Imaging the building blocks of ant pheromone communication
Organisms have evolved diverse strategies to communicate. Beyond acoustic and visual signals, many species rely on chemical communication, including pheromones: volatile compounds involved in reproduction, defense, and coordination. Ant trail systems, a paradigm of pheromone use, have inspired decades of research in collective behavior, self-organization and optimization algorithms. Yet, despite their central role, individual pheromone deposits have never been directly visualized or quantified, limiting our understanding of how deposition events scale into collective trail formation. Here, we use interferometric imaging to reveal and quantify single pheromone deposits in the ant Lasius niger. This label-free, non-invasive approach enables precise measurement of single deposit volume (~1 pL, with x20-fold variability), morphology, and temporal dynamics. We uncover a two-phase volume loss process: most of secreted volume evaporates within seconds, forming a dried droplet, which then partially sublimates (~10%) over one hour. These findings challenge the assumption of homogeneous deposition and bring previously inaccessible properties of ant pheromone trails within experimental reach. Our method establishes a quantitative framework for studying the spatiotemporal dynamics of insect chemical communication, linking individual signaling to collective patterns.