Hi! It’s Election Day in the United States today. If you haven’t yet voted and you’re eligible to do so, please take the time and cast your ballot! — Dan

The Worst Way to Calm the Rat Population?

Today is Election Day in the United States, and if you’re paying attention to the campaign speeches, rhetoric, and the polls, you probably think there’s nothing — at all — that a clear majority of Americans can agree on. But that’s definitely not true. Here’s an easy one:

Few, if any of us, want rats running around your town unchecked.

And unfortunately, a bad rat control policy can be disastrous.

Efforts to control the rat population aren’t a key issue in the 2024 U.S. Presidential campaign, but that concern has been top of mind in other contexts. In 1855, the bubonic plague began to spread rapidly throughout China, India, and Southeast Asia, claiming the lives of an estimated 15 million people over the course of a century. And the cause of the spread, starting in the late 1800s, was rather well known: rodents. As the CDC explains, “Plague bacteria are most often transmitted by the bite of an infected flea. During plague epizootics, many rodents die, causing hungry fleas to seek other sources of blood. People and animals that visit places where rodents have recently died from plague are at risk of being infected from flea bites.”

In 1882, France took control of what it would call Indochina, but today comprises Cambodia, Laos, and parts of China and Vietnam. France had first-hand knowledge of the dangers of the bubonic plague; the Black Death had struck the nation multiple times in the centuries prior. Sanitation was, therefore, top of mine, and the French governors in Indochina began construction on infrastructure. As the Everything Everywhere podcast explains, “The area where the French colonial administrators lived in Hanoi looked like it could have been in France, minus the climate. The neighborhoods had European houses, wide tree-lined European boulevards, and other European amenities.  The one thing they lacked was flush toilets. Flush toilets would help improve sanitation and bring a modern luxury to the French people of Hanoi. To this effort, they installed 14 kilometers or 9 miles of modern sewer pipes in the French section of the city. These pipes hooked up all of the French homes and allowed them to have modern flush toilets.”

Having a municipal sewer system seems like a good thing — and in most cases it is — but it caused a problem: the rodent population in Hanoi began to explode. Before the sewers were installed, rats scurried about above ground in their search for food. Having a lot of rats running around outside wasn’t great, but at least they remained outside of houses, and, more importantly, the rodents were susceptible to predators that kept the rat population in check. The sewer system created a haven for rats -- they now had a place to roam free, without much risk of being eaten by, say, a cat, and they also could use the pipes to enter people’s homes unperturbed. And that’s exactly what happened. 

In an effort to stop the rats — and to stop the spread of the bubonic plague they were carrying — officials hired rat hunters. But, as Saigoneer explains, this wasn’t very effective: “The government reacted by hiring Vietnamese rat-catching squads. This was horrifying work; catchers were required to climb underground into rivers of human waste to capture disease-ridden rats. During the first week, thousands of rats were killed. At their peak, June 12, the hunters culled 20,114 rodents. Scientific population modeling, however, found these efforts were no match for the rat’s breeding capabilities as a single pair can produce 35-70 offspring a year.” There simply weren’t enough rat-catchers. So authorities decided to enlist everyone to help, by instituting a rat-killing bounty.

This turned out to be a bad idea. 

If you killed a rat, the government would pay you a cent — a decent amount of money for the work, at the time. Officials didn’t want people hauling dead rats into their offices, though, so they told people to just bring in the rats’ tails as proof of a successful kill. The plan seemed to work beautifully, as people from all walks of life began turning in rat tals by the heap. But after a few weeks the rat population didn’t seem to be negatively impacted by the efforts. And then something curious began to happen: there were reports of people seeing tailless rats roaming throughout Hanoi. Some of the people who were turning in rat tails had intentionally let the former owners of those tails survive, in hopes that they would breed more rats, creating more tails, and therefore, more profit for the rat tail collectors.

And they were not alone in this rat-friendly (well, if you don’t mind losing your tail) entrepreneurial endeavor. Per Atlas Obscura, “There were also reports that some Vietnamese were smuggling foreign rats into the city. And then the final straw: Health inspectors discovered, in the countryside on the outskirts of Hanoi, pop-up farming operations dedicated to breeding rats.” The government’s plan to curtail the rat population just led to more rats.

The rat-catching effort, which is now sometimes (but incorrectly?) the Great Hanoi Rat Massacre,” had failed. The bounty system went away almost as quickly as it came to be, and of course, the rat population continued to grow. The plague ultimately ran its course, but not before claiming many more human lives.

More About Rats

Today’s Bonus fact: In the 1960s, the population in poorer communities in Washington, D.C. was out of control, and the local government didn’t seem to be interested in doing anything about it. A man named Julius Hobson helped solve the problem by threatening to make the rats everyone’s problem. WETA explains:

It took a few such threats, but it worked: after a few weeks or months, the government funded rat patrols in the areas in D.C. that actually needed them.

From the Archives: Hero Rats: How rats can save lives (by locating land mines).

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And thanks! — Dan