Governments around the world are struggling with a problem. Well, piles of problems actually, but one specific problem countries that have been hit hard by COVID-19 (and perhaps don't have the strongest sick pay laws) are struggling with is getting people to self-isolate for the required number of days when they or someone they've come into contact with contracts the disease.

In the UK, an idea has been floated by the government to tackle the issue: pay £500 to anyone who tests positive for the virus. Aimed at supporting people who may not be able to afford to not go to work, critics have suggested it could backfire by effectively incentivizing catching a deadly disease.

It's been likened quite a bit on Twitter (in hyperbolic terms) to saying "get yourself infected and we'll treat you to a PS5 and a holiday".

While the vast, vast majority of people will of course not do this (if any at all), it's a fun opportunity to look back at a time when an incentive backfired spectacularly. We give you: the great rat massacre of 1902.

In Hanoi, Vietnam, rats were a huge problem around the turn of the 20th century. Or more specifically, they had long been a problem, but now the colonial French viewed them as a problem too after Alexandre Yersin discovered the bacillus bacteria responsible for the bubonic plague, and the role that rats and fleas played in spreading it. 

Rats would occasionally use the pipes that served the flushing toilets of the colonialists (unavailable to the local population) as an entry point into their homes. Suddenly the pests, largely kept away from the colonialists' spacious mansions and confined to the poorer Vietnamese areas of Hanoi, moved from being "no biggie" to "they must be destroyed this instant" (see also: the UK government didn't deal with cholera until the smell from the river Thames started ponging up Parliament).

Worried about the plague, the French got stuck in and tried to deal with the problems themselves. Only kidding, they hired locals to go down into the cramped, dank sewers in order to kill the potentially disease-filled rats below. In the first week of the project, the rat-killing team managed to kill 7,985 rats. As their killing techniques improved (sadly we have no records of how they improved) they managed to kill 20,114 rats in a single day. 

"It is hard to imagine a more incongruous image than that of the colonial civil servant, dressed in white from head to toe and on his way home to his spacious villa, coming into contact with a native sewer worker, covered in filth and carrying hundreds of bloody rat corpses," historian Michael G. Vann wrote in a paper on the topic.

Despite the slaughter, it soon became apparent that they weren't even putting a tiny dent in the rat population. The colonial administration, like Californian recruiting kids as squirrel killers in 1918, decided to turn to amateur vigilantes rather than paid professionals.

The administration began paying members of the public to kill rats, or so they thought. Deciding that it would be too much of an effort to deal in rat corpses, the colonial rulers decided that they would pay 1 cent per rat tail. 

At first, the scheme looked like a massive success. Rat tails were flooding in, and it appeared people were slaughtering the rodents in impressive numbers.

Soon though, officials venturing into the Vietnamese part of the city took a closer look at some of the rats running around and noticed a distinct lack of tail where the tail should be. Rather than killing the rats, entrepreneurial types had merely cut off their tails and released them into the wild to breed more valuable tails. 

Essentially, in an attempt to incentivize rat-killing, the government had accidentally incentivized rat maiming. Worse, people started farming the rats themselves in order to make money. The rat population exploded, and a year later the city began to see cases of bubonic plague, followed by a larger outbreak in 1906. 

So, back to COVID-19 and what we can learn from a rat massacre. When tackling a disease there are certain goals you will need to achieve (currently it's getting people to stay at home, in 1902 it was slaughtering hundreds of thousands of rats), but how you go about it is important. Incentivize in the wrong way, and you might just find (in a tiny, tiny minority of people) that you're incentivizing some other behavior entirely.

[H/T: Twitter/cheianov]