Walk this way: desert ants move backwards with heavy loads, study finds

Study shows that deserts ants can walk and navigate backwards when moving oversized food, a discovery that could inform robotics, researchers say

Naomi Stewart

Wednesday 20 July 201623.00 BST

There comes a time in a desert ant’s life when a piece of food is too large to ignore, but too heavy to lift, and the only way to get it home is to adopt a new style of walking.

The long-legged and speedy Cataglyphis fortis normally covers ground with a three-legged stride that moves two legs forwards on one side, and one on the other. For the next step, the insect mirrors the move with its other three legs.

But recordings of ants in the Tunisian desert reveal that when faced with oversized lumps of food 10 times their own weight, the forward “tripod” walking style is abandoned. Unable to lift the morsels in their mandibles, the ants drag the food backwards instead, moving all six legs independently. “This is the first time we have seen this in any ants,” said lead author Sarah Pfeffer at the University of Ulm in Germany.

The ants’ long legs already help keep their bodies away from the scorching desert floor and enable them to speed around at up to 60cm per second.

“Think of Usain Bolt, who has very long legs compared to body size. The desert floor is also very hot, so the further away their bodies are from the surface, the better,” said co-author Matthias Wittlinger. The ants have also evolved to function at body temperatures of 50C in a desert where temperatures can soar to 70C. “They’re basically just trying to get out of the heat,” he added.

But more intriguing to the researchers was the ants’ skill at navigation. “At any point, they know the direction and distance back to their place of origin. Most ants are capable of this, but desert ants live in dried out salt lakes, which are flat and bare,” said Wittlinger. When they drag food backwards though, the ants cannot see where home is at all.

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