Apparently, desert ants “know” how well their scouts can use landmarks to find their way home to the nest. This is reflected in the results of an experimental study. The crawlers therefore only expand their mounds to provide orientation aids for returnees that are visible from afar. If, on the other hand, there are already other landmarks in the vicinity of the nest entrance, the state does not invest in the costly construction of the portal. So far, the scientists say it remains a mystery what the desert ants' resource-saving calculations are based on.
A bunch of scurrying tiny creatures, but not a trace of chaos: Thanks to sophisticated control systems, an ant colony forms a complex unit with amazing performance. Such a superorganism can even produce collective intelligence - the community behaves in a way that seems almost magical, studies show. Research into the desert ants of the species Cataglyphis fortis has focused primarily on the astonishing ability of these inhabitants of the salt pans of North Africa to find their way around. They live in subterranean nests, the entrance area of which can be noticed by small mounds. Some are almost 30 centimeters high, while in other nests the elevation is extremely flat or barely visible.
Mastering the orientation on the trail
In order to provide food for the colony in the barren habitat, scouts march far from the nests into the surrounding countryside. Scientists from the Max Planck Institute for Chemical Ecology in Jena have been researching for some time how the ants manage to find their way back to their nest after their reconnaissance trips. "We believe that this extremely harsh environment has evolved into a navigation system of unmatched precision," says lead author Marilia Freire. As she reports, some exciting aspects of orientation skills have already been pointed out. In the sandy environment, the insects apparently cannot follow their own scent trail. Instead, they use a sun compass to set the running direction. In principle, it has also already been shown that they use olfactory, but also visible landmarks as clues.
The basis of the current study was the finding that the nests in the middle of the salt pans, where there are particularly few visible landmarks, have comparatively high hills at the nest entrances. The hills near the bushy edges of the salt pans, on the other hand, seemed lower or absent. The researchers wondered whether the high hills in the barren areas could perhaps serve as a guide for the ants on their way home. “It is always difficult to tell whether an animal is doing something purposefully or not. The high nest mounds could also have been a side effect of the different soil structure or the different wind conditions," says senior author Markus Knaden. The researchers therefore decided to investigate the question experimentally. "To do this, we removed some hills, then provided some nests with artificial landmarks, others not, and then observed how the ants react to them," says Knaden.
Only if necessary, will be built
For the experiments, the researchers also followed the scout ants using GPS technology. "We observed that desert ants are able to travel far greater distances than previously reported. The furthest distance traveled by a single animal was more than two kilometers,” reports Freire. The researchers were also able to document a surprisingly high mortality rate: around 20 percent of the foraging ants did not manage to return.
It turned out that the hills near the nests in the particularly barren regions apparently ensure that the losses are not even higher. They form important visual orientation aids, the results show. When they were removed, fewer ants found their way back, while at the same time their nestmates began rebuilding the mounds as quickly as possible. Amazingly, that was not the case when the scientists placed 50-centimetre-tall cylinders near the nests from mounds they had previously cleared away. Then the ants did not invest in the construction of new mounds. Apparently, the peoples "understand" somehow that they already have sufficient orientation aids with these cylinders.
As the researchers explain, there could be an exchange of information between the foraging ants and the construction ants. "One possibility would also be that the nest is perceived to be declining in the rate of returnees, and as a result activities to build the nest mound are intensified," Freire speculates. Ultimately, however, the basis of the ability remains a mystery so far. Knaden concludes: "It is amazing that desert ants even build their own landmarks for orientation and only decide to do this work if other orientation aids are missing," says the scientist.
Source: Max Planck Institute for Chemical Ecology, Article: Current Biology, doi: 10.1016/j.cub.2023.05.019