Rats: The Bad, The Good, and The Surprising

Rats are our shadow selves. We live on the surface of a city; they generally live below. We mostly work by day; they mostly work by night. But nearly everywhere that people live, rats live too. Take one year in a typical urban rat colony—how fast might it grow? Researchers estimate that a litter of nine pups 10 weeks into the year would grow to 270 pups by the 30th week and wrap up with a whopping 11,907 rats by the year’s end.

Rats usually reach sexually maturity by 12 weeks, and litters can vary from 2 to 14 pups. Reproductive rates are highly dependent on environment. The more shelter, food and trash, the higher the rat count.(2)

Rats live in colonies of 40 or 50 and sometimes relocate to new homes, but over the course of their one-year life span they rarely walk more than 600 feet from their birthplace. (3)

Jason Munshi-South, an urban ecologist who is an associate professor at Fordham says rats cannot as legend has it, collapse their skeleton to fit through cracks, nor are they especially bold; indeed they’re ‘neophobic,’ which means they won’t touch a new object, even unfamiliar food, for at least two days and sometimes a week.

They nearly always follow the same route to their food sources. They sleep, on and off, for about 10 hours a day, and the rest of the time they travel in tight well-worn paths. Munshi-South’s back-of-the-envelope estimate is that they take at least 2,800 steps a day, compared with the average American human’s 5,000 or so.

New York is a rat’s ideal habitat. Our idea of what a park or public space should look like mirrors its native environment, which contrary to the animal’s common name, almost certainly was the grassy Asian steppe. We mow grass, plant a few shrubs and low bushes, a line of trees. Then we improve on nature by adding a constant source of food, our trash. Now at least two million rats live here, maybe millions more, depending on which scientist you ask, reports Ryan Bradley. (3)

So the claim that New York’s rat population is one rat per human is absurd reports Robert Sullivan, but the United Nations has used it, pest control companies use it; health departments use it. (1)

In early 2019 New York Mayor Bill de Blasio announced an aggressive new extermination plan against rats in the city’s public housing, part of a $32 million effort to reduce rats by up to 70 percent in the most infested neighborhoods. Where are they in New York? Of the nearly 28,500 rat-related complaints lodged in New York, Brooklyn led the way with 10,375, followed by Manhattan with 6,037. (4)

Today in Africa the median farm still loses 15 percent of its yield to rats. In Asia rats and other rodents eat enough rice each yer to feed 200 million people. (2)

On some small, remote islands, rats have done as much damage as human invaders. On Easter Island they’re suspected of having wiped out palm trees by eating all the nuts. On other islands they threaten seabirds by eating eggs and chicks.

Acre for acre there is no real estate in the world of endangered life forms more precious than that of the ocean’s islands. Comprising 5 percent of Earth’s landmass, islands have come to harbor one in every five species of bird mammal, and reptile. They have also shouldered 63 percent of all the extinctions recorded during human history. And most of these owed their endangerment to invaders, particularly of then non-human kind, says William Stolzenburg in his fascinating book, Rat Island. (5)

One of the key culprits was the rat. On almost every one of the islands that bore any sign of Polynesians, there were signs of the rat. The rat often traveled with a purpose, as a snack for the long overseas trips and as a self-perpetuating crop of protein to be planted and harvested in the new homeland. The rats were the great enemies of birds, and any bird living or breeding near the ground had but a small chance of existing.

The trails of carnage led from one-acre islands in the French West Indies to the 607 square miles of Hawaii’s Oahu, across the Caribbean, Mediterranean, and Tasman seas, and across the Indian, Atlantic, and Pacific Oceans. Researchers from the University of Hawaii at Manoa credit rats with having driven or assisted 103 species of birds, reptiles, amphibians, and mammals to extinction. (5)

On Sirius Point, a cape in Alaska, the number of seabirds killed by rats each year are more than those killed by the Exxon Valdez oil spill. Researchers, when talking about Kiska, an island in the Aleutians, said the invasion of a single rat was a fate worse than any oil spill.

Fighting back, conservationists have been trying to eradicate rats with ambitious poisoning campaigns, targeting larger and larger islands. At 1,500 square miles, South Georgia, near Antarctica, is the current record holder. In May 2018 it was declared rat free after helicopters dumped 330 tons of poison in five years on its stark landscape, at cost of $13 million. With the rats gone, conservationists expect to see an explosion in the number of albatrosses, skuas, terns, petrels, and South Georgia pipits and pintail chicks.(2)

Scientists these days are working on what might be the ultimate in rat control: a genetic engineering technique that would spread infertility genes through a wild rat population. If fears of unintended consequences can be overcome, this method might one day enable us to wipe out rats on an unheard-of scale, without poison.

The Good

Not everyone hates rats. Perhaps the world’s only temple for rats is Karni Mata in Rajasthan, India. Here black rats whose wild ancestors may have originated on the Indian subcontinent and learned to thrive in cities are thought to be reincarnated storytellers and are fed milk and food.

Brown rats have been recruited by Dutch police to help forensic firearms experts sniff out gunshot residue. The rats have a highly developed sense of smell, and are easier and cheaper to train than dogs. A spokesman said, “If we have a suspect, the forensic expert takes the residue from the hands and the rats can tell in a few seconds it it’s from a gun.” (6)

The giant African pouched rats claim to fame is that they have proved ideal for detecting land mines without setting them off. This is because the rat has poor eyesight and relies on it sense of smell to navigate the world. Now the rats are being trained to detect the presence of tuberculosis (TB) in sputum samples. If successful this could be a huge savings in time and money for countries in Africa that are lacking in resources. (8)

Warfarin was the first modern anti-coagulant rat poison. The good? Warfarin, is an anticoagulant (blood thinner) that reduces the formation of blood clots. It’s used to treat or prevent blood clots in veins or arteries, which can reduce the risk of stroke, heart attack, or other serious conditions. (1)

Paralyzed rats implanted with engineered tissue containing human stem cells were able to walk independently and regained sensory perception in their hind legs and tail. The implanted rats also show some degree of healing in their spinal cords. The research demonstrates the great potential of stem cells to treat spinal cord injury, although there is still some way to go before it can be applied in humans. (8)

The Surprising

Domestic rats can be more like common house pets than you may think. Like cats, pet rats can actually be very clean creatures, and like some dogs, they can be quick learners. You can teach them to spin or go over obstacles, and they’ll also retrieve items and enjoy interacting with people. They like to play and they’re very social reports Amy Jamieson. (9)

Back to wild rats. In one study, rats freed other rats from cages, even though it gained them nothing and even when they could have gorged themselves on chocolate instead. The researcher behind the study, neurobiologist Peggy Mason of the University of Chicago says that typically, once the helper rat frees his companion, he follows the liberated rat. He jumps on him and he licks him, apparently to console the distressed animal. (2)

Rats laugh and this discovery is just the tip of the iceberg. We now know rats don’t live merely in the present, but are capable of reliving memories of past experiences and mentally planning ahead the navigation route they will later follow. They reciprocally trade different kinds of goods with each other—and understand not only when they owe a favor to another rat, but also that the favor can be paid back in a different currency. When they make a wrong choice, they display something that appears very close to regret.

Despite having brains that are much simpler than humans’, there are some learning tasks in which they’ll likely outperform us. Rats can be taught to reach a desired goal, playing hide and seek with a human, and using the appropriate tool to access out of reach food. (10)

Since the 1950s and 60s, behavioral studies have consistently shown that rats are far from the egoistic, self-centered creatures their popular image suggests. It all began with a study in which rats refused to press a lever to obtain food when that lever also delivered a shock to a fellow rat in an adjacent cage. The rats would rather starve than witness a rat suffering.

When rats received a 10 second tickle from a gloved hand, they responded with a rat version of laughter. The animals seemed to enjoy it—indeed, they ran toward the gloved hand and eagerly chased it around their enclosure. Berlin-based researchers even witnessed a joyful jumping behavior known as “Freudensprunge” that has been observed in other mammals.

Tickling, then induces a primitive form of joy said researchers. The results suggest that tickling is more than a quirk of the nervous system. It may even serve a useful social purpose. Tickling might be a trick of the brain to make animals or humans, respectively, interact and play with each other. (11)

Able to survive and even thrive in the most heavily urbanized places, rats are celebrated—or at lest acknowledged– for their extraordinary resilience.. Yet as understood by a series of new studies, they’re not just fast-breeding and tough. They’re smart.

Researchers showed that in tests whether rats could differentiate between combinations of odors and visual patterns, they could recall dozens and could distinguish between contexts in which they’d previously encountered odors.The findings suggested that rats remember multiple unique events and the contexts in which these events occurred. (12)

Another study involved the ability of rats to detect prosody, or patterns of intonation and rhythm that are fundamental to human language. Researchers concluded that rats can discriminate between words pronounced in different ways. To be clear, the rats didn’t understand language—they were tested with nonsense words– but they did have at least some of the prerequisite abilities humans use to analyze spoken language when they first encounter it.

A third study showed that rats quickly learned to use hooks and rakes to obtain food. They weren’t especially handy with them- given a rake with one end too soft to move food, for example, they kept trying to use it. Still the results suggest that rats understand the spatial and physical relationships between the tool and self. (12)

Scientists indicate that playing hide and seek requires cognitive skills to know where your ‘adversary’ will most likely look to or to find the best hiding place. Their study tends to show that rats have these abilities, which had until now only been observed in primates. (13)

We know that rodents can learn to recognize objects, press bars and find their way around mazes. These tests are often used to study how brain conditions affect cognitive function, but they only capture a narrow window of animal cognition. Scientists wondered if rats could learn the more sophisticated task of operating a moving vehicle.

Rats have mastered the art of driving a tiny car, suggesting that their brains are more flexible than we thought. This ability demonstrates the ‘neuroplasticity’ of their brains say the researchers. This refers to their ability to respond flexibly to novel challenges, showing that rats are smarter than most people perceive them to be. (14)

D. Luckey reports the remarkable survival of a rat colony on Enjebi Island in the Eniwetok atoll. Enjebi is part of the Marshall Islands and site of the “X-ray Nuclear Test” in 1948 during Operation Sandstone. Within one year following four nuclear explosions, healthy rats emerged from the protection of cable tunnels. Pregnancy rates, sex ratios, and average number of embryos per litter were comparable with those found before the four nuclear devastations. The colony rapidly expanded to fill the 250 acre island. No mutations were observed. (15)

Dixy Lee Ray discusses a colony of rats that occupy a mound in the Brazilian area of Morro do Ferro. This is a weathered mound, 250 meters tall that contains an estimated 30,000 metric tons of thorium and 100,000 tons of rare metals. The radiation level is so high that autoradiographs (photographs produced by radiation) show plants on the mound actually glowing in the dark. The overall radiation dose they receive is roughly three times the concentration that should produce tumors or other radiation effects. Yet, no abnormalities were found in the rats that were trapped and autopsied. (16)

Final Words

Robert Sullivan, author of Rats, which is referenced in a number of places in this report, has this to say in conclusion about rats. It’s something we all inherently know but worth repeating: “If you take a map of rat infestation in a city (which is usually a map of where rat bites are reported) and you place it over a map showing the places where somebody ought to be spending more money on social services, more money on repairing the housing stock, or more time just generally caring about the people there, then you will most likely find that they match up pretty closely.” (1)