Bad experiences may influence future interactions between neighboring ant colonies. Credit: Deposit PhotosShareIts not just humans who have trouble making amendsEarths 20 quadrillion ants arent 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 Germanys University of Freiburg indicates ants dont just react in the momentthey retain knowledge of hostile encounters with neighboring enemies, and act accordingly.Ants rely on their olfactory sense to navigate much of the world around them. Credit:Current Biology 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 antseither 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 colonys 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. Get the Popular Science newsletter Breakthroughs, discoveries, and DIY tips sent every weekday. By signing up you agree to our Terms of Service and Privacy Policy.These unwanted run-ins dont 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, Nehrings 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 ants 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 nests 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.