Ant Fight Club: A Pilot Study on the Impact of Caffeine on Aggressive Behaviors

Abstract

Background: In the absence of a leader, some ant species resolve social hierarchy through dueling tournaments that yield a pseudo‑queen. Prior work suggests caffeine can increase linear speed and conditioning in ants, potentially altering competitive interactions. Our research aims to test whether caffeine exposure increases aggressive fighting behavior during dueling tournaments in harvester ants.

Methods: We compared caffeine‑exposed (“experimental”) and non‑exposed (“control”) ants across three fighting formats: 1 control vs. 5 experimental, 5 control vs. 1 experimental, and 5 control vs. 5 experimental. We observed aggressive behaviors (e.g., bites) and non‑aggressive interaction patterns (e.g., huddling, exclusion, group preference) during standardized trials.

Results: Aggressive acts were rare overall: only two bites were recorded, both by control ants, providing no evidence that caffeine increased aggression. In 1C:5E fights, the single control ant displayed higher activity/energy, while experimental ants huddled in smaller groups and excluded the control from joining—a clear avoidant pattern toward the control. In 5C:1E fights, similar behavior occurred where control ants huddled in groups of 2–3 and excluded the single experimental ant. In 5C:5E fights, ants preferentially interacted within their own treatment group, suggesting ingroup clustering rather than overt aggression.

Conclusions: Caffeine exposure did not increase aggressive fighting behavior in these dueling contexts. Instead, we observed avoidance and ingroup clustering that varied with group composition, while aggressive acts were infrequent and confined to controls. These findings refine expectations about how stimulants influence ant social dynamics, pointing toward changes in social spacing and group preference rather than escalation of aggression.