In 1995, Michael G. Vann was researching for his doctoral dissertation on the city of Hanoi under French colonial rule in the overseas archives in Aix-En-Provence when he stumbled across one of the more bizarre primary sources a historian is ever likely to find. Buried deep within the archives was a folder labelled ‘Destruction of Hazardous Animals: Rats‘.

For Vann, who had spent weeks wearily sifting through the archives, this strangely titled file proved too great a temptation. He had to know what happened to those poor rats.

In the file was a haphazard collection of records from the French government of Indochina (modern Vietnam, Cambodia and Laos) detailing the number of rats killed on each day and the amount of money paid out to the rat hunters.

This is the story of the Great Hanoi Rat Hunt.


France formally assumed control of Hanoi in 1882, occupying the city after the failure of the Treaty of Saigon. However, northern Vietnam (known amongst the French as Tonkin) was not fully pacified until 1896.

Paul Doumer
Paul Doumer

A year later, Paul Doumer arrived in Hanoi as the newly appointed Governor-General of Indochina. Under his leadership, Hanoi would be transformed. Prior to the French occupation, Hanoi had been a collection of 36 streets, each devoted to a specific craft. The settlement also possessed a citadel and fort, ironically constructed in 1802 with the assistance of French military engineers trained in the Vauban tradition of fortification. Several temples and pagodas also littered the city. However, in the eyes of the French, Hanoi was little more than a dirty, squalid, ramshackle collection of villages. For them, if Hanoi was to become a city worthy of the French colonial empire, this had to change and with the arrival of French administrators in the 1880s, particularly Paul Bert in 1886, this process began in earnest.

St Joseph's cathedral
St Joseph’s Cathedral

Large areas of the settlement, including most of the citadel and many temples, were demolished to make way for colonial buildings. Most notable among these were St Joseph’s Cathedral and the Lanessan Hospital.

However, following the arrival of Paul Doumer, the transformation went into overdrive. He planned to make Hanoi the capital of French Indochina and thus he insisted that it must look the part. To this end, a large palace was constructed as the official residence of the Governor-General of Indochina. A huge swathe of the city was cleared and rebuilt in the French style, with broad tree-lined boulevards, colonial-style villas and well-tended gardens. This became known as the French Quarter (now the Ba Đình District) and it is still known today for its beautiful architecture. Indeed so distinctly French was the French Quarter that some visitors observed that it almost felt like a slice of Paris on the other side of the world. This contrasted starkly with the cramped, narrow, chaotic Native Quarter, where the Vietnamese resided.

Presidential palace
Presidential Palace

The French Quarter was joined by the Hôtel Metropole, the Indochina Medical College, the Grand Palais d’Expositions (built for the Hanoi exhibition in 1903) and the Paul Doumer Bridge (now known as Long Bîen Bridge), which spanned the 1,700m width of the Red River. However, perhaps the most important of Doumer’s projects, both for this story and as a symbol of French modernity, was the construction of a massive underground sewage system.

By the time Doumer departed Vietnam in 1902, over 19km of sewers had been built, the largest concentration of which lay beneath the French Quarter. After all, proper sanitation was essential in keeping the colonial district clear of human waste.

Unfortunately for the French in Hanoi, the wondrous sewer system resulted in the rise of an unforeseen enemy: rats.

The Hunt

Rats had always been present in Hanoi, just as they were in almost every settlement of a decent size across the globe. However, thanks to the new sewer system, the rodents of Hanoi were about to enter something of a Golden Age.

Sewers represent an almost perfect habitat for rats. Food is plentiful and, perhaps more importantly, there is an almost complete absence of predators. Combine these two factors with the fact that a single pair of rats can produce 5 litters a year with an average of 7 but as many as 14 offspring per litter and you get an exploding rodent population.

Rats have long been reviled by many different peoples but in the 1890s this revulsion took on a new dimension: fear.

Xenopsylla cheopis, the plague-carrying flea

In 1894, Dr Alexandre Yelsin, who later became the first headmaster of the Indochina Medical College, identified the bacillus, the Yersinia pestis, responsible for bubonic plague (the contagion of Black Death fame). In 1897, Dr Paul-Louis Simond identified the flea, carried by infected rats, as the vector by which the bacillus is transmitted from rat to human. Word of these discoveries spread rapidly across the world, which at the time was in the midst of the Third Pandemic (also known as the Modern Pandemic), which would ultimately kill around 10 million people.

So when rats started making their way above ground with steadily increasing frequency in the French Quarter in 1902, the news was greeted with something approaching panic amongst the officials of the Indochina government. Soon enough, matters became worse when reports of a bubonic plague outbreak began to emerge. Worse, the outbreak appeared to be confined to the French Quarter.

For government officials, this could not be tolerated. They responded by hiring and dispatching Vietnamese rat catching teams into the sewer system. After all, kill the rat and you deny the plague-carrying fleas their transportation. The hunters were to be rewarded in proportion to the number of rodents they destroyed. It was the records of their activities that Vann discovered in the Aix-En-Provence archives.

This was unpleasant work, to say the least. The hunters had to descend into the dark, cramped sewer system, wading through human waste to hunt down a creature that may be carrying fleas with bubonic plague. All this for a reward of 1 cent per animal killed (this was later increased to 2 cents by the end of 1902 and 4 cents by 1904).

Third Pandemic
Depiction of the Third Pandemic

Despite the unpleasantness and difficulty of the job, the hunters almost immediately proved their lethality to the rodent population. The numbers are staggering.

In the first week of the program, April 26 – May 1, the hunters killed 7,985 rats. As the hunters grew more experienced and perfected their techniques, this number rose to over 4,000 per day just over two weeks later. From there, the increase was exponential. On May 30, the hunters killed a total of 15,041 rodents. For most of June, the number of rats destroyed reached at least 10,000 a day. Peak rodent-mortality was achieved on June 12, when 20,114 rats met their end. This was almost matched by the death-count of July 4.

However, despite the tens of thousands of rats that had been destroyed, the hunters’ efforts appeared to have had no noticeable effect on the rodent population. Indeed, scientific rat population modelling reveals that the hunters’ operations had barely made a dent. The creatures were simply breeding way too quickly.

In desperation, the government, in the colourful words of Vann, ‘added vigilantes to its team of professional killers.’ A 1 cent bounty was placed upon each rat. Anyone could claim the reward. All they had to do was present the rat tail to the authorities.

Within days, there was a veritable flood of Vietnamese handing in rat tails. Government officials were delighted. This was the kind of scale they needed to effectively combat the rat pandemic.

Eventually, however, some disturbing reports began to filter in. Tail-less rats began appearing throughout the city. Upon further investigation, it seemed that some particularly cunning Vietnamese had begun catching rats, cutting their tails off so as to claim the reward and then releasing them back into the sewer system to continue to breed more rats.

Later, health officials made an even more alarming discovery. In some sheds on the outskirts of the city, some particularly entrepreneurial Vietnamese had set up some rat breeding operations, raising the very rodents they were supposed to be hunting in order to claim the bounty.

In the face of such fraudulent schemes, the government had little choice but to scrap the bounty. For the rat-breeders, their rodent cash-cows were suddenly worth very little at all. Perhaps unsurprisingly, the breeders responded by simply releasing the captive rats into the wild. In a stroke, the rodent population grew by thousands and the problem became far worse than it had been at the start. In the French colonial government v Rattus norvegicus, the rodent had emerged victorious.

The Great Hanoi Rat Hunt is a prime example of what is known as the Cobra Effect, which is when the proposed solution to a problem leads to perverse outcomes and ultimately ends up making the problem worse. The name is derived from an almost identical case in British India, with cobras in place of rats. However, Vann points out that, since there is no actual evidence of the cobra incident, it should really be called the Rat Effect.

To this day, rats are an everyday part of life in Hanoi and despite an estimated 55 million rodents killed each year, they ain’t going away any time soon.


  • Vann, Michael G. “Of Rats, Rice, and Race: The Great Hanoi Rat Massacre, an Episode in French Colonial History.” French Colonial History, Vol. 4 (2003), pp. 191-203.
  • Logan, William Stewart. Hanoi, Biography of a City, Seattle, WA: University of Washington Press, 2000.
  • Vann, Michael G: The Great Hanoi Rat Hunt: Empire, Disease And Modernity In French Colonial Vietnam, Oxford University Press, 2018.

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