In rural Arizona we deal with pack rats [0]. These are sometimes-destructive nuisances. For example, my father replaced his car's spark plug wires. The new wires rapidly disappeared - apparently rodents need to chew hard things to keep their teeth from getting too long. Father bought a second set of wires from the same company, which again rapidly disappeared. Apparently some kinds of spark plug wires are coated with rodent bait (peanut oil?). The third set of wires was from a different company. These did not have rat bait like the other company's wires.
My neighbor leaves their vehicle hoods open while on their rafting trips... he also uses live traps to catch and relocate the rats around his house. Otherwise pack rats will set up a nest in vehicles' engine area, destroying the wires and filling it with twigs and food.
An Arizona company [1] came up with a sort of poison that only targets rodents' reproductive organs: "ContraPest contains the ovotoxic chemical 4-vinylcyclohexene diepoxide (VCD), which is a known killer of oocytes in immature ovarian follicles. The rat version of ContraPest also contains triptolide, which the company reports has adverse reproductive effects on both males and females. The product has been successfully used to sterilize both male and female mice, rats, and dogs." [2]
As "Mr. Pack Rat" explains, it's better to understand the pack rat than to indiscriminately poison them, as rodent predators fall victim to secondary poisoning with standard city-rat poisons, which makes pack rat problem worse [3].
Oh gosh, packrats are such a PIA. They seem to love garages when they can get in -- I guess no snakes, no birds of prey, no bobcats, etc. And this thing about chewing wires in cars.
I don’t know if most rats enter the home through the front door. I would guess that is pretty rare. Unsealed crawl spaces and attics are much more likely to be the culprit.
Even then, they don’t necessarily do any harm. As long as the interior of the home is sealed, they can’t get in. Our building definitely has rats, and we saw one in our home shortly after we rented it. The previous tenants had just trapped rats they saw, but we insisted that the landlord send someone to seal every ingress point (with copper wool and silicone gel). Since then we haven’t had an issue, even though our little visitor would come daily before.
As a bonus, the same way rats get in, so do cockroaches. In NYC, older buildings, especially near the ground floor, are notorious for cockroach infestations. But we don’t have any of those in our unit either, despite the building being a century old. Turns out cockroaches and rats aren’t made of magic. They can’t teleport through solid material. If the interior of your home is sealed, they cannot get in.
Front door, back door, side door, whatever. Our backyard abuts undeveloped easements in San Francisco and we see rats out at evening and night. I've literally closed the door on a rat trying to tailgate after me. Door was only open long enough for me to walk through.
Roaches have more entry points since they can fly and scale vertical walls.
See How Easily a Rat Can Wriggle Up Your Toilet | National Geographic https://www.youtube.com/watch?v=0t2VPBF6Kp4 - Also as the owner of three pet rats, can confirm they can get through the most ridiculously small holes.
I've found rats living inside the CNC machines at my work. Under the rail covers at the very front just past the sensor that stops the machine from travelling further. There's a tiny hole underneath the rails that would have been the only way in. I also found them living inside another machine at work. The only way to access where they were living in that one would have been to crawl up the drain pipe and squeeze under the tiny gap between the cover. I also found one dead between two slabs of stone. No idea how it got there
My house however lacks rats. We've had an ongoing competition between the two cats. They're pretty evenly matched at this point for rats and mice caught.
I believe that rats have come up toilets non-zero times in history, but it’s never happened to me, nor did anyone I told about our rat problem mention it having happened to them.
Rats can definitely squeeze into very small spaces. However, they cannot squeeze through packed copper wool impregnated with silicone caulk.
My feeling is rats avoid places with an active human presence. And they also avoid spaces occupied by cats.
They are basically everywhere people are. Friend has a house in a Suburban neighborhood. Along one side of his property is a long dense hedge. It's a rat superhighway.
I know rats can chew through many things. I did not know about cement. Fortunately, houses are not made of cement. They are made of concrete. And, as far as I can read online, only improperly cured concrete is vulnerable to rats. Rats also cannot chew through copper.
There’s also a question of how thick the material, and how motivated the rat. Can rats make a dent in bricks? Yes. Is a single rat going to chew a hole all the way through a brick wall just to see that’s on the other side? I’m no rodent behavior expert, but I doubt it.
More to the point (at least according to YouTube exterminators) rats will only chew through things if they have a reason to. That is why you seal holes with silicone caulk after the copper wool: to prevent the smell of food from drawing rats in.
In any case, I can only tell you what treatment we applied and what the results were. There is a lot of information on the internet about how to prevent rat ingress in apartments and buildings. Based on my experience, that information seems accurate. But another approach is to assume nothing can be done and live with periodic rat infestations.
Certainly it seems like total eradication is the best option. The article just posits that one-off killings have a negative effect.
Knowing that the partial killing of a rat "family" potentially increases the diversity and potency of bacteria seems like very useful information in a world where we can't easily kill all rats.
Near the end of the article it mentions that existing rat populations act as a buffer against invasive species carrying new infections. This is pretty important for port cities, probably less so for inland areas.
I'm surprised they didn't mention it in the article, but Alberta (a province adjacent to British Columbia on the east side) is mostly rat-free (infestations per year at 0 or in the low single digits since 2000. It is entirely land-locked though. As far as I know there have been no adverse effects. They started aggressive rat control in the '50s.
My neighbor leaves their vehicle hoods open while on their rafting trips... he also uses live traps to catch and relocate the rats around his house. Otherwise pack rats will set up a nest in vehicles' engine area, destroying the wires and filling it with twigs and food.
An Arizona company [1] came up with a sort of poison that only targets rodents' reproductive organs: "ContraPest contains the ovotoxic chemical 4-vinylcyclohexene diepoxide (VCD), which is a known killer of oocytes in immature ovarian follicles. The rat version of ContraPest also contains triptolide, which the company reports has adverse reproductive effects on both males and females. The product has been successfully used to sterilize both male and female mice, rats, and dogs." [2]
As "Mr. Pack Rat" explains, it's better to understand the pack rat than to indiscriminately poison them, as rodent predators fall victim to secondary poisoning with standard city-rat poisons, which makes pack rat problem worse [3].
[0] https://www.mrpackrat.net/packrats.html#six
[1] https://senestech.com
[2] https://en.m.wikipedia.org/wiki/ContraPest
[3] https://www.mrpackrat.net/poison.html#fou