Chimpanzees use different types of memory to find insects hidden underground, study finds

Chimpanzees are the animals with the most complex memory, apart from humans. They remember where and when ripe fruits are available, and use this information to decide which trees they will visit and even where they will sleep in order to eat these fruits first thing in the morning. However, the cognitive strategies they use to find foods of animal origin rather than plant origin are not yet well understood.

Now, experts from the University of Barcelona and the Jane Goodall Institute Spain have led a study that describes the previously unknown cognitive skills deployed by wild chimpanzees in Africa to eat army ants that hide in hard-to-locate underground nests. This is the first paper to describe how these primates make use of spatial and episodic-like memory to extract social insects from nests hidden underground.

The study reveals for the first time how chimpanzees can successfully meet a cognitive challenge to exploit an animal food source in the wild for years.

The findings, published in the journal Communications Biology, expand our understanding of the cognitive strategies of non-human primates, and provide new insights for reconstructing the evolution of cognitive abilities in our lineage.

Army ants (Dorylus spp.), also known as the fearsome marabunta, form the largest colonies of social insects on the planet. These hymenopterous insects are rich in protein and minerals—key nutrients for chimpanzees—but are very difficult to find because they nest under rocks, roots and fallen vegetation and move unpredictably.

As part of the study, the team analyzed a total of 679 chimpanzee visits to four army ant nests that occurred from 2018 to 2022 in the Dindefelo community nature reserve, a savannah habitat in the south-east of Senegal.

Andreu Sánchez-Megías, Ph.D. student and first author of the article, says, “We studied if chimpanzees intentionally return to nests, the strategies they use to detect if ants are present, the availability of these insects and the extent to which chimpanzees consume them.”

He notes that the ant nests “are scarce and nearly always impossible to see, and thus, for the chimpanzees, remembering the exact location of the nest is a good foraging strategy. The nests are abandoned and reoccupied at irregular intervals, and this key component of the ants’ behavior allows chimpanzees to repeatedly visit the same nests to feed on these insects.”

Sight, smell, taste and touch

It seems that these apes remembered previous visits to ant nests and modified their behavior depending on whether they had encountered the insects on previous visits. The findings indicate that chimpanzees use spatial memory to remember the exact location of hidden ant nests, and episodic-like memory to remember whether they found ants on previous visits to the same nests.

Episodic-like memory is the ability to remember where, when and what happened in past experiences, and is named after episodic memory in humans, which consists of the same abilities plus the ability to verbalize memories. Because non-human animals cannot explicitly communicate to us what they remember, this ability equivalent to human episodic memory is called episodic-like memory.

Furthermore, it is noteworthy that this is the first study to describe how chimpanzees use four senses (sight, smell, taste and touch) to inspect empty nests and detect if there are ants.

Importance for conservation and for understanding human evolution

Serra Hunter professor R. Adriana Hernandez-Aguilar says, “It is important to emphasize that the study of chimpanzee cognition in an ecologically relevant context—such as the savannah where our research was carried out—contributes to better understanding the evolution of human cognitive capacities, given that the first hominins inhabited similarly dry, open, and hot landscapes.”

“Chimpanzees are an endangered species and learning more about the strategies they use to obtain important foods in the wild helps us to conserve them,” the researchers conclude.