Rats and Human History
“You Dirty Rat!”
This is a very famous line from a movie from around my parents’ era, so forgive me for not being certain of the origin, but I believe it was James Cagney, in one of his many “tough guy” roles in the early movies.
Now this was a pretty disparaging insult that was thrown at whoever it was Mr. Cagney was sparring with – to equate someone with something as low and vile as a Rat. Was it deserved? Do rats really belong near the bottom when it comes to desirable things we want around us? Well, possibly, but it takes some understanding of “rats”.
There are many, many species of rats in the world and in the United States. Most of the kinds we might find around us are native to our country, and therefore of very little problem as “pests”, although this cannot be an all-encompassing statement. After all, even our native species are rodents, and as rodents they may still gnaw holes in our possessions or be associated with parasites on them that can be a problem for us. For example:
Wood Rats – also called “Pack Rats” because of their desire to collect odds and ends that we might leave sitting around, and store these collectibles in their nest. Often Wood Rats will make their homes near our own structures, and it is common for Kissing Bugs to be associated with the rats and their nests, possibly leading to attacks on people as well.
- Cotton Rats – native to the western and southern U.S. these rats are well known for damaging crops grown for human food.
- Deer Mice – while not rats, these mice are now well known – and feared – for their association with a nasty disease called Hantavirus, which has killed many people in the western United States in the past few years. The virus is passed with the feces and urine, and when dry and dusty it can be inhaled by people who are cleaning or working around areas that are contaminated.
So, even valuable native species of animals can interact with humans in a negative way. This certainly doesn’t warrant wholesale slaughtering of the animals, but does suggest we understand them and avoid the potential problems.
However, there are 2 species of rats in our country, very widespread in their range, that DO NOT BELONG HERE, and these are the Norway Rat and the Roof Rat. Both species are native to eastern Asia, but hundreds of years ago managed to hitchhike on ships that sailed across the Atlantic Ocean and found North America to their liking as well. As with many imported “exotic” species there are no specific natural controls for these rats in the U.S., and they can live and breed with relative impunity. Of course, many of them become cat food or are eaten by predators such as owls, but since these two species have chosen to live closely with humans there are few owls and other native predators available, in our cities or urban neighborhoods, to control their numbers substantially.
Some other common names for these two rats might be:
- Norway Rat – sewer rat, brown rat, wharf rat, ship rat, burrowing rat, house rat
- Roof Rat – black rat, tree rat, climbing rat, gray-bellied rat
These common names are descriptions of the appearance and habits of these rats. The Norway Rat is an excellent swimmer, and is found often around waterfront areas, in sewers or storm drains, on board ocean vessels, in our homes, or in its underground burrows, where it prefers to nest. The Roof Rat is a phenomenal climber, easily scurrying up trees, power poles, sides of houses, or wires running along the streets carrying telephone cables. They prefer to nest above ground, perhaps as an escape from the Norway Rat, and commonly nest in trees or thick shrubbery, as well as in the attics of our houses.
So, what are the redeeming qualities of these two species of rats in the United States. I have carefully listed all the positive reasons for having these exotic animals around us, in the box below.
Now, this may seem a little overly harsh. After all, they are warm-blooded animals that feel fear, pain, anxiety, etc. Shouldn’t they be nurtured and protected? I believe offering aid and comfort to exotic pests is short sighted. They have been shown quite positively to be damaging to our environment, in the sense that they compete with native animals for space and food, feed on eggs and young of native animals, and in general do harm to the natural flow of our environment. Their introduction to the delicate natural environment of Hawaii has been shown to be devastating to native species there.
While even most pest control professionals feel some remorse at killing rats, they do so with the recognition that these animals fiercely compete with humans for our health and our homes.
How do rats affect us?
There are many important ways, but we might place them in the following general categories:
Food – worldwide, rodents destroy about one half of the food we produce, most of this due to contamination of the food with excrement. Rats eliminate an average of 20-50 droppings per day, along with an ounce of urine, onto whatever surface they are on when the urge hits.
Damage – due to their constant “gnawing” rodents destroy our possessions, and it is believed that about one third of structure fires of “unknown” origin likely are caused by rats chewing on electric wires.
Disease – rats carry parasites such as fleas, mites, and lice, that have been responsible for the deaths of many hundreds of millions of people in human history. Even if they are not spreading a life-threatening disease to us, parasites such as Tropical Rat Mites feed on people who live in a structure with a rodent infestation.
- Attacks on people – as awful as this may be to admit, rats will readily feed on humans if we will hold still long enough. There are numerous reported cases of attacks on people in the past few years, particularly babies, who were attacked by rats as they slept in their cribs. Rats eat a wide variety of foods, including flesh, and infants may be helpless to escape.
Without a doubt, the most notorious example of the devastation wrought by rats was the horrible epidemic, in the 14th century, of a disease referred to as “Black Death” due to the blackened color the skin on infected people. Black Death is more properly known as Plague, or Bubonic Plague, and is caused by a bacteria that first is spread from infected rodents to their fleas, and then from the fleas to humans who are living in close association with rats. The disease can then be passed from person to person as Pneumonic Plague by coughs or sneezes. In three recorded “pandemics” in human history, where plague spread throughout the world, hundreds of millions of people have died, and human history has been altered.
Plague exists today, and occurs regularly in some undeveloped countries where rat control still is not undertaken well. In the western United States the disease is firmly in place in native rodents, such as ground squirrels, and human cases occur once in awhile. Roof rats and Norway rats are not the prime culprits here, but they easily could be again. An outbreak of bubonic plague in San Francisco, early in the 20th century, killed several dozen residents of the city and was associated with Norway Rats.
The name “Rodent” means “gnawing teeth”, and describes one prominent trait of all rodents very well – they gnaw, or chew on things. Of course, this may be because they are planning to eat the object, such as fruit or nuts, but often it simply is for other reasons that are equally destructive.
- Entrance to structures – while rats can squeeze themselves through a hole only ½” wide, they would prefer not to, and usually will chew large holes in walls or under doors in order to move through more easily.
- Incisor teeth maintenance – the front teeth in a rodent’s mouth are called incisor teeth, and they grow at a rate of about one half inch per month. These teeth are harder than iron and are operated by jaws that can exert a pressure of 7,000 pounds per square inch. Since the 4 incisor teeth butt against each other they keep themselves worn down properly, along with the wear from gnawing.
Were it not for the damage caused it might almost be humorous to see some of the items with holes gnawed in them by rats – drain and sewer pipes, underground sprinkler piping, prescription pill bottles, furniture, walls inside homes, doors, and many, many other items and surfaces. It is not uncommon for pest control technicians to find their plastic bait boxes, placed as a containment for rodent bait, to be badly chewed upon. One person even found a plastic trap, designed to capture the rodent alive, with a hole gnawed through one end to afford the escape of the captured animal.
Dealing With Rats
So, clearly there is a danger to allowing these exotic rodents to co-exist with people, and the ultimate desire would be for them to be completely eliminated from those regions of the world where they do not belong. This, however, will never happen. They are too adaptable, hide too well, and breed too quickly. Thus, our next best option is to ensure they cannot cause us problems in our homes, and the way to do this is to close our home off, eliminating access to the inside and eliminating food and shelter outside. Some ideas here are:
- Close off any opening more than one-half-inch wide, with wire mesh, wood, foam sealant, or any other closure that will exclude the rodent. Wire mesh is nice, because rodents do not like to chew on it in an effort to reopen the access.
- Rodents already suspected of living inside should be trapped and eliminated. Honestly, catching them alive and releasing them outside is not a good answer, as it simply transfers the problem from one location to another. It is best to avoid using rodent poisons inside, as rodents that die from this method are likely to die where you cannot find them until they are smelling the place up and breeding flies.
- Traps should be attached by wire to something nearby, so the rodent cannot drag it away. Inspect traps frequently to allow removal of the rodent once caught.
- Eliminate as many sources of food as possible. Don’t leave pet food in dishes outside, or even in the garage if rats have an easy access to garage interiors. Pick up fruit and nuts that have fallen from trees on your property. Keep garbage can lids on tight. Eliminate garden snails if you are unlucky enough to live in an area that is infested with them.These “domestic” rats are problems, but because of the fact that they are warm-blooded animals there are emotions stirred up over causing them harm. However, there certainly is a strong argument that it is hazardous to human health and to our possessions when rats and mice live in and around us, and eliminating the rodents is a wise step toward maintaining good public health.