After a series of conquests between 1859 and 1885, Vietnam found itself under French colonial rule. The systematic infusion of French cultural ideals was strong, and some cities, such as Hanoi, became specifically targeted for colonization — a city to stand as a beacon to French ideals and hygiene for the supposedly backward, unmodernized Vietnamese. Aristocratic neighbourhoods were constructed or retrofitted for the new inhabitants arriving from France, with villas, treed boulevards, and all the amenities of contemporary French architecture — all built with the sweat and blood of the conquered Vietnamese.
In order to import all the modern comforts of home, elaborate sewer systems were constructed. But this feature of French urban design quickly created new problems: the sewers became a breeding habitat for insects, pests, and especially, rats. Now, sheltered from predators on the surface above, the rats could procreate and relocate throughout the city faster than ever before. They could even gain direct access into the homes of the elitist colonizers themselves.
By 1902, the situation was becoming hazardous, and the administrators of the city began hiring poor, desperate Vietnamese labourers to hunt the rats. Although thousands (and sometimes tens of thousands) of rats were killed every day, the city realized that the eradication project was not eclipsing the birthrate of the rodents. They had not even put a dent in the population.
In desperation, the colonial regime issued a bounty — one cent per rat tail. At first, the financial incentive seemed successful. Residents from all over the city brought in rat tails by the hundreds of thousands. But still, perplexingly, the rat numbers continued to rise.
The incentive program had completely backfired: officials discovered that city residents had been harvesting rat tails, but then letting the critters go free — presumably to mate and produce more rat tail for their one cent redemption! Tail-less rats became a common sight throughout the city. Furthermore, industrious residents in the suburbs of the city actually began farming rats in order to cash in on their tails.1
In the end, the incentivization scheme to eradicate the rats resulted in multiplying their population. In economic terms, the rat tail bounty established a perverse incentive.
Vann, Michael G. (2003). Of Rats, Rice, and Race: The Great Hanoi Rat Massacre, an Episode in French Colonial History. French Colonial History. Vol 4. 2003, pp. 191-204. ↩