The biosphere is a network of interacting species that connects organisms across all scales, from microbes to mammals. Knowledge of the mechanisms underlying these relationships, and the evolutionary forces that shape them, is fragmentary. In this lecture, I will describe how my lab has pioneered the study of rove beetles as a model clade to break open basic problems in organismal interactions and their evolutionary origins. Most of the 66,000 rove beetle species are free-living predators. Yet, from this ancestral lifestyle, hundreds of lineages have transformed into symbiotic organisms specialized for life as imposters within the complex societies of ants. The transition from free-living to symbiotic embodies evolution in the extreme, with dramatic changes in social behavior and chemical communication that enable rove beetles to assimilate into the social fabric of host colonies. The widespread, convergent evolution of this form of symbiosis, combined with the experimental tractability of both free-living and symbiotic rove beetles, provides a virtuoso system for understanding both how and why new ecological relationships are forged by evolution. I will discuss how my lab’s work is creating an integrated picture of how species recognize and interact with each other, illuminating the conditions that predispose such interactions to emerge, and pinpointing forces that shape the evolutionary path towards obligate and highly intimate relationships between species.