Biologists antagonised ants and found out they can hold grudges

January 12, 2025 Imma Perfetto

Previous research has shown that ant colonies are more likely to behave aggressively towards neighbouring colonies, but less likely to do so against unfamiliar ones.

It’s known as the “nasty neighbour effect” and, until now, researchers weren’t sure why it exists.

A new Current Biology study has discovered that ants remember the smell of their enemies.

“We often have the idea that insects function like pre-programmed robots,” says Volker Nehring from the University of Freiburg, Germany.

“Our study provides new evidence that, on the contrary, ants also learn from their experiences and can hold a grudge.” 

The researchers pitted colonies of the black garden ant, Lasius niger, against each other. In the first phase of the experiment, they were exposed either exposed to nestmates or to ants from a different colony.

Each meeting lasted for one minute and was repeated once per day for 5 consecutive days. Ants’ aggression when encountering non-nestmates increased significantly during this training phase.

On day 6, the team found that ants acted most aggressively when encountering the non-nestmate colony they had previously fought but were less aggressive towards ants from a non-nestmate colony they hadn’t yet encountered. Unsurprisingly, they weren’t aggressive towards their own nestmates.

In the second phase of the experiment, encounters were repeated with either aggressive or passive ants from a different colony. They found the ants that had previously only encountered passive competitors behaved significantly less aggressively.

Because ants use odours to distinguish between members of their own nest and those from other nests, the study suggests that ants learned to associate aggression with the non-nestmate colony’s specific scent.

Nehring and his team now plan to investigate whether and to what extent ants adapt their olfactory receptors to their experiences.

Originally published by Cosmos as Biologists antagonised ants and found out they can hold grudges