This was used in one of the Discword novels (Soul Music):
Shortly before the Patrician came to power there was a terrible plague of rats. The city council countered it by offering twenty pence for every rat tail. This did, for a week or two, reduce the number of rats—and then people were suddenly queueing up with tails, the city treasury was being drained, and no one seemed to be doing much work. And there still seemed to be a lot of rats around. Lord Vetinari had listened carefully while the problem was explained, and had solved the thing with one memorable phrase which said a lot about him, about the folly of bounty offers, and about the natural instinct of Ankh-Morporkians in any situation involving money: “Tax the rat farms.”
That last line might actually lead to the solution. Have a rat tax levied on land owners, in proportion to their alottment of land, and how many rats government officials find in the district where the respective land holdings are situated, and empower land owners to appoint whichever rat exterminator that they like for their district. I imagine that will lead to the incentives needed to solve the problem.
I can only see the image of a man they call Cat Driver, the bane of rats. His pack of ferocious felines, about three score, their leashes bound in his callous hands, trained in the deadly art of Ea'tin A'Ra-t, they track and murder every poor beady-eyed non-soul unfortunate enough to be within a league of a nose.
Then when we're overrun by the cats, we'll unleash wave after wave of Chinese needle snakes to keep their population in check. Then when we're overrun by snakes, we have a fabulous type of gorilla that thrives on snake meat.
Fun fact, professional rat hunters tend to prefer Dachshunds over cats; they’re easier to train and will hunt on command rather than whim. It’s no good to bring cats only to watch them start murdering pigeons, or take a nap.
The legend dates back to the Middle Ages, the earliest references describing a piper, dressed in multicolored ("pied") clothing, who was a rat-catcher hired by the town to lure rats away with his magic pipe. When the citizens refuse to pay for this service as promised, he retaliates by using his instrument's magical power on their children, leading them away as he had the rats.
I assume you mean this rat tax would be instead of the rat bounty. If that is the case, then I agree it would probably be a better solution than the rat bounty.
But, as long as we are exploring alternate solutions to the original problem, my feeling is that it would be better overall to spend more on garbage collection and street cleaning.
The same happened in Rio de Janeiro in a campaign against bubonic plague in 1904. This is whats happen when you try to make a duct tape fix for a huge inequality problem.
> Since anyone could sell rats to the government, a new occupation soon appeared in the city: “ratoeiros”—literally, ratters—men who went around town buying up rats at a low price and selling them to the General Directorate of Public Health. There were even some who raised rats at home for this very purpose and also those who traveled to other cities to find them. In a short while, the “ratter” trade was doing a booming business.
This reminds me of the attempt to control sparrow populations during China's Great Leap Forward. Chinese scientists had determined that sparrows were eating too much of farmers crops and decided to launch a nation-wide campaign where everyone was encouraged to kill sparrows by any means necessary. Unlike this article however, the extermination of sparrows (and other birds) was incredibly effective. Unfortunately, this lead to the proliferation of insects such as locusts which ironically (and tragically) caused more damage to crops than sparrows ever could and contributed to a famine which killed millions
We have something of a mouse plague here in rural New South Wales (Australia) at the moment.[1]
Such measures wouldn't even begin to put a dent in numbers here.
Right now they're trying to fast-track approval of some quite strong pesticides in an effort to control it, but some are worried about the collateral damage.[2]
Although a much smaller feat, New Zealand was very successful in eradicating an estimated 200.000 mice from Antipodes Island without affecting native animals populations [1]
There is an interesting video about the preparatory research leading up to this highly successful pest eradication [2]
Very curious to see how well the Predator Free 2050 program will turn out.
We do often see a cyclical rise in the populations of rats, however a population increase of this size has never been recorded before. It is currently 400% of the size of the last record holder, and still growing.
My father in law told me of a gopher bounty in Ticino that went exactly twice as well as planned: the Ticinese communes paid 10 cents a tail. The only problem was that in nearby Grisons, the government was paying 10 cents per head...
> So what does he think the lesson is instead? “To watch out for programs being created in situations where where the arrogance is so strong and the power differential is so intense that evidence can be ignored.”
Like stack ranked performance reviews, and arbitrary firing targets.
>the power differential is so intense that evidence can be ignored
This is a good point from the article to expand on, it's not just coincidence that the Hanoi rat massacre and the Delhi cobra hunt both feature colonial governments.
That quote applies to just about every example given on the perverse incentive Wikipedia page.
Or, despite the assurance that using it as an "argument against government intervention of any kind… misses the point," almost any situation where government is involved. Because especially national government solutions have by nature an extreme power differential, are almost always conceived in the arrogance of unchallenged authority, and affect such complex systems, they almost invariably create a wide array of perverse incentives.
Even if they had managed to kill an even larger number of rats at once, in one shot. I wonder how much progress they'd make.
Rats have very short lifespans and breed quickly. As it is there's a lot of rat turnover. I suspect that just with mass extermination it would be pretty hard to control the population.
I can't speak to rats specifically, but in my state feral hogs are a problem. The state wildlife office doesn't let hunters take them on public land, because it makes them skittish and they stay spread out (you can take them on private land with a landowner's okay, though).
They set up baited traps where a giant cage is suspended, which then falls onto the whole...team. (I looked up the word for a group of hogs)
Anyway the relevant bit is that supposedly, each year you have to kill/remove 60% of the existing hogs just to maintain the current population
My superficial googling suggests pig and hog were once, like piglet, developmental subcategories of swine (unweaned and ready-for-market). Like shoat (weaned), and gilt/sow (female that hasn't/has reproduced). But meaning has blurred and diversified since.
> They set up baited traps where a giant cage is suspended, which then falls onto the whole...team
Have you seen this? Normally the gate drops only. Many ways but what seems normal in my experience, guys set up a trap with multiple entry/exists with food inside. Over time they reduce to one entry with a gate that has a trip wire or more commonly these days a camera with remote control gate release. Sometimes people use wire mesh panels overlapping to create a gate that pigs can push through one way only too.
We just had a massive boom where I am. Pigs foraging within 10m of the house (normally they would never be within 100m) and moving further into our valley than we'd ever seen before.
A sibling comment to yours included a link to a youtube video demonstrating exactly what I was talking about. They talk pretty extensively about different types of traps and their effectiveness during what seems like fairly extensive research.
There's some Plans around where they introduce mutations into the gene pool of a plague (I know they did it with mosquitoes, but possibly rats and mice as well). I believe it's something like a recessive gene that causes infertility after a few generations?
That's a gene drive[0], and it violates the normal pattern of inheritance by ensuring that even if an organism only inherits the variant allele from one parent, it is guaranteed to pass it on to all of its offspring.
Quite a lot of land in Hanoi is dedicated to agriculture. Even Hong Kong has some farmland, for that matter.
According to one paper, about two decades ago, half of Hanoi province’s land was used for agriculture.¹ I don’t know the relation between the province and the city area. However, at table 4 there are supposedly 0.25 ha of agricultural land per household in the City Districts—more than in certain other areas in Hanoi province! A decline in the proportion of land dedicated to agriculture is likely to have occurred. But urban agriculture does not seem to have been eliminated. According to another (2010) article, the local government considers the growing of ‘modern’ vegetables (instead of less appealing rice—I don’t really understand this æsthetic preference) an important priority in preventing the city from looking outdated.² A reasonable number of farmers are interviewed. This suggests that a good number of urban farmers remained at least then. The most recent article I can find is from 2019, when the Asia Foundation published a post on their blog about a programme to assist local farmers.³
It’s very easy I think to forget that agriculture isn’t entirely squeezed out of highly urbanised Asian cities.I only realised recently that there were farms in Singapore: my relatives never mentioned them, even though they are always very eager to show me other parts of the city—possibly because they don’t know about them.
Returning to the original article, then, crops probably do pose a problem in controlling rat populations.
AIs are the best at exploting unexpected perverse incentives.
You will see this whenever you train an AI to play a video game. It will eventually find a glitch and exploit it endlessly in the weirdest of ways.
If you poorly design an AI to lower crime rate in a given population, it can come up with a solution where population = 0 and therefore crime rate is 0.
> If you poorly design an AI to lower crime rate in a given population, it can come up with a solution where population = 0 and therefore crime rate is 0.
Isn’t that kinda the plot to the movie iRobot? And/Or terminator?
> If you poorly design an AI to lower crime rate in a given population, it can come up with a solution where population = 0 and therefore crime rate is 0.
Since crime rates are in offenses per capita, the crime rate would actually be undefined in that case.
The mistake would setting a fixed population denominator, not accounting for deaths and demise. This would be a disconnect that would allow the rate to be defined.
This poorly designed AI you speak of is the premise of I, Robot by Asimov. In fact, this is one of the fears surrounding AGI - the AGI would be correctly configured to act only for the benefit of humanity, however, in typical AI fashion, this leads to unexpected (and often undesirable) effects.
The turning in tails of pests for a small fee, was quite common at the time around the world.
When researching my g-great grandfather, the county (PA, USA) he lived in still had records of each time he turned in a fox's tail in their Noxious Animal Docket from 1908.
For the most part, they don't. Virtually all sever systems are populated by rats. Watch any manhole during a hot summer's day from afar, and you won't have to wait long to see a rat.
Some factors like average flow speed and more slippery pipes, toilet cleaning chemicals, but also changes in how sewers are used (e.g. no longer for food waste disposal) have lowered rat population sizes - and Hanoi being a tropical city probably had some effects as well.
I am not an expert, but when I think of "old fashioned" sewers, I think of the vaults with a 'river' running, with footpaths on both sides - you know, the type from video games and movies. The sewers here are just pipes though, no room for people to walk through, no access points, no direct openings into a public waterway, and constant one-way flow. I'm not sure if they continuously run water through it, but I can imagine they would.
you definitely don't want a sewer system that is only pipes, open channel flow is essential to ensure that sewage doesn't become pressurized, unless you want exciting effects like toilet fountains.
Basically every sewer system has video game style free flowing open air vaulted areas, although usually at smaller scale.
There was an article here on HN that a stable rat population is probably better than unsuccessful attempts at control. The reasoning was that rats live in groups which are territorial, so normally keep their distance, which limits the spread of diseases.
Killing rats makes the groups flee their territories, which breaks this mechanism and thus helps pathogens spread.
Cats aren't effective at controlling rat populations, and they kill many birds and small animals that already have a hard time surviving in reasonable numbers.
You can see with your own eyes in Israel that this doesn't really work. Though i wonder how many more rats there would be without them. Similar in UK with the foxes.
> “It’s sort of a morality tale for the arrogance of modernity, that we put so much faith into science and reason and using industry to solve every problem,” Vann says [...] So what does he think the lesson is instead? “To watch out for programs being created in situations where where the arrogance is so strong and the power differential is so intense that evidence can be ignored.”
These statements feel so ridiculous in this context. So instead of science, reason, and industry what should we use to control rat population? Faith and prayers? Homeopathy and energy crystals? And how exactly were French ignoring evidence? To me it seems they were perceptive of the evidence, tweaking the program as they went and finally terminating it. And how did power differential come into play here at all?
This was used in one of the Discword novels (Soul Music):
Shortly before the Patrician came to power there was a terrible plague of rats. The city council countered it by offering twenty pence for every rat tail. This did, for a week or two, reduce the number of rats—and then people were suddenly queueing up with tails, the city treasury was being drained, and no one seemed to be doing much work. And there still seemed to be a lot of rats around. Lord Vetinari had listened carefully while the problem was explained, and had solved the thing with one memorable phrase which said a lot about him, about the folly of bounty offers, and about the natural instinct of Ankh-Morporkians in any situation involving money: “Tax the rat farms.”
That last line might actually lead to the solution. Have a rat tax levied on land owners, in proportion to their alottment of land, and how many rats government officials find in the district where the respective land holdings are situated, and empower land owners to appoint whichever rat exterminator that they like for their district. I imagine that will lead to the incentives needed to solve the problem.
It might also lead to significant poisoning/extermination of wildlife other than rats. (Feral cats are cheap and “all natural” for example.)
I can only see the image of a man they call Cat Driver, the bane of rats. His pack of ferocious felines, about three score, their leashes bound in his callous hands, trained in the deadly art of Ea'tin A'Ra-t, they track and murder every poor beady-eyed non-soul unfortunate enough to be within a league of a nose.
Then when we're overrun by the cats, we'll unleash wave after wave of Chinese needle snakes to keep their population in check. Then when we're overrun by snakes, we have a fabulous type of gorilla that thrives on snake meat.
https://youtu.be/3f5viRoaZNw?t=89
Fun fact, professional rat hunters tend to prefer Dachshunds over cats; they’re easier to train and will hunt on command rather than whim. It’s no good to bring cats only to watch them start murdering pigeons, or take a nap.
Dachshunds over terriers?
Dachshunds were bred to get into burrows, hence the sausage shape.
'Dachshund' literally translates to badger-hound; they're bred to go down burrows and drive out badgers.
Just use a magic pipe.
https://en.wikipedia.org/wiki/Pied_Piper_of_Hamelin:
The legend dates back to the Middle Ages, the earliest references describing a piper, dressed in multicolored ("pied") clothing, who was a rat-catcher hired by the town to lure rats away with his magic pipe. When the citizens refuse to pay for this service as promised, he retaliates by using his instrument's magical power on their children, leading them away as he had the rats.
I assume you mean this rat tax would be instead of the rat bounty. If that is the case, then I agree it would probably be a better solution than the rat bounty.
But, as long as we are exploring alternate solutions to the original problem, my feeling is that it would be better overall to spend more on garbage collection and street cleaning.
The same happened in Rio de Janeiro in a campaign against bubonic plague in 1904. This is whats happen when you try to make a duct tape fix for a huge inequality problem.
Reference: http://oswaldocruz.fiocruz.br/index.php/en/biography/scienti...
> Since anyone could sell rats to the government, a new occupation soon appeared in the city: “ratoeiros”—literally, ratters—men who went around town buying up rats at a low price and selling them to the General Directorate of Public Health. There were even some who raised rats at home for this very purpose and also those who traveled to other cities to find them. In a short while, the “ratter” trade was doing a booming business.
This reminds me of the attempt to control sparrow populations during China's Great Leap Forward. Chinese scientists had determined that sparrows were eating too much of farmers crops and decided to launch a nation-wide campaign where everyone was encouraged to kill sparrows by any means necessary. Unlike this article however, the extermination of sparrows (and other birds) was incredibly effective. Unfortunately, this lead to the proliferation of insects such as locusts which ironically (and tragically) caused more damage to crops than sparrows ever could and contributed to a famine which killed millions
Sparrows were not the only target for eradication at that time: https://en.wikipedia.org/wiki/Four_Pests_campaign
The article mentions the "cobra effect", which is basically the same story, only set in India with the British offering bounties for dead cobras:
https://en.wikipedia.org/wiki/Perverse_incentive#The_origina...
We have something of a mouse plague here in rural New South Wales (Australia) at the moment.[1]
Such measures wouldn't even begin to put a dent in numbers here.
Right now they're trying to fast-track approval of some quite strong pesticides in an effort to control it, but some are worried about the collateral damage.[2]
Warning: Many pictures of mice dead and alive.
[1] https://www.abc.net.au/news/2021-05-11/farmers-step-up-battl...
[2] https://www.abc.net.au/news/2021-05-24/nsw-mouse-plague-farm...
New Zealand has a "Predator Free 2050" program to eliminate all non-native predators by 2050 because they are threatening New Zealand's bird species.
https://en.wikipedia.org/wiki/Predator_Free_2050
https://www.bbc.com/news/world-asia-48702762
Well this has a non-zero chance of turning into "Unchecked prey 2050" in reality.
The program is specifically about non-native predators, not all predators.
You're assuming NZ has significant native predators. But it doesn't have any major native mammalian predator.
https://www.nznatureguy.com/2019/04/10/new-zealands-big-3-pr...
One interesting "proof" of it is the Kiwi bird existing, because it could have not existed with competent predators.
If you don't have a native predator then you don't have a native prey either. Need a predator for there to be a prey.
Although a much smaller feat, New Zealand was very successful in eradicating an estimated 200.000 mice from Antipodes Island without affecting native animals populations [1]
There is an interesting video about the preparatory research leading up to this highly successful pest eradication [2]
Very curious to see how well the Predator Free 2050 program will turn out.
[1] https://www.doc.govt.nz/our-work/eradicating-mice-from-antip...
[2] https://www.youtube.com/watch?v=gVcqLblOHCM
Will be interesting to see how well this works given the political impossibility of eradicating cats.
Is this a cyclical event brought on by a natural phenomenon like mautam, the rat flood?
[0]https://en.wikipedia.org/wiki/Mautam
Yes and no.
We do often see a cyclical rise in the populations of rats, however a population increase of this size has never been recorded before. It is currently 400% of the size of the last record holder, and still growing.
Another former French colony still has a rat (well, beaver sized rat) bounty-- Louisiana's $6/tail Nutria bounty!
https://www.nola.com/news/environment/article_a5b2f5f6-99f4-...
My father in law told me of a gopher bounty in Ticino that went exactly twice as well as planned: the Ticinese communes paid 10 cents a tail. The only problem was that in nearby Grisons, the government was paying 10 cents per head...
> So what does he think the lesson is instead? “To watch out for programs being created in situations where where the arrogance is so strong and the power differential is so intense that evidence can be ignored.”
Like stack ranked performance reviews, and arbitrary firing targets.
>the power differential is so intense that evidence can be ignored
This is a good point from the article to expand on, it's not just coincidence that the Hanoi rat massacre and the Delhi cobra hunt both feature colonial governments.
That quote applies to just about every example given on the perverse incentive Wikipedia page.
A government need not be colonial to be aloof.
Well of course not, but it's a pretty strong risk factor.
Or, despite the assurance that using it as an "argument against government intervention of any kind… misses the point," almost any situation where government is involved. Because especially national government solutions have by nature an extreme power differential, are almost always conceived in the arrogance of unchallenged authority, and affect such complex systems, they almost invariably create a wide array of perverse incentives.
Even if they had managed to kill an even larger number of rats at once, in one shot. I wonder how much progress they'd make.
Rats have very short lifespans and breed quickly. As it is there's a lot of rat turnover. I suspect that just with mass extermination it would be pretty hard to control the population.
I can't speak to rats specifically, but in my state feral hogs are a problem. The state wildlife office doesn't let hunters take them on public land, because it makes them skittish and they stay spread out (you can take them on private land with a landowner's okay, though).
They set up baited traps where a giant cage is suspended, which then falls onto the whole...team. (I looked up the word for a group of hogs)
Anyway the relevant bit is that supposedly, each year you have to kill/remove 60% of the existing hogs just to maintain the current population
Needless to say, doesn't seem like it's working.
[adds "team" to vocabulary as the term of venary for hogs] Thanks!
You'll be interested to know there were several related words, I just chose one:
Group of pigs: drift or drove
Group of hogs: tassel or team
Group of "swine" (? I don't know the difference): sounder
Piglets: farrow or litter or squeal
Illinois says: herd
>Group of "swine"
Legislature
> (? I don't know the difference)
My superficial googling suggests pig and hog were once, like piglet, developmental subcategories of swine (unweaned and ready-for-market). Like shoat (weaned), and gilt/sow (female that hasn't/has reproduced). But meaning has blurred and diversified since.
I thought it was "sounder"
> They set up baited traps where a giant cage is suspended, which then falls onto the whole...team.
For an example and further explanation: https://youtu.be/rsFXhGoDnW0
Notably they speak of needing to trap >70% of the population just to keep it stable
I laughed out loud at the cows in the conventional trap.
Grew up in a rural area, feels like a very typical 'silly' cow type thing.
> They set up baited traps where a giant cage is suspended, which then falls onto the whole...team
Have you seen this? Normally the gate drops only. Many ways but what seems normal in my experience, guys set up a trap with multiple entry/exists with food inside. Over time they reduce to one entry with a gate that has a trip wire or more commonly these days a camera with remote control gate release. Sometimes people use wire mesh panels overlapping to create a gate that pigs can push through one way only too.
We just had a massive boom where I am. Pigs foraging within 10m of the house (normally they would never be within 100m) and moving further into our valley than we'd ever seen before.
A sibling comment to yours included a link to a youtube video demonstrating exactly what I was talking about. They talk pretty extensively about different types of traps and their effectiveness during what seems like fairly extensive research.
Thanks, hadn't see that.
There's some Plans around where they introduce mutations into the gene pool of a plague (I know they did it with mosquitoes, but possibly rats and mice as well). I believe it's something like a recessive gene that causes infertility after a few generations?
That's a gene drive[0], and it violates the normal pattern of inheritance by ensuring that even if an organism only inherits the variant allele from one parent, it is guaranteed to pass it on to all of its offspring.
[0] https://en.wikipedia.org/wiki/Gene_drive
What would be the modern approach to solving the same problem?
Proper environmental hygiene:
- No hole for them to sneak into kitchens, etc
- No food left around for them to eat
- No place for them to hide and breed
That, and maybe rat-killing robots, equipped with computer vision, who won't cheat on you.
With them eating crops, it might be difficult to achieve 'no food left around for them to eat'
There presumably aren't very many crops in Hanoi.
Quite a lot of land in Hanoi is dedicated to agriculture. Even Hong Kong has some farmland, for that matter.
According to one paper, about two decades ago, half of Hanoi province’s land was used for agriculture.¹ I don’t know the relation between the province and the city area. However, at table 4 there are supposedly 0.25 ha of agricultural land per household in the City Districts—more than in certain other areas in Hanoi province! A decline in the proportion of land dedicated to agriculture is likely to have occurred. But urban agriculture does not seem to have been eliminated. According to another (2010) article, the local government considers the growing of ‘modern’ vegetables (instead of less appealing rice—I don’t really understand this æsthetic preference) an important priority in preventing the city from looking outdated.² A reasonable number of farmers are interviewed. This suggests that a good number of urban farmers remained at least then. The most recent article I can find is from 2019, when the Asia Foundation published a post on their blog about a programme to assist local farmers.³
It’s very easy I think to forget that agriculture isn’t entirely squeezed out of highly urbanised Asian cities.I only realised recently that there were farms in Singapore: my relatives never mentioned them, even though they are always very eager to show me other parts of the city—possibly because they don’t know about them.
Returning to the original article, then, crops probably do pose a problem in controlling rat populations.
1: https://journals.sagepub.com/doi/pdf/10.1177/095624780301500...
2: https://journals.openedition.org/factsreports/464
3: https://asiafoundation.org/2019/07/17/going-green-urban-farm...
Huh. Well, learned something today; I'd never even have imagined this, particularly about Singapore!
Aside from robotic death machines these are all preventative. Which is of course better, but only works if you aren't currently suffering.
Is there a modern solution to "my city is full of plague rats right now" other than evacuate?
The Alberta government started a rat free program in the 1950s. This article is fairly comprehensive:
https://www.alberta.ca/history-of-rat-control-in-alberta.asp...
Municipal water sanitation
Fine for rat infested houses
Significant Fines and inspection for business especially live markets, food factories and mills
Citizen education program, such as encouraging cats, not leaving food around, inspecting homes for holes
Strict garbage collection. Fines for properties that leave garbage outdoors outside garbage collection days
AIs are the best at exploting unexpected perverse incentives.
You will see this whenever you train an AI to play a video game. It will eventually find a glitch and exploit it endlessly in the weirdest of ways.
If you poorly design an AI to lower crime rate in a given population, it can come up with a solution where population = 0 and therefore crime rate is 0.
> If you poorly design an AI to lower crime rate in a given population, it can come up with a solution where population = 0 and therefore crime rate is 0.
Isn’t that kinda the plot to the movie iRobot? And/Or terminator?
Another famous variation is the paperclip maximizer https://en.wikipedia.org/wiki/Instrumental_convergence#Paper...
And what happens with the computer in "Space Odessey - 2001"
> If you poorly design an AI to lower crime rate in a given population, it can come up with a solution where population = 0 and therefore crime rate is 0.
Since crime rates are in offenses per capita, the crime rate would actually be undefined in that case.
The mistake would setting a fixed population denominator, not accounting for deaths and demise. This would be a disconnect that would allow the rate to be defined.
This poorly designed AI you speak of is the premise of I, Robot by Asimov. In fact, this is one of the fears surrounding AGI - the AGI would be correctly configured to act only for the benefit of humanity, however, in typical AI fashion, this leads to unexpected (and often undesirable) effects.
The turning in tails of pests for a small fee, was quite common at the time around the world.
When researching my g-great grandfather, the county (PA, USA) he lived in still had records of each time he turned in a fox's tail in their Noxious Animal Docket from 1908.
That what is rewarded will be repeated! let that be a life lesson. They should have audited the tails. Always audit, when rats are involved.
The Great Alberta Rat Massacre was a lot more successful. The province claims to have completely got rid of them. [1]
[1] https://www.alberta.ca/history-of-rat-control-in-alberta.asp...
How do modern sewers deal with this?
For the most part, they don't. Virtually all sever systems are populated by rats. Watch any manhole during a hot summer's day from afar, and you won't have to wait long to see a rat.
Some factors like average flow speed and more slippery pipes, toilet cleaning chemicals, but also changes in how sewers are used (e.g. no longer for food waste disposal) have lowered rat population sizes - and Hanoi being a tropical city probably had some effects as well.
I am not an expert, but when I think of "old fashioned" sewers, I think of the vaults with a 'river' running, with footpaths on both sides - you know, the type from video games and movies. The sewers here are just pipes though, no room for people to walk through, no access points, no direct openings into a public waterway, and constant one-way flow. I'm not sure if they continuously run water through it, but I can imagine they would.
you definitely don't want a sewer system that is only pipes, open channel flow is essential to ensure that sewage doesn't become pressurized, unless you want exciting effects like toilet fountains.
Basically every sewer system has video game style free flowing open air vaulted areas, although usually at smaller scale.
There was an article here on HN that a stable rat population is probably better than unsuccessful attempts at control. The reasoning was that rats live in groups which are territorial, so normally keep their distance, which limits the spread of diseases.
Killing rats makes the groups flee their territories, which breaks this mechanism and thus helps pathogens spread.
The British did something almost identical with cobras in Delhi:
https://en.wikipedia.org/wiki/Perverse_incentivea
Perverse Incentives it seems never work
This is a great story about KPIs and incentives gone wrong :)
Great example of 'malicious compliance'.
I have to wonder - why not put screens on drains?
My guess would be that a screen that can stop a rat from going up a toilet, would also prevent other things from going down a toilet
Right, that makes sense. I have a septic tank, and screens are on its output (all liquid).
What’s wrong with biocontrol using cats?
What do cats eat when there are no more rats?
Well feral cats are absolutely horrible for native wildlife, as they don’t just kill the animals you want them to.
I wonder if we can breed, via artificial selection, cats that only hunt rats.
https://www.youtube.com/watch?v=LuiK7jcC1fY
Cats aren't effective at controlling rat populations, and they kill many birds and small animals that already have a hard time surviving in reasonable numbers.
https://www.nytimes.com/2018/10/12/science/cats-v-rats-in-ne...
You want terriers for killing rats, they are absolutely fantastic at it and will kill a stupid number of them quickly since they treat it like sport.
You can see with your own eyes in Israel that this doesn't really work. Though i wonder how many more rats there would be without them. Similar in UK with the foxes.
> “It’s sort of a morality tale for the arrogance of modernity, that we put so much faith into science and reason and using industry to solve every problem,” Vann says [...] So what does he think the lesson is instead? “To watch out for programs being created in situations where where the arrogance is so strong and the power differential is so intense that evidence can be ignored.”
These statements feel so ridiculous in this context. So instead of science, reason, and industry what should we use to control rat population? Faith and prayers? Homeopathy and energy crystals? And how exactly were French ignoring evidence? To me it seems they were perceptive of the evidence, tweaking the program as they went and finally terminating it. And how did power differential come into play here at all?