This article explores the conflicts between people and Atta leafcutter ants over the meaning of anthropogenic deforestation in nineteenth-century Brazil. As human agricultural settlement advanced, ants followed in its wake, harvesting leaves, flowers, fruits, and other plant parts from crops to supply their underground fungus gardens. In so doing, the ants, as semiotic selves, interpreted what humans had done and acted accordingly, producing historically consequential environmental change in the process. An examination of primary sources such as legislation, travel journals, agricultural manuals, government administrative documentation, and newspapers for human-ant conversations demonstrates how interspecies sense making has fueled social innovations and rearrangements, shaping technical developments, legal-administrative practices, parliamentary discussions, and even local electoral arenas. By taking written documents as surviving structures of embodied, more-than-symbolic conversations, this analysis both takes its cue from, and helps substantiate, what Ewa Domanska has termed a “multispecies co-authorship” approach to human-animal relations. It argues that such a theoretical-methodological stance helps environmental historians account for nonhuman agency by allowing the exploration of animals’ truly creative, rather than merely resistive, behavior.