In the 1990s, a graduate student named Michael Vann was working through French colonial records in Aix-en-Provence, ten dossiers a day, on the history of Hanoi. Tax documents. Road building. By his own account, he got very bored. One afternoon he pulled a file because of its title: “destruction of animals in the city.”
Inside were about 100 to 120 printed sheets of daily rat kills from the spring and summer of 1902, district by district. Five hundred on the first day, he recalls. Then 700, then 1,000, then 5,000 and 8,000. The high point, as he reads the records, was June 12: 20,114 rats.
The story behind the sheets starts with sewers. Around the turn of the century the French rebuilt Hanoi as a showpiece capital, and the French quarter got modern sewers. Rats found them a fine place to breed, and, Vann says, started coming up through the toilets of French villas. Plague had reached Hong Kong. Officials panicked.
Vietnamese workers were sent into the sewers to kill rats. The colonial government also offered a bounty to anyone in the city. Nobody at city hall wanted to receive thousands of dead rats, so the proof required was the tail. The payment, in Vann’s telling, came to about a penny a tail.
Tails arrived by the thousands. The authorities believed they were winning.
About three months in, officials noticed rats running around just outside Hanoi with no tails. Further investigation found rat farms in the villages on the city’s edge. People were raising rats, cutting off the tails for the bounty and releasing the animals to breed. A black market moved rats around northern Vietnam so their tails could be cashed in at Hanoi.
“They were furious that they got outsmarted,” Vann said of the French, “and they were furious that they’d been spending all this money and it’s actually increasing the number of rats in Hanoi.”
What came next was not funny. According to Vann, the authorities turned to harsher methods. In one case they surrounded a house with a pit of lye and set the building on fire, and burning rats came running out. Officials burned houses and took bodies away. Vann found police reports of protests across the city. If the body is taken away and destroyed, he explained, the family has no way to venerate its ancestor.
Vann published the story in 2003 and assumed a few dozen colleagues had read it. In 2012 the producers of Freakonomics called.