‘Rats cause riots!’ chanted demonstrators who forced their way into the House Galleries at the United States Congress in 1967. The American government was deliberating President Lyndon Johnson’s ‘Rat Bill’, which would allocate $40 million to the elimination of rodent infestations in inner cities. Republican opponents of the bill had presented it as a trivial and even comical matter, a Tom and Jerry concern unfit for a superpower. Couldn’t a few cats and a bit of poison do the job?

Johnson, and the demonstrators, led by civil rights champion Jesse Gray, knew better. Rats were the harbinger of urban decline and chaos. In 1963 Gray had organised protests against vermin infestations and neglect in Harlem tenements. When nothing was done, he started a rent strike. The next summer, Harlem rioted, inaugurating long years of civil disorder in American cities. Watching from beyond Washington, a growing number of experts on rats and cities were also aware that a few cats and a bit of poison weren’t up to the job. Prominent among them was John B Calhoun, who knew more about the habits of urban rats than any other person, and whose elaborate experiments on rat behaviour posed ominous questions for the modern city and for the future of human society. Calhoun’s experiments, and the wider world they were part of, are the subject of Rat City, an engrossing study by Jon Adams and Edmund Ramsden. 

Rats are tough to eliminate. During the Second World War, the city of Baltimore made an effort to tackle its rat problem by supporting the Rodent Control Project at Johns Hopkins University, which made use of novel poisons, and carefully studying the results. (Contrary to their reputation, rats are