Except for scientists who experiment on lab rats, many people scream at the sight of these creatures or try to kill them. The blanket perception is that rats are useless vermin. However, the truth is more unusual.

These highly intelligent mammals have jobs in the military and medical sectors. They rescue their fellow rats and communicate over the Internet. They even regret things and teach their kids about dangers. In the end, they may survive Armageddon and dominate the world.

10 Distinct City Groups

During a 2018 study, four cities were chosen and 150 rats were captured from each. They came from Vancouver, New York, New Orleans, and Salvador, a city in Brazil. Each rat’s tissue sample was analyzed for 15,000 genetic markers.

The results confirmed a theory from the previous year when it became clear that a commercial district in Manhattan divided most of New York’s rats. The suspicion that the separation created two genetically distinct groups was proved when the 2018 study confirmed “uptown” and “downtown” rats.^[1]

The three other cities also showed DNA divides. In New Orleans, rats from the French Quarter and the Lower Ninth Ward were genetically distinct. They were separated by a canal. A valley split Salvador rats into a northern and a southern group. A Vancouver pocket was isolated by highways.

The report also found that rats from smaller areas preferred their own. Especially in New York and New Orleans, rats with related DNA were more apparent within 460 meters (1,500 ft) of one another.

9 Males Without Y Chromosomes

In mammals, gender is determined by the X and Y chromosomes. Offspring inherit one from each parent. An XX combination creates a female, and XY is needed for a male.

However, Japan’s Amami spiny rat is the exception. The species has no Y, and yet some are born as fully functional males. Even more odd, both genders only have a single X chromosome.^[2]

A 2017 study took stem cells from a female rat’s tail and injected them into mouse embryos. Female mice carried these to term, and the pups revealed an interesting clue. The spiny rat’s stem cells had adapted to both ovaries and testes. The latter was a world first.

In the past, sperm could not be grown from female stem cells due to a lack of the male Y chromosome. However, spiny cells proved exceptionally flexible and sensed when they were in ovaries or testes.

Researchers also found that the male rats kept their other male sex genes. When the Y was mysteriously erased, these jumped to other parts of the genome and the remaining X.

8 They Inherit Fear

A 2014 experiment showed that rats taught their offspring about danger. Scientists first conditioned adult females to dread the scent of peppermint. Every time the aroma was released into the rat’s enclosure, she received a mild electric shock.

The herb-fearing rats later became mothers, which initiated the second phase of the experiment. No more shocks were involved. But when the peppermint smell came, the adults stressed and their bodies released a certain smell.

The pups noticed both smells and their moms freaking out. Soon, they learned to fear peppermint, too, even though they were never shocked. They were simply taught by their mother’s behavior that this change in their environment was a danger.^[3]

They understood this lesson within a few days. Soon, the pups even feared peppermint without their mother’s presence. This infant perception of danger could be one of the things that make rats such a successful species.

7 Regretful Rodents

In 2014, researchers built a restaurant for rodents. This was to test if rats could feel regret. The “restaurant” was a circular enclosure with rooms. Each chamber dispensed food after a certain waiting period. The rats were trained to gauge the different waiting times from chimes.

Some rats were willing to wait an hour for their favorite dish. Less patient individuals decided on a shorter time and grabbed the next-best meal. Since they could not reverse their decisions, this left some room for regret.

Researchers found that rats which chose the worse deal often glanced back at the room they skipped (holding their favorite snack and longer waiting time). At that moment, brain scans revealed a curious thing.

As the animals looked back, their brains showed what researchers analyzed as “a representation of entering that restaurant—not of the food they missed.” This was the first evidence that animals other than humans could regret a choice.^[4]

6 Bomb Squad Rats

In Mozambique, being an African giant pouched rat can get you special training. These cat-sized critters can solve one of the country’s deadliest problems—land mines. When a young rat is interested in this career path, it enters a Belgian organization called Apopo. There, it receives nine months of training with lots of yummy food rewards until it can detect the scent of explosives.

Once ready, they go out into the field with mine-removal experts. When a pouched rat smells a mine, it scratches at the ground. This alerts its handler, who is at a safe distance.

The rats are in no danger—they are simply too light to trigger the mines. Additionally, they are so good at their jobs that they can clear an area in just 30 minutes. It would take experts three days to sweep the same place with metal detectors.^[5]

Mozambique was rigged with thousands of land mines during its 16-year civil war. Although the conflict ended in 1992, the explosives continued to injure and kill people. Thanks to a small army of rats, Mozambique will be land mine free.

5 They Could Rule The World

In the past, Earth experienced at least five mass extinctions. Most recently, the dinosaurs perished around 65 million years ago. This event allowed tiny mammals to take over the world.

In 2014, scientists held a thought experiment. They reviewed geological records, past extinctions, which species thrived, and how. The idea was to see which animals would likely survive the next great extinction and take over the world.^[6]

Drawing on the past, some clever calculations, and present species with Armageddon-resistant skills, the researchers identified the winner. Rats, sure, but no ordinary ones.

Mass extinctions have a way of beefing up the tiny underdog. Should rats emerge victorious after a global disaster, they could become massive in the absence of predators. Cats and pigs were also candidates, but the rodents had a proven history of surviving most environments and eradication programs. Humans did not make the cut.

4 Rats Detect Childhood TB

In 2016, tuberculosis (TB) killed 1.3 million people, including 130,000 children. TB is difficult to treat, but kids face an additional hazard. They cannot produce enough mucus and saliva to provide a proper sample. As a result, a child with TB has a 60–70 percent chance of testing negative. So, it appears as if the youngster does not have the disease when he actually does.

Doctors in Mozambique and Tanzania heard that other lung diseases often had distinctive smells, and this gave them an idea. Tuberculosis produces certain compounds which were used to train rats.^[7]

Traveling on motorbikes, the doctors collected samples from patients at local clinics. The rodents, African giant pouched rats, sniffed the samples to see how many they could identify as TB.

Normal tests on the same samples detected the disease in kids, but the rats found a large additional number that the doctors missed. The rate of positive identification jumped by nearly 40 percent. Although the animals’ accuracy dropped with adults, they still found more real TB cases than the usual tests.

3 Remote-Controlled Rats

Past studies have produced some impressive roborats. One study involved hooking up animals to a processor, and afterward, some could control a robotic arm with their thoughts.

In 2002, that experiment led to another unusual mix of computer and rodent—electrodes inside brains that steered remote-controlled rats. The animals received training in a weird way.

The electrodes rewarded them with pleasure. Within 10 sessions, they learned to follow directions. Researchers guided rats up ladders and trees and into dangerous areas—all by typing on a laptop. The animals performed correctly for up to an hour.

However, bioethics experts are not happy with the invasive implants and electronic control of another being’s will. Since the project was funded by DARPA, the US military’s research branch, some fear that this is the beginning of the militarization of nature. The researchers involved said that the roborats were created with search and rescue in mind.^[8]

2 They Have Empathy

Rats react to the emotions of other rodents. This is called emotional contagion. It is the same thing that sets off a group of small kids. One cries and the rest might start bawling, although they do not know why. Similarly, rats displayed pain or fear behavior when they sensed it in others.

In 2011, researchers wanted to see if rats had empathy. Emotional contagion could be viewed as a natural reaction, hinged on instinct, but empathy requires a more intelligent approach. The rat must recognize distress in another and then put aside its own fear to provide assistance.

To start with, pairs of rats were kept together for two weeks. This allowed them to bond. Eventually, one was locked inside a small transparent tube. At first, the free rat was cautious about the new development.

Before long, they repeatedly freed their trapped friends. (The tube could only be opened from the outside.) They ignored canisters that were empty or contained stuffed rats. When presented with containers holding tasty snacks and trapped rats, the free rats opened both types of containers and shared their snacks with their formerly trapped friends.^[9]

1 They Use The Internet

There are two rats that shared information over the Internet. One rodent lived in North Carolina and the other in Brazil. Scientists attached devices called brain-to-brain interfaces to the pair of rats, which allowed them to work together with the Internet as their link.

This achievement is remarkable. Although separated by thousands of miles, the rats shared sensory information and taught each other tricks. If one performed badly at a task, its partner appeared to change its behavior to help the other one succeed.

The rats received each other’s brain signals via tiny electrodes inside their skulls that changed neurological signals into an electronic version. In this manner, brain activity was swapped with a high level of success. They even collaborated on more complex tasks, proving that a direct, sophisticated link between brains was possible.

Near the end of the experiment in 2013, several rats on different continents were linked via the Internet. Despite transmission delays and noise, their brain activity still communicated with each other.^[10]

Science has identified somewhere in the neighborhood of 1.2 million different species on the planet earth. Of all those species, few are as disliked as the rat. While some people really enjoy rats and keep them as pets, and evidence shows they are quite intelligent, most people are not so forgiving. They are considered disease vectors, pests, and a danger to public safety. That said, you may be surprised to learn what goes on in the hidden world of rats.

10. NYC has a Population of About 2 Million Rats

There is a common saying that, in New York city, there is one rat for every human resident. That’s not actually true, and humans are far and away the more populous species.Does that mean there’s not an abundance of rats in New York City? Not by a long shot. It was estimated in the year 2014 that there were about two million rats in New York. While that may not be one rat for every resident of NYC, it works out to being close to the population of Houston.

It’s hard to get more recent numbers, also hard to get any accurate numbers if you think about how one might go about accurately counting millions of rats, but if you look back in the past, their numbers are skyrocketing. In 1950 there were only 250,000 of them.

The increase of the rat population by 800% is certainly something dramatic. There’s no telling how close to accurate the number is, it could certainly be much more than 2 million rats at this point, but it’s safe to say that whatever the population is, New York is an absolute paradise for the little rodents.

9. Rats Are Accused of Eating Anything 

Rats are known as voracious eaters. If you work in the food industry, you know you need to be on the lookout for rats constantly, because if they get in they’ll eat whatever they can, contaminate the rest, and potentially put you out of business. This can be at restaurants, warehouses, grocery stores, you name it. And if that were the end of it, that might be reasonable. But rats don’t just eat what you think they’re going to eat. Rats eat everything, or at least they’re blamed for it.

In one case, rats were blamed for eating over 500 kilograms of marijuana. That’s more than half a ton. That story has also been considered a little suspect, but it’s not outside the realm of possibility. And if you are wondering how much money that’s worth, maybe that doesn’t matter either, because rats will eat money, too. One rat was discovered to have eaten close to $20,000 out of an ATM. He died after it happened, but he died a rich man. Well, so to speak.

Rats have also been blamed for eating 34 kilograms of ketamine, drinking 1,000 liters of booze, and more. Again, the rats may just be convenient fall guys here, but it’s the police doing the accusing so no one’s likely to follow up.

8. Rats Cause Tens of Billions in Damages Each Year

If you have had rats in your home before, you probably noticed some of the kind of damage they’re able to do. Aside from chewing through food containers, they’ll also go through your walls, and their urine and feces can ruin your floors and your furnishings. An infestation of rats in a building can cause a heck of a lot of damage.

It’s been estimated that in the United States alone rats cause about $19 billion worth of damages per year. All the way back in 1982, the United Nations reported rats were destroying as much as 43 billion tons of food per year at a cost of $30 billion. Adjusted for inflation that’s about $96 billion today.

7. Experimental Rat Utopias Led to Chaos

In the 1960s a series of experiments known as the Calhoun Rodent Experiments involved the creation of what was a rat, and later mouse, utopia. John Calhoun wanted to study population density and how it affected the individuals in that population. The idea was to provide rats with whatever they could possibly need. 

Calhoun started his experiment with rats in an outdoor pen, and as the experiment grew, more iterations developed with more elaborate setups. What he discovered was that, even if you give rodents all the comforts they could ever desire such as food, water, and shelter in abundance, at some point everything falls apart.

The rats in his experiment ignored certain areas of the habitat and overpopulated others. Soon the rats would only go about their normal everyday behavior if other rats were around. They wouldn’t eat or breed if they were alone. Behavior became erratic and violent with some rats engaging in cannibalism and what was described as “sexual deviation.” Infant mortality rose to 96%. Soon the entire society collapsed in chaos and squalor.

When Calhoun tried his experiment again with a more elaborate setup and mice, the same thing happened.

6. Every 48 Years India Experiences a Rat Flood

Every 48 years in India something called Mautam occurs. This is what they call when bamboo goes to flower, then to seed, then dies. The bamboo fruit appears and as soon as it does a rat flood occurs. It is the sugary bamboo fruit that black rats crave so when it happens, the population of rats will explode. 

After the bamboo dies off, the massive population of rats has to move on to something else. Typically, this is whatever other crops are around, which can lead to widespread famine and loss of human life. 

Even with a bounty placed on rat tails, in 2009 when the last rat flood occurred as many as 1.5 million rats were killed, it had barely any effect on the population

5. The Hanoi Rat Massacre of 1902 Was a Failed Attempt at Rat Control 

In 1902, Hanoi was controlled by the French. As part of their occupation of the city, the French portion was built with an elaborate sewer system, which hadn’t existed before. This was a great treat for the local rats who soon overran the Hanoi sewers.

With Vietnamese rats showing up in French toilets, the population became extremely upset. Especially as incidents of the plague rose as well. Something had to be done about the rats, so the ruling French came up with a plan. A bounty was placed on rats, and each rat was worth money to local rat catchers. People went out and started catching them in great abundance. Yet somehow, instead of solving the problem, the rap population only grew larger.

Turns out, if you pay people to kill rats, it’s much more profitable for them to breed more rats so they can make more money. The plan backfired horribly and as many as 10,000 rats per day were being turned in for profit with as much as double that on some days.

4. Rats Can be Trained for Search and Rescue

Rats are adept at sneaking into pretty much any place you can imagine. And they’ve also been shown to be highly intelligent. While most people don’t bother connecting these two things, that’s not true of everyone. Rats, thanks to these two skills, are being trained as search and rescue workers for things like building collapses. A small, intelligent animal that is able to sneak into the tightest places is certainly very useful in a disaster situation.

A trained rat with a tiny backpack can be sent into a building that may have collapsed because of an earthquake or hurricane. The backpack contains a tracker, camera and a communication device. They can find survivors and allow rescuers to communicate with the survivor and pinpoint their exact location thanks to the rat’s natural curiosity and ability to weave through tight places. They can be trained just like dogs, and learning to hunt down a living person is not that difficult for them. Rats have already been trained to hunt down landmines and detect various diseases and humans by smell.

3. Experiments Show That Rats Can Feel Hopeful and Will Fight to Survive If They Do

It’s not very often that researchers will use rats and experiments that result in good things happening to the rats. That just seems to be par for the course. One of the more depressing experiments that rats have been subjected to is the Drowning Rat Experiment performed at Johns Hopkins back in the 1950s. 

Although the experiments were cruel, the results were also quite interesting.  In the experiment a rat would be put in a bucket of water and the researcher observed how long it took before the rat drowned. It was observed that most of the rats drowned quickly, even though rats are fairly good swimmers. However, some of them could survive for days. The survivors were all domesticated rats. A hypothesis was formed that having a history of being helped by others may have given rats hope that there was a chance to survive.

For the next round, the rats were placed in the water and just before they were about to drown they were rescued. These rats were held and helped to overcome their near-death experience.  The survivor rats were then put in the bucket again later and it was observed that they swam and survived for much longer. The rats had hope that they would survive, so they didn’t give up so easily.

2. Rats Laugh

Pablo Neruda once said that laughter is the language of the soul. If that’s true, then science has apparently proven rats have souls. You may want to think of that before you put on a trap next time. Researchers have showed that rats are ticklish and they actually laugh when you tickle them, though the sound of their laughter is ultrasonic and can’t be heard by the human ear without help. 

Tickling is actually a big deal in neuroscience because of how the brain responds to the stimuli and, in researching how rats react, we have determined that they are definitely deriving pleasure from it and will encourage humans to keep tickling them. 

1. Two Rats Can Become 500 Million in Three Years

One thing that makes an animal a pest is how prolifically it can breed. Rats are incredibly prolific breeders which is part of the reason they can be so dangerous. A pest-control company called Rentokil explained to potential clients just how bad rat breeding can be.

Rats can reach sexual maturity at an age of about four to 5 weeks. Their gestation period is another 3 weeks. A litter of rats can contain anywhere from 5 to as many as a dozen babies. A female rat can produce as many as 6 litters in a year. 

Even if a wild rat only lives for one year, which is a common lifespan, that means one rat could have produced as many as 72 babies. But you also need to remember that those first few litters of rats would have come of age in the same period and started breeding as well. The result is that in a single year, you could end up with 1,250 rats, just from that one initial breeding pair. 

If you extend your timeline a bit, blow up that one year into three years, that one pair of rats could eventually become half a billion. Obviously that’s an extreme example, and there would be predators, disease, competition and so on that would keep the population down. But theoretically it’s possible, at least biologically, that one pair of rats can become 500 million.