Ants Learn From Experience and Can Hold Grudges, Study Finds

Like humans, animals experience complex emotions like empathy, love, grief and joy. They can also hold grudges.

In a recent study, a team of biologists found that ants can learn from experience and hold grudges when confronted with competitors from another nest with whom they’ve had previous negative experiences.

“We often have the idea that insects function like pre-programmed robots. Our study provides new evidence that, on the contrary, ants also learn from their experiences and can hold a grudge,” said Dr. Volker Nehring, an academic counselor in the Department of Evolution and Ecology at Germany’s University of Freiburg, in a press release from the university.

Nehring co-led the research team with doctoral student Mélanie Bey.

The team put the ants in the experiment in confrontations with rivals from another nest. The study ants remembered negative experiences they had had during earlier encounters, behaving more aggressively toward ants they had experienced as aggressive than they did toward ants from unknown nests.

Additionally, when they came upon ants from a nest they’d previously encountered who were passive, they were less aggressive.

Ants distinguish between their own nest members and ants from other nests using odors, with each nest having its own unique scent.

Earlier studies have demonstrated that ants behave especially aggressively toward their closest neighbors. They are particularly likely to bite members of neighboring nests with their mandibles, or even spray acid to kill their competitors.

Ants from nests that are further afield are less likely to be subjected to such aggressive maneuvers. But until now, it wasn’t clear why.

The researchers found that ants remember their attackers’ smell, which causes them to be more aggressive when faced with competitors from familiar nests.

The experiment was carried out in two phases. The first involved ants having various experiences: One group had an encounter with their own nestmates, while the second encountered aggressive ants from rival nest A. The third group were faced with another group of aggressive ants, this time from rival nest B.

There were five encounters on consecutive days, each lasting one minute.

“In the subsequent test phase, the researchers examined how the ants from the different groups behaved when they encountered competitors from nest A. The ants that had already been confronted with conspecifics from this nest in the first phase behaved significantly more aggressively than those from the other two groups,” the press release said.

In order to find out how much the ants’ higher aggression was a response to the behavior of rivals from a particular nest, the research team modified the experiment.

“In the first phase, they now distinguished between encounters with aggressive and passive ants. They ensured that an ant behaved passively by cutting off its antennae. In phase two of the experiment, the ants that had previously only encountered passive competitors behaved significantly less aggressively,” the press release said.

Next, Nehring and colleagues plan to look into if and how much ants modify their olfactory receptors in response to their experiences.

The study, “Associative learning of non-nestmate cues improves enemy recognition in ants,” was published in the journal Current Biology.