It’s not just humans who have trouble making amends—Earth’s 20 quadrillion ants aren’t quick to forgive, either.
Ants primarily rely on their fine-tuned olfactory sense to differentiate between the smell of members of their own family (i.e. safe ants) and ants from other colonies. A familiar scent while out foraging, for example, allows a worker ant to know which nearby ants are there to help, and which may be rivals hunting for the same resources. But new research from evolutionary biologists at Germany’s University of Freiburg indicates ants don’t just react in the moment—they retain knowledge of hostile encounters with neighboring enemies, and act accordingly.
According to their study published in Current Biology, scientists conducted two phases of experiments to determine if ants remember bad experiences with other ants, and how it influences their relationships. First, they placed ants into 60 second meet-and-greet scenarios: In one setting, the insects simply encountered some of their nestmates; another situation involved a group interacting with aggressive ants from “Nest A,” while a final group met yet another set of hostile bugs from “Nest B.” This was then repeated once for each group over five consecutive days. From there, scientists examined how the various ant groups subsequently reacted when they encountered the aggressive Nest A ants—either for the first time, once again, or in comparison to Nest B bugs.
Further analysis showed ants were more hostile towards ants that smelled of past bad encounters with other nests. When they re-crossed paths with a more passive colony’s ants, however, the insects tended to behave more calmly.
“We often have the idea that insects function like pre-programmed robots,” says research associate and study co-author Volker Nehring in an accompanying statement. “Our study provides new evidence that, on the contrary, ants also learn from their experiences and can hold a grudge.”
These unwanted run-ins don’t devolve into crude gestures or rude exchanges. Ant throwdowns involve the use of their sharp mandibles, and can even leave a bad taste in their mouths, literally. Anger ants enough, and they spray formic acid at one another. While often deadly to the insects themselves, Nehring’s team made sure to break up the fights before things got too heated. (A telltale sign of incoming formic acid is the bending of an ant’s bulbous end segment known as the “gaster.”)
In their study, Nehring and colleagues conclude that associative learning “plays a crucial role in the formation of both nestmate and non-nestmate recognition templates,” and that aggression can function as an unconditioned stimulus likely associated with enemy odor labels. “This type of template learning can help explain different patterns of variation in nestmate recognition, from nasty neighbor effects to task- and age-specific variation in aggression,” the team adds.
Researchers also believe these results imply ants associatively learn olfactory classifiers for ants outside their colonies, which may help tailor defensive responses depending on a nest’s intruders. Moving forward, the biologists hope to look into how much ants can adapt their olfactory receptors based on these interactions to see if the knowledge translates on an even deeper level.
