ABSTRACT This article examines a technoscientific project for eradicating the North American beaver in Tierra del Fuego (TDF), an austral region known as “The End of the World.” Introduced from Canada into TDF in 1946 to promote a fur industry, beavers are today classified as an alien and invasive species that severely threatens the pristine native ecosystems of TDF. We analyze the environmental history of beavers in TDF to explore the many partial losses that have shaped beaver-human relations across hemispheres. We argue that various ends of the world have mediated different technoscientific responses to beavers’ vitalities, reflecting multiple forms of human anxiety over loss and extinction. Thinking with the beavers and their environmental history in TDF, we explore the “Castorcene” as the human anxiety that emerges from beavers' vitalities. As an analytical concept, the Castorcene de-universalizes the Anthropocene, decolonizes extinction horizons, displaces human exceptionalism, and situates and singularizes imaginaries of the end of the world.