2023-05-31 17:36:43
The desert ants (Cataglyphis fortisse) live in the salt pans of North Africa, an extremely inhospitable environment. To search for food, the foragers have to cross the desert, sometimes long distances until they find something to eat, for example a dead insect. So, they return home with their loot. In order not to get lost, they use a sun compass and a pedometer that allows them to measure the distances they cover. In addition, they possess the ability to learn and use visual and olfactory cues. “This extremely harsh habitat has led these ants, during evolution, to a navigation system with unsurpassed precision,” says Marilia Freire, a researcher at the Max Planck Institute for Chemical Ecology.
The scientist and her team have discovered that these insects use a curious orientation strategy depending on the environment. In previous studies in Tunisia, they had noted that nests in the center of salt flats, where there are hardly any visible markings, had high mounds at their entrances. In contrast, the nest hills near the brushy edges of the salt pans were lower or barely noticeable.
The researchers wondered if these visible differences serve a purpose in helping the ants better find their way home. “It’s always hard to tell if an animal is doing something on purpose or not. The high nest mounds in the middle of the salt flats could have been a secondary effect of differences in soil structure or wind conditions. However, the idea was crucial to our study: remove the mounds and provide nests with and without artificial markings, and see what would happen,” says Markus Knaden, from the Department of Evolutionary Neuroethology.
According to what they say in ‘Current Biology’, the researchers tracked the ants with a GPS device. This allowed them to track them on their way to the salt pan and back home. “We observed that desert ants are capable of traveling much greater distances than previously reported. The farthest distance traveled by a single animal was more than two kilometers. However, we also observe an unexpectedly high mortality rate. About 20% of the ants that feed no find returned home after extremely long runs and died in front of our eyes, which explains the enormous selection pressure for better targeting,” says Freire.
visual cues
Experiments in which the ants could be tracked with particular precision over the last few meters to the nest, thanks to a grid painted on the ground, showed that nest hills are important visual cues. If they were removed, fewer ants found their way back to the nest, while their mates in the nest simultaneously began rebuilding the mounds as quickly as possible.
If, instead, the scientists placed artificial landmarks in the shape of small black cylinders near the entrances to nests whose mounds they had previously removed, the ants did not set about building new ones. Apparently, the cylinders were enough for orientation.
In the anthills, the work is divided. The foraging ants are usually older and more experienced members of the nest, while the younger ants are busy building. Therefore, there must be some kind of information flow between the two groups. Researchers don’t yet know exactly how this is accomplished. “One possibility would be that the ants in the nest somehow notice that fewer foragers are returning home, and as a result, hill-building activities at the nest entrance increase,” Freire explains.
Markus Knaden has been studying desert ants for 25 years and is still in awe of their fascinating abilities: “The animals can learn visual and olfactory cues despite their small brains. In addition, they can decide what information is useful for their navigation and what is not. All this was already known. However, “the fact that they even build their own waypoints to orient themselves and only choose to invest in this work when other environmental cues are lacking is quite astonishing.”
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