Desert ants elevate nest entrances to help foraging ants find their way home

Scientists at the Max Planck Institute for Chemical Ecology have made an interesting discovery about the navigation skills of desert ants. In the absence of visible landmarks, these ants have been found to enhance their chances of finding their way back to the nest by elevating their nest entrance. This behavior was observed in ant colonies located deep within the Tunisian saltpan, where visible landmarks are scarce.

The researchers noticed that nests in the center of the saltpans had higher mounds at their entrances compared to nests near the shrub-covered edges. This led them to investigate whether these visible differences served a purpose in aiding the ants’ navigation. To test this, they removed the mounds from some nests and provided artificial landmarks for others, observing the ants’ behavior in each case.

The study’s lead author, Marilia Freire, highlighted the remarkable navigational abilities of desert ants, particularly in harsh environments. These ants utilize path integration, a navigation mechanism that combines a sun compass and a step counter to measure distances. They can also learn and use visible and olfactory cues. The challenging habitat they inhabit is believed to have contributed to the evolution of their highly precise navigation system.

While it is difficult to determine whether the ants intentionally create the elevated mounds, the study aimed to understand the purpose behind this behavior. The researchers hypothesized that the mounds could serve as self-made landmarks to assist the ants in finding their way home. By removing the mounds and introducing artificial landmarks, they sought to observe the ants’ response.

Overall, this study sheds light on yet another fascinating aspect of the navigation skills displayed by desert ants, further demonstrating their remarkable abilities to survive and thrive in inhospitable environments.

Video summary of Freire, M., Bollig, A., Knaden, M. (2023). Absence of visual cues motivates desert ants to build their own landmarks. Current Biology, doi: 10.1016/j.cub.2023.05.019 (including video material of desert ants and experiments in the Tunesian saltpans). Credit: Markus Knaden, Max Planck Institute for Chemical Ecology

In their experiments, the scientists utilized GPS devices to track the movements of the ants as they ventured into the saltpan and returned to their nest. This allowed them to observe that desert ants are capable of covering greater distances than previously believed. The longest recorded distance traveled by a single ant was over two kilometers. However, the researchers also noted a surprisingly high mortality rate, with approximately 20% of foraging ants failing to find their way back home after extensive runs, ultimately perishing in front of the researchers’ eyes. This high mortality rate highlights the immense selection pressure driving the ants to develop even more refined orientation skills, emphasizing the significance of accurate navigation.

Experiments involving precise tracking of the ants’ final approach to the nest, facilitated by a painted grid on the ground, revealed the importance of the nest mounds as visual cues. Removing the mounds resulted in fewer ants successfully returning to the nest, prompting their nest mates to swiftly rebuild the mounds. Conversely, when artificial landmarks in the form of small black cylinders were placed near the nest entrances after removing the mounds, the ants did not invest in constructing new ones. Evidently, the presence of these cylinders alone was sufficient for the ants’ orientation.

Within ant colonies, tasks are divided among members, with older and more experienced ants typically undertaking foraging while younger ones engage in construction activities. The researchers have yet to ascertain precisely how information is communicated between these two groups. Marilia Freire suggests a possibility wherein ants within the nest somehow detect a decrease in the number of returning foragers, prompting an increase in mound-building activities at the nest entrance.

Markus Knaden, who has been studying desert ants for a quarter-century, continues to be astounded by their remarkable abilities. Despite their small brains, these ants can learn and utilize both visual and olfactory cues, demonstrating their ability to discern which information is relevant for navigation. While these traits were already known, the discovery that the ants construct their own landmarks for orientation and selectively invest in this behavior when other environmental cues are lacking is a particularly surprising revelation.

Source: Max Planck Society

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