Chimpanzees are the only great apes, apart from humans, that have adapted to living on savannas as well as in forests. However, it is not yet well understood how the harsh ecological conditions of the savanna — compared with those of the forest — affect the foods that chimpanzees eat and how they do so. Now, a study led by the University of Barcelona and the Jane Goodall Institute Spain (IJGE) reveals for the first time the strategies of savanna chimpanzees for making tools and extracting the aggressive army ants — also known as
marabunta — from their underground nests and eating them in these dry, hot habitats.
The paper, published in the journal Scientific Reports, is led by Andreu Sánchez-Megías and R. Adriana Hernández-Aguilar, from the UB’s Faculty of Psychology and the IJGE. The team includes Laia Dotras and Jordi Galbany (UB and IJGE) and Adrián Arroyo, from the UB’s Faculty of Geography and History and the Institute of Archaeology (IAUB), as well as experts from the Max Planck Institute for Evolutionary Anthropology (Germany) and the University of Copenhagen (Denmark).
To date, only the feeding strategies of chimpanzees in forest habitats had been described. The new study, carried out in Dindefelo, a savanna site in Senegal, reveals that, to avoid the painful bites of army ants, chimpanzees use stick tools — with peeled bark or frayed ends — from eight plant species (mainly lianas). The primates put the tools in their mouths and cut the tool tips with their teeth. Since one of the selected plant species has chemical compounds with reported calming effect, the authors hypothesized that the chimpanzees could be selecting specific plant species to protect themselves from the painful ant bites. The study shows that eating these insects is a challenge for the primates and involves a long and complex learning process.
A nutritious food in a harsh habitat
Army ants are insects high in protein and minerals, which form the largest insect colonies on Earth. Thus, they represent a key food source for chimpanzees in various parts of Africa. In this study, the team analysed 156 events of chimpanzees eating army ants from ant nests between 2018 and 2022 in Dindefelo, in southeastern Senegal.
Although it may be more difficult to find ants in a savanna than in the forest, the study found that “chimpanzees in this savanna site did not have any strategy for extracting ants that differs from those described for chimpanzees in forests”, notes Andreu Sánchez-Megías, first author of the article, researcher at the Department of Social and Quantitative Psychology and La Caixa Foundation doctoral student at the UB.
“We found that that chimpanzees across Africa adapt their ant-consumption strategies depending on the aggressiveness of the targeted army ant species,” the expert explains.
This study is part of a project that recently discovered that the same chimpanzees revisit specific ant nests throughout multiple years to look for ants, something that had not been reported before (Communications Biology, 2024).
Understanding human evolution and protecting these endangered primates
Adriana Hernandez-Aguilar, Serra Hunter professor at the UB, supervisor of the study and co-director of research at IJGE, emphasizes that “studying chimpanzees in savanna habitats, such as the site where we conducted the study, has important implications for understanding human evolution, since the first hominin species that would eventually give rise to our lineage evolved in similar habitats.”
Researchers also warn that chimpanzees in West Africa are critically endangered. “Therefore, it is crucial to understand the strategies they use to survive in these harsh habitats where food, water and shelter can be scarce during the long dry season,” the team concludes.