This episode was suggested by a listener and patron, Rachel G. If you'd like to suggest a topic, you can do so on Facebook and Instagram at Morbid Curiosity Podcast, on Twitter, at Morbid Podcast, and on our website, www.morbidcuriositypodcast.com. This episode contains discussions about animal testing, extermination, and blood sports. If that's not something you want to hear about, this may be a good episode to skip.
Humans are fascinated by gore and violence, but even more so, the mysterious and unsolved. Interest in these disturbing and unpleasant subjects is called Morbid Curiosity, and it has gripped hundreds of people throughout the ages. I am one of those people. My name is Halley, and this is the Morbid Curiosity Podcast.
There is no animal that humans are so starkly divided about than the rat. Many feel disgusted or even afraid of rats, and believe they are dirty disease carriers who brought on plagues that decimated Europe in the past. Others find them as perfect animal models, integral for scientific research and psychological testing done in laboratories all across the world. Still, others find them to be wonderful companions, capable of affection and great intelligence.
These three images of the rat developed over the course of history, and while the wild disease-ridden version of the rat is certainly ingrained in most human populations, the other views of the rat are quickly becoming more mainstream. In this episode, we'll talk about how each view came to be, and how rats are more like humans than most people think. But first, let's talk about what rats are, their origins, and how they spread to almost every continent of the world. Rats are mammals of the Order of Densha, or rodents.
They are separated from other mammals due to the presence of a single pair of large front teeth, or incisors, in the upper and lower jaws that grow continuously, which is why rats must gnaw in order to keep their teeth at a manageable size. The stereotypical rats that most of us think of, when we hear the word rat, come from the genus Ratus, and are the black rat, or Ratus Ratus, and the brown or Norway rat, Ratus norvegicus. It is the wild brown rat that inhabits most city sewers and alleyways today. It is also the brown rat that makes up the majority of lab rats and fancy or pet rats, although these fall under the scientific name Ratus norvegicus Domestica to differentiate them from their wild relatives.
Both black and brown rats have very distinctive tails, which are long and hairless. These two species of wild rats are commensal creatures, meaning they depend directly on humans for food, and therefore live permanently alongside humans. They are omnivorous, meaning they will eat plants, meat, and insects. They tend to feed on refuse and garbage left out by humans, as well as bird eggs and ripening grain, fruit, and vegetables on farms, but they're also attracted to wires, wood, plastic, leather, cloth, and other non-food items.
Rats, like most rodents, are nocturnal, meaning they only come out at night. Unlike most nocturnal animals, however, they have poor eyesight and mostly find their way around using their incredible sense of smell. They also have an excellent sense of taste and quite the sweet tooth. They are very agile on land and in water.
They're also good diggers and can create burrows or nests anywhere there is dirt, including under sidewalks. The entrances to these burrows are usually only about two inches wide, which is the size of the rats skull. They can collapse the rest of their skeleton to allow passage into the burrow. Rat burrows always have a hidden exit for quick escape called a bolt hole.
They are lined with soft materials like grass, small plants, and more modern-y plastic bag shreds. Wild rats also sometimes nest between the floorboards of buildings in the corners of underground or subway stations, sewers, basements, or cluttered alleyways. These locations are desirable because of the vast food supply of human garbage and refuse that end up in these locations. Areas with rat problems are usually areas where humans have left out food, garbage, or other ways, which attracts the rats.
Both black and brown rats reproduce very quickly, with males copulating with many females in order to produce young, as is the case with most mammals. Once pregnant, female rats usually give birth after 21 days of gestation, with the average litter size being 8 to 10 pups. Female rats can be pregnant again almost immediately after getting birth. With this high reproduction rate, one rat nest can become a colony of over 50 rats within six months.
Rats are also very social creatures and can create vast networks of dens. There are often alpha males who lead colony groups in search of food or defend their small territory from other animals, including other rat colonies. These scuffles usually end when the other rat group runs away. Fun fact, a group of rats is called a mischief.
Rats are shy of new objects or food in their territory, which is why many times when traps are set to kill rats, the rats will disappear before being caught in the traps. This behavior is unique to rodent species that live alongside humans. Therefore, it's been theorized this wariness developed in order to avoid human methods of extermination. This suggests that rats are incredibly adaptable and intelligent.
Wild rats tend to push other animals out of whatever habitat they move into by reproducing rapidly and consuming all available food. They can eat, destroy, and contaminate crops and crop stores rapidly. Wild rats also carry diseases in their bodily fluids that can affect humans, as well as fleas and mites that can also pass rodent diseases onto humans, which is part of the reason human hatred of rats is so deep-seeded, but we'll get to that in a moment. As rats are found wherever humans are, the history of rats is interwoven with human history.
It's theorized that the ancestors of black rats originated in Asia and slowly spread westward. In East Timmer near Indonesia, fossils of ancient now extinct giant rats have been found that date to the Upper Paleolithic around 44,000 years ago. Many of these fossils show signs of burning, which suggest they were being eaten by humans. Archaeological remains of rat ancestors have also been found alongside human remains from the Neolithic in India, around 12,000 years ago.
These remains are hard to find as they are quite small and often destroyed over time. There's a carving from ancient Egypt that shows rats laying siege to a fortress occupied by cats, and rat traps have been found that date to the Middle Kingdom between 2055 and 1650 BCE. Evidence of rats in the Mediterranean appears between the 4th and 2nd century BCE, when black rats replaced local rodents. They likely came to the Mediterranean via human trade routes, both land and sea.
They had reached Spain by the 2nd century BCE, and quickly spread northward on Roman carts and ships loaded with food supplies. As mice and rats look rather similar, the ancient Greeks didn't differentiate between them, making it hard to track the presence of black rats in written sources. We know they were considered a pest, however, as the god Apollo was in charge of destroying them. Rat skeletal remains have also been reported in a Roman well dating to 300 CE in the north of England near Hadrian's Wall, which suggests they were in Britain during the Roman occupation, and therefore traveled with the Romans.
Archaeological evidence of black rats first appears in continental Europe between 400 and 1100 CE, but they could have been around earlier. By the end of the first crusade in 1099, black rats had spread all across Europe, still following human travel very closely by both land and sea. Before the end of the 13th century, they were well known as pests, as indicated by the popular story of the Pied Piper of Hanlon, which first appears in 1284. By the late 1500s, the black rat was such a nuisance in England that there were days of prayer dedicated to begging for protection from them, and rat catchers became a very important profession.
It was also during the black rat's reign over Europe that a series of devastating epidemics of plague occurred. This is likely due in part to what is known as the Little Ice Age, which ran from 1350 to 1850, and was a time of cooler weather which resulted in famine, epidemics, and general chaos. Due to the change in food availability, rat and human populations would have gone through several boom and bust cycles, and during years of overpopulation, a strong environment was created for the cultivation of disease and epidemics in both rats and humans. The rats likely played a role in human epidemics, but how big of a role is uncertain?
I'll get into that in detail after the break. Near the end of the Little Ice Age, there was a sharp decline in black rat populations, as they were rapidly replaced with brown rats, who also seemed to spread from Asia. Brown rats have since taken over the world, existing on every continent except Antarctica. They didn't replace black rats completely, however.
There were and are pockets of black rats near the equator, so it's possible brown rats took over the colder habitats, which they seem to be more suited to. Today, the two species exist together, but inhabit different territories in buildings in modern cities. Brown rats mostly stick to sewers and ground level areas, while black rats are more often found in attics and rooftops. However, it is the brown rat that most people see in their minds eye when someone says the word rat.
Brown rats were reported in England in 1728, in France and Italy in 1750, and in Norway in 1768. They came to America with British colonists in 1775, and reached California by 1851. Like the black rat, they drove out every competing rodent or animal thanks to their ability to eat anything and live anywhere. The three versions of the rat, plague, lab, and pet, seem to originate in the late 1800s, although the concept of the disease-ridden rat is far older.
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And now, back to the podcast. While it's true, there is a large population of people that love and appreciate rats, most humans see rats as disgusting, or associate them with dirt and disease. This new is an ancient one, and while rats don't deserve all the bad press they get, there is some historical evidence that they contributed to one of the most famous pandemics in history. The negative few of rats began not with disease, but pestilence, which, in ancient terms, meant a plague on crops.
In ancient civilizations, rats had a huge economic impact on human populations, as they ate grain harvested and stored by humans, and contaminated more than they ate with their feces. In a developing society with a rapidly growing population, where strain on the food supply is already felt, rats and mice were a heavy burden. Dense rat populations are brought on by ample food supply, be it due to a wet year with plentiful crops, or a bad year in which crops are gathered and stored to ration over a long period and end up spoiling. In fact, rats and mice were so associated with grain and food spoilage that it was commonly believed that rats and mice were spontaneously born within containers of grain or rotting food.
This concept was first mentioned in Classical Greek texts and was carried all the way up into the 16th century. Unfortunately, a dense rat population is the optimal condition for the spread of disease among the rats, and as rats live mostly among humans, that disease can sometimes affect humans as well. Long before germ theory revealed that rats can carry pathogens that cause disease, humans feared and pursued rats. Ancient people seemed to know rats had something to do with disease, but they weren't sure what.
It was obvious, however, that some diseases spread through physical contact, including human and animal contact. Hence, quarantines were invented in 1377 in Venice, which we talked about in our Pavalia episode. Plague, also known as bubonic plague, is mainly eroded disease, but has broken out among humans many times throughout history. Plague epidemics weren't as great or far-reaching in ancient history because there were fewer dense urban populations of humans, and therefore fewer dense populations of rats.
But as human civilization grew, this changed, most historians' interest in rats comes from their association with the Black Death, a massive outbreak of plague that went from 1347 to 1351. The Black Death is traditionally thought to be caused by the bacterium Yersinia pestis, which was carried in the belly of Xenopsilia Chiapas, a type of flea. These fleas invested the Black Rats of Europe around the time of the Black Death. Rat blood has the ability to withstand enormous concentrations of plague bacillus, but they can still be killed by it.
When a rat died from the plague, their fleas were forced to seek other warm-blooded hosts, which included humans. The fleas then regurgitated the infected rat blood into their new hosts, infecting them. Rats, therefore, aren't the true cause of the plague, but assist and amplify its spread. After the plague infects humans, plague bacteria collects in the lymph nodes, which causes them to swell, causing painful lumps called boobos.
This was accompanied by high fever and black patches on the skin, which is how this outbreak got the name, the Black Death. Without modern treatment, 50% of infected people die within a few days. Another form of the plague is the Septosemic Plague, in which the infection is present in the blood, as well as the lymph nodes. In this form, fleas can transmit the plague from human to human without the assistance of rats.
The third and final form of the plague is the Pneumatic Plague, which affects the lungs, and without modern medicine, causes death within 14 hours of infection. This form spreads incredibly rapidly, as coughing and sneezing transmit the infection to others. Long after the Black Death, smaller and smaller outbreaks of plague continued into the pre-modern and modern period. In the 1890s, it was discovered that black rats could carry plague bacteria, and from this moment on, they became the object of much loathing and fear, and it was theorized that they were the cause of the Black Death and the other outbreaks of plague over the centuries.
By the way, dogs and cats can also carry the plague, but have somehow evaded the same bad reputation as black rats. A 2011 study by Barney Sloan of English Heritage suggests that archaeological evidence doesn't support black rats as the main spreaders of the Black Death in London. If they did spread the plague, there would be documentation of both a large amount of rats and then a large rat die off, and archaeology would reveal many rat skeletons who died of the plague, but that isn't the case. The archaeology could be skewed as rat skeletons don't survive well due to their small size, but people would have written about hordes of live rats and piles of dead ones.
He also suggests that the plague spread far too fast for rats to be the only vehicle for its spread. A 2018 study suggests that human parasites, like fleas and lice, also spread the plague. Catherine Dean of the University of Oslo found that the rat parasite to human pattern of infection does not match the pattern of infection and mortality reported during the Black Death. A closer match is infection spread through human parasites.
This, combined with the two other forms of the plague, are likely would cause its rapid spread across Europe. More research is needed to confirm this, but it supports a rising body of evidence that rats and their fleas were not solely to blame for the Black Death. Today, scientific testing has confirmed that rodents do carry some infectious diseases. One known to be carried by brown rats is leptospirosis, also known as mud fever, which is spread when rodent urine soaks into mud and is then absorbed by human skin, especially if there are cuts in the skin.
Human infection by such diseases is usually accidental, and prevention is possible by improving hygiene, removing the rat's food source, and therefore removing the rats. So yes, it's true that rats can spread disease, but improvements in public health and hygiene standards since the Black Death have diminished the risk of infection. However, the idea that they may have had a hand in the worst epidemic of plague by a flea bite has solidified this reputation of disease-carrying since the Victorian era. Human disgust with rats may also originate in the Victorian era.
The word disgust originates in Victorian England and was used to speak of lower body functions. Since rats inhabit sewers where humans most disgusting body functions end up, their reputation went from something terrifying to something disgusting. However, during the same era, brown rats also became domesticated on a large scale, as pets, and then as laboratory animals. These two new forms of the rat possibly came from a single source, the rat-baiting pits of London.
Rat-baiting was a popular sport in England and France in the 1800s, in which hundreds of rats were caught and placed in a pit, and a terrier or other ratting dog was then set loose in the pit. Bets were taken on how fast the dog would kill all the rats. The catching and breeding of rats developed in order to both read the city of the rodents, as well as provide rodents for this blood sport. One famous rat catcher and breeder was a man named Jack Black, who was the certified rat catcher to Her Majesty Queen Victoria.
Black often walked around London peddling his own personal recipe for rat poison, and demonstrating its potency on caged rats he carried with him. He also caught and bred brown rats for the rat-pits, many of which he sold to a man named Jimmy Shaw. Shaw was an innkeeper and the owner of the largest rat-pit in London. He bought rats from Black, as well as many other people in London, and used them for his rat-baiting spectacles.
Fortunately for the rats, rat-baiting was banned in the 1870s as contemptible and cruel. As they bred brown rats, Black and Shaw began noticing new colors of fur develop among the rats. Black and Shaw began selling the more unusually colored rats as exotic pets and curiosities. This is when white and albino rats were first bred and sold as freaks of nature, along with pied rats and other varieties with very long tails and bigger ears.
These new and unique rats became quite popular among upper-class ladies to display in their homes. This is how the pet rat and possibly the laboratory rat became separated from the wild rat and how they became colorful and acclimated to human handling. The transition from vermin to pets dramatically altered the social identity of rats, moving them from the sewers to a place of nobility. Keeping rats as pets became very popular in the early 1900s, thanks to a British woman named Mary Douglas, who encouraged young people to become rat-fanciers, or people who bred and kept rats as a hobby.
She also organized rat shows in the same vein as cat or dog shows. Unfortunately, after her death in 1921, the popularity of rats as pets faded. However, in the late 1970s and early 80s, rat-popularity grew with the rising acceptance of alternative, fringe, and previously stigmatized communities where rats have long been accepted as excellent pets. Today, there are fancy rat societies in most European countries, in Japan, Australia, and the USA, that publish magazines and books promoting what excellent pets rat-snake and putting on rat shows.
Fancy rats offer companionship similar to that of a dog, but on a smaller scale, which is how they get the nickname Pocket Dogs. They are also affectionately known as sewer-puppies, which, by the way, I think is adorable. They are sweet-natured, gentle, affectionate, and clean. They can be trained to use a litter tray and are consistent groomers similar to cats.
They are also very social, bonding closely with other rats and their human family. They are playful, curious, and smart enough to learn tricks. They live longer, are more colorful and smaller, and have bigger ears than their wild brown rat relatives, and they pose no more health risks than any other common pet. Unfortunately, just like with other pets, selective breeding for competitions has led to many pet rats being abandoned when they don't conform to specific categories.
This has led to the development of non-profit rat rescues, one of which is run by MCP listener Rachel. Rachel has created Rachie's Rat Tyrant Home, where foster carers and volunteers seek to educate people about pet rats and rescue those that have been abandoned. Rachel also runs a small museum of rat pathology. Rachie's Rat Tyrant Home is the first rat infrastructure of its kind in Brisbane, Australia.
Other areas of Australia, such as Melbourne, have a well-established pet rat community, and the Australian rat fancier society often puts on picnics that include rat cuddling. If you'd like to know more about Rachie's Rat Tyrant Home, you can go to facebook.com slash Rachie's Rats, that's R-A-C-H-I-S-R-A-T-S, and support this great cause. The third version of the rat that most people are familiar with is the laboratory rat. These rats also became distinct from wild rats in the Victorian era.
Similar to the pet rat, the transition of the brown rat from vermin to lab specimen was a dramatic advancement in its social identity. There are several ideas on how rats moved into the realm of science, but the use of rats as laboratory specimens is considered to originate with the Whistar Institute, America's first non-profit institution solely focused on biomedical research and training, which was founded in 1892. It was at Whistar that the first commercial rat colony was established and began research into how the rats could be utilized in biomedical and psychological research. The first research study using rats was an 1894 study on the effects of diet and alcoholism at Clark University in Massachusetts.
In 1900, white rats were used for maze-running experiments by psychologist W.S. Small, also at Clark University. Maze tests in the 1920s showed that rats were capable of learning and adapt rapidly to changes in their environment. In the 1940s, Oxford University was one of few places to be studying the science of wild rat behavior, also called ethology, in order to better utilize the rat in laboratory experiments.
Thus began the white rat's career as a scientist and animal model for the study of human physiology and psychology. This role was later taken over in part by white mice, but it began with rats. They were thought to be the perfect generic laboratory mammal. Their cardiovascular system is very similar to ours, especially their hearts, and they display a range of emotion and behaviors similar to humans.
Laboratory rats serve several purposes, unfortunately not all of them very nice. Medical testing usually involves injecting or feeding a rat substances that are theorized to treat certain conditions or have certain effects on humans and observing what the substance does to the rat. Testing organ transplant methods, drugs, and cancer treatments on rats and mice is also a large part of medical research. The rat is done so that no humans are harmed in the process of testing medicine.
Psychological testing usually involves placing a healthy rat in a certain social or physical situation and observing their reaction and behavior in order to better understand human behavior. Psychological testing of group behavior is most often done using rats as they are social and possess metacognition, which is thinking, knowing, awareness, memory, and learning capabilities. Rats are still used in laboratories today because we share 90% of our genes with them. They have accelerated evolutionary adaptations, meaning they respond to changes in their environment on a genetic level quickly due to their short lifespan and quick breeding capability.
They are intelligent and show emotions similar to that of humans, and they cannot lie, which makes their responses to testing non-biased, especially in behavioral testing. Humans are natural liars or justifiers of their behavior to themselves and others, making it hard to do any sort of behavioral testing on them. While rats are still used in laboratory testing, the old days of housing them in individual wire cages are over. Laboratory rats are now housed in colonies and in conditions that mimic more closely their natural environments.
They are fed well, kept healthy, and given good lives, partially because healthy, happy rats make for more accurate test subjects, but also because there are laws in place to make sure they are given ethical treatment by the scientists with whom they work. They are living creatures who deserve ethical treatment. Still, many animal rights groups are very opposed to the use of animals in laboratory testing, as many of the tests result in pain, suffering, and death for the rats. Testing on humans is unethical, therefore rats are used as a stand-in.
This causes controversy, especially when it comes to cosmetic testing, as it is seen as cruel as well as unnecessary, but that is the subject for another podcast. Rats have become essential to medical research. It is estimated that one scientific paper that has used rats for their research is published every hour to this day. Without the input of rats, the scientific process would be impossible, so their importance should be reiterated.
Without rats, we wouldn't have much of the medical knowledge we have today, and for that rats deserve our appreciation and respect. Depictions of rats in fiction are often villainous, and they have been used as a tool of the horror genre since before Edgar Allan Poe used them in his short story, The Pit and the Pendulum. They have been used often as villains in fiction, such as in the Red Wall books, The Great Mouse Detective, and Willard. Plague rats specifically have made it into modern video games such as League of Legends, Dark Souls, Dishonored, and of course, a Plague Tale.
However, thanks to our dualistic view on rats, they have also been represented as good-natured heroes, such as Remy from Ratatouille, Nicodemus from Mrs. Frisbee and the Rats of Nim, and Master Splinter from the Teenage Mutant Ninja Turtles. The identity of the rat in human culture varies greatly, depending on the life it's born into, Wild, Domestic, or Laboratory. Their astounding adaptability is what makes it possible for them to inhabit all three categories at once.
We fear rats because they are smaller versions of us. Like us, they have conquered every continent, consumed their way toward famine, and are incredibly adaptable, depending on their situation. No other animal has ever competed with humans to the degree that rats do and survived. Rats live in the same world as we do.
Their filth is really our own. They point out to us how gross we are, as well as help us towards our goal of better health and hygiene. They are also our friends, smart, empathetic, and loving. This triple view of the rat, disgusting, insightful, and adorable, is why these interesting creatures spark our curiosity.
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