The Great Hanoi Rat Massacre of 1902

Bounty Scheme

The French administration in Hanoi devised a rat bounty program to tackle the city's rat infestation in 1902. Initially, rat hunters were employed to kill rats, but the overwhelming number of dead rats led to a shift in strategy: a bounty for rat tails. This change led to an influx of rat tails, but also to a peculiar problem. People began cutting off tails and releasing the rats to breed more, even importing and breeding rats for profit.

People were catching rats and cutting off their tails to turn in for the bounty. But they weren't killing the rats. Why weren't people killing the rats? Because they wanted the rats to breed so there would be more rats that they could harvest for tails.

--- Gary Arndt

The program, intended to reduce the rat population, inadvertently encouraged its growth, highlighting a critical flaw in the plan 1.

   

Program Failures

The failure of the rat bounty program in Hanoi is a classic example of the cobra effect, where incentives backfire. Similar to a British program in India, the bounty led to breeding rather than eradication. This phenomenon is not unique; history is rife with such perverse incentives, from Canadian orphanages to Afghan poppy fields.

The great Hanoi rat massacre is a textbook example of what economists call the cobra effect, or perverse incentives.

--- Gary Arndt

Despite the program's failure, the French governor, Paul d'Omer, later became the president of France, while Hanoi suffered a bubonic plague outbreak in 1906, likely spread by rats 2.