From 1942 to 1952, a programme took place at Johns Hopkins to devise new methods of controlling Baltimore’s rat population. This article focuses on three individuals closely connected to this project at various stages of its development: psycho-biologist Curt Richter, animal ecologist David E. Davis, and ecologist and psychologist John B. Calhoun. For all three, the challenges of controlling rat numbers highlighted the significance of stress – a homeostatic mechanism critical to the survival of the animal. This was a process (...) that was analyzed and manipulated by (re)introducing the wild rat into the laboratory. Here the rat not only contributed to new methods of rodent control, but offered new possibilities for the control and improvement of humankind. Yet it was not just the animal, but the physical structure of the laboratory that came to model the world outside. Through examining the experimental systems of the three scientists, this article will trace a series of transgressions between laboratory and field, urban and wild, animal and human. The result was that while animals were used to model the behaviour and pathologies of human city dwellers, the laboratory spaces in which they existed came to model the urban environment. We shall also see how differing perspectives on the value and uses of animal models and environments encouraged and reinforced alternative visions as to the role of science in the service of the city. (shrink)