The place: a modest house at the end of a narrow street in Culver City, Calif. The problem: The house’s owner had been feeding bread to a population of rats, which had moved into her kitchen and living room and then into the ceilings, where they had begun encroaching on the neighboring tenants from above. The diagnosis: “Unbelievable,” said Dave Schuelke, a buff and ruddy-faced exterminator who is one-half of the pest control and home repair company Twin Home Experts. “I’ve never seen this before.”Mr. Schuelke was speaking breathlessly to a camera that he had trained on himself. He was alone behind the house, but his intended audience was the nearly 250,000 subscribers of the Twin Home Experts YouTube channel, where he and his identical twin brother, Jim, post videos of themselves on the job. Nine years ago they began uploading videos about general home repair, with titles like “How to Unclog a Toilet Without a Plunger” and “How to Find a Sewer Odor,” but, more than 70 million views later, their content has skewed toward rats. “Attic Rats! We Smoked Them Out” is one recent title. Also, “Destroying Fat Rats in Washington, D.C.” And “Rat Trapping in Mexico City, We Baited With Churros.”“People want to see that type of gory-looking stuff,” Dave Schuelke said, setting down the camera. “People want to see the action.”View counts are directly related to whether a video’s thumbnail shows some sort of tool — a screwdriver, or a Sawzall, or a bulked-up trap — pointing at a rat. The thumbnail of the Schuelkes’ most popular video, with over five million views, features an airsoft gun pointed at a rat nest.Eric Adams, the mayor of New York City, that ignominious ratropolis, has also been playing on this morbid fascination with the midsize rodents. Since the beginning of his term in 2022, Mayor Adams has been vocal about his fear and hatred of rats and about his drive to kill them. In November, his office posted a job listing for a rat czar; whoever took the job, the listing noted, had to be “somewhat bloodthirsty.” Deployed as a lighthearted rallying point amid other, more charged policies, the anti-rat agenda has been covered extensively by media outlets. “We’re making it clear that rats do not run this city,” Mayor Adams said in a news conference last year.Reasons for controlling the urban rat population are abundant: The animals can spread diseases to humans, destroy property and damage native ecosystems. But rats are also cognitively advanced social animals, and questions about how to effectively control them can raise tricky ethical questions. Glue traps will leave rats starving, for days, before dying. Poison leads to a slow, painful death and can endanger other wildlife. Standard wooden snap traps often catch limbs or tails, forcing rats to gnaw them off in desperation. Live-catch traps are difficult to implement, and when many rats are stuck in the same place together without food, they sometimes eat one another.Even if rats are extracted from an urban environment, what do you do with them? Release them into the woods, where they can damage existing ecosystems? Keep them as pets? Rats are reviled but resilient, dangerous but inculpable. “Right away, you end up in a very uncomfortable position,” said Robert Corrigan, a New York City rodentologist who has studied urban rats for decades. “There’s no way to get out.”Where the Wild Rat Traps AreThe Schuelke brothers, along with a handful of employees, had been moving around the house in Culver City for about three hours, looking for rat nests and openings through which the animals could squeeze. The twins’ strategy was to close off every rat entry and exit point and lay traps around the house as the animals grew hungrier and more desperate.But the whole place was compromised. Holes in the roof, the walls, the floors. The house’s owner, an 82-year-old woman named Ann Chung, said that she could hear rats underneath her at night. She expressed a kind of fondness for the animals — she was feeding them twice a day — and mentioned that, in some countries, there are temples dedicated to rats. (For instance, the Karni Mata Temple in India.) But they were now shredding her collections of newspapers, books and clothes and staining her carpets twice over with urine and grease. “I am defeated in life, in everything now, because of these rats,” Ms. Chung said.There are more than 4,400 mousetrap patents in the United States, but it is difficult to find designs specifically for catching rats — most are just bigger mousetraps. Rat infestations are also often more of an industrial undertaking than mouse infestations are, less of a do-it-yourself project and more of a job for professional exterminators, who are better at reusing traps. Partly because of this, Woodstream, the country’s largest rat and mousetrap manufacturer, sells some 60 million mousetraps a year and nine million rat traps, according to Miguel Nistal, the company’s president and chief executive. Most of these are the classic wooden spring-loaded snap trap, which Woodstream sells under the brand name Victor.Mr. Nistal said that the main complaint he gets about his rat traps is simply that they don’t kill rats. Mice are relatively uncomplicated pests; they go for whatever food source is available and, because they’re small, are easy to dispatch. But Mr. Nistal said that, according to his company’s research, only about 65 percent of the rats that trigger snap traps die. They will wriggle free or outsmart the trap, swiping the bait out safely. Rats are also wary of new things, like traps. “When you and I are gone, and there’s nothing else on earth, there will be roaches and rats,” Mr. Nistal said.Shawn Woods, a YouTuber who reviews mouse and rat traps, said that he often has to leave his rat traps out for a couple of days without setting them so the animals feel safe grabbing the food. Mr. Woods tests a trap every week and has a collection of thousands of rodent traps at his home in Oregon. He began making review videos about six years ago, when his channel had only a handful of subscribers and was focused on primitive survival skills. Then, a video demonstrating an ancient deadfall trap received over a million views.Since then, Mr. Woods has become an influencer in the trapping world, with over 1.7 million subscribers to his channel. New products that he gives positive reviews often sell out on Amazon, and he has met with management at trap manufacturing and design companies, including Woodstream, to share his expertise. Most of the people who reach out to him are amateur inventors who came up with something innovative, like a rat trip wire. “But even if they do have a good idea, actually bringing that to market in a scale where that’s profitable, that’s really difficult,” Mr. Woods said.Mr. Nistal said that he keeps track of “consumer pain points” to help guide further development. Efficacy is one, but other considerations include reusability, keeping the dead animals out of sight, and remote notification that a trap has been activated. To address these needs, Woodstream has developed dozens of traps that fall into three basic categories: glue traps, spring traps and electric traps. Most of the company’s sales, though, come from the classic Victor spring snap trap, which was invented in 1897.That was one of the traps that the Schuelke twins set up in Ms. Chung’s house in Culver City at the end of their first day on the job. The trap was loaded with chunky peanut butter and modified slightly, with a razor blade glued to its edge, to make it, as Dave put it, “the deadliest trap ever.” The other trap was what the Schuelkes called the Twin Ratvac, a vacuum modified to turn on when triggered by the presence of a rat, which would then get sucked into a bucket. Wi-Fi cameras were set up to catch the action. A gust of wind rustled tarps laid out on the back porch. The next step was to wait.“You gotta be a hunter,” said Jim, a smile sneaking onto his face.What Makes a Rat a RatThe primary species of rat in both New York and Los Angeles is Rattus norvegicus, the brown rat: a midsize rodent that has a whiplike tail and is resilient, intuitive and remarkably fecund. (One study found that female brown rats in a Brazilian favela produced 79 viable offspring a year on average.) Brown rats live in colonies and establish networks of tunnels in which they play, groom one another and touch noses in acts of recognition. They also have a large collection of facial expressions and can sense the emotions of others in their colony. Perhaps in part because of this, brown rats have been found to consistently prefer rewards that benefit others, as opposed to just themselves. They can also learn how to drive tiny cars. And dance to Lady Gaga.Much research on rat cognition has focused on lab rats, which are bred for experimentation. But Michael Parsons, an urban ecologist at Fordham University who has spent two decades studying city rats, said that wild brown rats (as well as the smaller and rarer black rats) are even more advanced than their laboratory counterparts. “They have unique personalities, and they experience regret, remorse and social justice,” Dr. Parsons said.Dr. Corrigan, who has lived and slept in barns full of rats to better understand them, concurred: “They’re intelligent animals, they make decisions, they regret when they make decisions, they’re altruistic — everything we have going, they have going.”It can be difficult for scientists like Dr. Parsons and Dr. Corrigan to secure funding for research on wild rats, and even more difficult to attract new researchers. “I think there are fewer than a dozen research teams worldwide that study urban rats,” Dr. Parsons said. This is partly because rats are dangerous — they carry diseases like bubonic plague — and are most populous in environments that most humans don’t enjoy. Brown rats are also known as sewer rats, and can survive on almost any kind of food: fruit, grain, worms, trash, feces, carcasses. Much of Dr. Parsons’s research in New York is carried out in waste management facilities in the dead of night.The argument for researching wild rats often amounts to something like “know thy enemy.” Rats cause an estimated $20 billion in damage annually in the United States alone, gnawing through electrical wires and burrowing into the walls of buildings; they also feast on crops. Jason Munshi-South, a biologist and rat researcher at Fordham University, has written about the evolutionary differences of brown rats worldwide, as well as the genetic variation among rats living in uptown and downtown New York City. Because rats reproduce so prolifically, the invisible hand of natural selection becomes more noticeable. Most city rats have developed immunity to first-generation anticoagulants, rendering many poisons useless.But much less science has been focused on wild rats as rats, rather than as pests. For Dr. Parsons and Dr. Munshi-South, this is a manifestation of society’s bias against the animals. Rats fall into the “special category of things we don’t want to exist,” said Dr. Munshi-South. It’s a self-perpetuating intolerance: The less we know about the animals, the easier it is to hate them, and the easier it is to kill them. “In a way, they are the enemy,” Dr. Parsons said. “But it doesn’t mean we can’t have a heart for them.”Humans vs. Rats vs. HumansRat trappers, and the rat trapping industry, are not unsympathetic to these arguments. Mr. Nistal acknowledged that glue traps are “inhumane,” and he said that his company had been phasing them out. But, he added, for particularly dangerous infestations (for instance, hundreds of rats under a hospital), glue traps are the fastest and most effective method of control.Mr. Woods often considers whether his popularity on YouTube might have less to do with the practical information he imparts and more to do with the spectacle of dead rats. In his videos, he blurs out the rats’ dying moments and often demonstrates traps on stuffed animals, but copycat channels have since popped up that essentially publish rat snuff films. “I have a very fine line to walk, where I’m trying to teach people the best way to control rodents without profiting off of blood and guts and torture,” Mr. Woods said.Some of his videos highlight antique traps, like a 19th-century wooden trap that is shaped like a rat and shoots harpoons from its eyes, or quicksand traps that suffocate rodents. He refuses to feature glue traps and spring traps that aren’t strong enough to immediately kill the rats, which he believes cause unnecessary suffering. Even drowning traps, he found, are morally ambiguous: Some rats can swim for more than a day before succumbing. His favorite setup is the Victor snap trap, modified with wooden blinders so the rats must enter headfirst. His favorite large-scale trap is called the Uhlik Repeater trap, which can catch dozens of live rats in one night. Because brown rats are invasive in Oregon, Mr. Woods then kills them in carbon dioxide chambers, which he thinks is most humane. “For my own conscience, that’s what I do,” he said.Erin Ryan, who works for the British Columbia Society for the Prevention of Cruelty to Animals in Vancouver, Canada, has spent years studying rodent traps and thinking of ways to implement a citywide control program that minimizes harm. “What I’ve learned in my research is that humane means something different to everybody,” she said. “But there’s always a time and place for lethal control when it comes to rodents.” It’s simply unsafe to catch and release hundreds of rats.Ms. Ryan advocates a more holistic approach, starting with an understanding of the animals and their interactions with the urban ecosystem. In the wild, rats face painful deaths at the hands of predators and freezing weather. But in cities, rat issues and rat death almost always can be traced back to people. Humans brought brown rats to North America, destroyed the habitat of potential predators and created environments where rats could thrive. Humans maintain systems of trash and waste and often don’t clean their homes. “City rats are a species that in some sense humans have created,” Dr. Munshi-South said. “They’re evolutionary and ecologically linked to us.”On this, nearly all rat researchers agree. “For me, rats are not the enemy,” Dr. Parsons said. “People are the enemy.”Dr. Corrigan is often hired for massive, complex infestations and designs programs to help control the rodents. He can end up dealing with hundreds of rats living in the walls of a dormitory or in the basements of buildings. When that happens, he said, it’s an “all-out war to eliminate a very real, substantial risk to human health and safety.” But in the end he has to kill animals that he has spent his whole career studying. Years ago, Dr. Corrigan started writing about the contradictions of treating rodents humanely, and it was the most difficult thing he had ever tried to put into words. “Can we, as a humanity, be humane to this animal?” he said. “The answer is a very cold, hard no.”In Culver City, the Schuelke twins caught four rats. One was snapped in a Victor trap in the garage during the night, its neck sliced by the razor blade. Two more were sucked into the Twin Ratvac in the living room. The fourth came as the brothers and two employees were cleaning up the kitchen on the second day of the job. As they moved the refrigerator, a rat jumped out from behind, and one of the employees sucked it up into a bucket with a vacuum.The four men brought the bucket with the rat outside and opened the top. There was an inch of gray liquid at the bottom. The rat was wet, clawing at the smooth walls around it. One of the employees picked it up by its tail as Dave got a couple of close-up shots with his camera. The day was sunny, and a child was playing on a tire swing next door.The Schuelkes often get comments on their YouTube videos shaming them for profiting from killing rats. “Which kind of makes sense in a way,” Dave said. “But in the same token, there are too many rats and they need to be killed.” He noted that he could try to save every rat he found and drive it 30 miles away. But how could he run a business doing that? And what other sorts of environmental damage would that do? “I’m not a believer in saving rats,” he said. “I don’t have a heart for them. ’Cause they’re nasty.”After capturing the rat footage, Dave returned the animal to the bucket. His brother and employees went back to cleaning up the house. Dave stared at the rat and picked up a wooden two-by-four, painted white, that was lying on the ground. He located the rat’s head and crushed it with the short end of the beam. “I don’t want it to suffer,” he said, as he pushed down with all his weight. The rat struggled for a moment, then stopped. “Poor guy,” Dave said, and gave the beam one last push for good measure.