Ants in the Saharan Desert are famous for finding their way home in a seemingly sparse and featureless desert. It’s called wayfinding. How do Desert Ants find their way home?

Desert Ants (Cataglyphis fortis) build landmarks to help them find their way home. What kind of landmarks?

Scientist Markus Knaden from the Max Planck Institute for Chemical Ecology in Germany, and his colleagues, studied the Desert Ant in the salt flats of Tunisia in Saharan Africa.

The scientists watched the Desert Ants travel long distances to collect food to bring back to the ant colony in the ant nest. Their ant nests were located at the edge of the salt flats where there were low scrubby desert plants. The entrances to their underground ant nests were the size of a human thumb-nail – so small in a such a vast desert.

The scientists followed the Desert Ants belonging to 16 ant nests with a GPS locator. They found that a lot of ants died during the foraging journey. During the longest journeys to find food, about 2 kilometres (1.2 miles) in distance, around 20% of ants died in the desert heat.

They noticed that the Desert Ants built mounds – anthills to act as landmarks – of various sizes and heights. When they investigated the mounds, they found that the mounds near the ant nests at the shrub-covered edges of the salt pan were barely noticeable because they were so small. The mounds in the centre of the salt flats were the tallest – taller than 25 centimetres (9 inches).

The scientists removed some mounds near the ant nests, while leaving others untouched. They found that if the mounds were not there, a lot more ants died – between 250-400% more. The surviving ants began rebuilding the mounds very quickly. It took all night to rebuild a mound even though hundreds of ants took part in the construction. 

When the scientists replaced the mounds with artificial mounds (landmarks), such as black cylinders the size of large fire extinguishers, the ants did not rebuild any new mounds. Mounds take a long time to rebuild, so they don’t do it if they don’t need to do it. With the artificial mounds, the ants marched directly home, and fewer ants died in the heat.

Therefore, scientists think that Desert Ants construct mounds to help them navigate the featureless landscape of their Saharan home, reports the New Scientist in May 2023. The mounds are navigational landmarks. 

Now the scientists want to know how the ant colony keeps track of when it needs new landmarks. Are older ants communicating to the young mound-building ants that they need new landmarks? Or are young mound-building ants taking the initiative to build new landmarks when they see their older colony members struggling to return home, and dying along the way?

Journal reference: Current Biology DOI: 10.1016/j.cub.2023.05.019

Photographer: Markus Knaden, Max Planck Institute for Chemical Ecology

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