of her trunk shorter – and increase the force by making the vertical section longer.

In other words, Kelly had the ability to fine-tune how much force to apply by altering the position of the “kink” in her trunk.

Counterintuitively, as objects became smaller, Kelly needed more force to pick them up. Most tricky was the bran powder, which she had to compress almost into a solid first before she could pick it up.

“For the smaller particles, she sweeps, scoops and squeezes the food to pick it up,” says Wu, who presented his team’s results at the annual meeting of the Society for Integrative and Comparative Biology in New Orleans last week.

Armed with the insights, Wu’s team is hoping to build a small prototype artificial gripper based on the same principles. “If we know how an elephant manipulates its trunk to handle such a huge range of objects, we may be inspired to develop a universal robotic gripper,” he says.

It won’t be easy, because existing artificial muscle technology would struggle to match the complexity of the muscular manoeuvres within the trunk. But Wu thinks that eventually it could result in soft but highly versatile robotic gripping devices for use in industry and perhaps for delicate rescue operations.