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May 31, 2012

Black Rats, Brown Rats, and the Plague

I've been spending a lot of time thinking about rats. Thankfully, it is not because I have a problem in my apartment! Unfortunately, for many people in L.A., rats are a serious pest, and it's not just one type of rat. The most serious rodent offenders in our cities are the brown (aka Norway) rat, Rattus norvegicus, and the black rat, Rattus rattus.
 

What species of rat is this?

Here on the North Campus we have camera trap images and footage of rats hanging out underneath the bridge. But what type of rat is this? Since Jim Dines, our Mammalogy Collections Manager, wasn't available, I decided to try and figure it out myself. Doing a Wikipedia search for brown rats, I came across a nice diagram that helped me to make an identification. What species do you think it is?

 

 

 

 

Comparison of the physique of a black rat, Rattus rattus
with a brown rat, Rattus norvegicus, from wikipedia

 

Using this diagram I looked closely at the ears and the eyes of the rat. Based on the relatively large size of the ears and the eyes, I determined the above image was of a black rat rather than a brown rat. I showed the image to Jim and he confirmed that it was indeed a black rat!

 

 

 

 

 

 

 

Black rat (top) and brown rat (bottom) from the Museum collection.
Note the tail to body length ratio.
 

Regardless of the species, why do people hate rats? As I referenced in the introductory paragraph, rats are sometimes pests in our homes, but what exactly do people think about rats? I did a Google search for, "why do people hate rats," and this is what I found. "Cute or not they're germ-ridden disease carrying vermin who in addition, can cause untold damage. THAT'S WHY." I also found this: "Rats are pests to humanity, but I personally believe that people especially hate rats because they subconsciously identify with them and see them as a reminder of themselves." Finally, someone else wrote: "A lot of rat-hatred goes back as far as plague. Rats were responsible for the disease that killed thousands of people."

But, is plague a worry for us today in L.A.? Not really here in the city (I hear a collective YAY)! Firstly, according to the Centers for Disease Control and Prevention the last cases of urban, rat-associated plague occurred in L.A. in the 1920s. However, plague is present in L.A. County, and the principal mode of infection is from infected fleas living on wild rodents in rural areas. These rodents include California ground squirrels (remember the recent blog post?) and chipmunks! According to L.A. public health officials, "the major threat of plague to humans is in the rural, recreational and, wilderness areas of the Angeles National Forest, as well as the Santa Monica and San Gabriel Mountains." But, before you swear off recreating in our lovely parks forever, know that there have only been four cases of the plague in L.A. since 1979, none of which were fatal (another YAY for antibiotics and modern medicine).

P.S., Plague is actually caused by a bacteria, Yersinia pestis, that lives in the blood and other bodily fluids of fleas, rodents, and other mammals.

 



Posted by:Lila Higgins

While I find this interesting I have a question that although does not relate to humans' fear of rats does refer to their association with the Black Death. My history books claim that it was the black rat that spread the bubonic plague, but my home encyclopedias say it was the brown rat. Wikipedia goes on to say that it was the black rat that spread the disease with its fleas, but was reduced when the larger brown rat drove most black rat populations out of urban areas - taking the fleas with them. Which is true? And why can't the rat fleas infect both if they can also infect squirrels regardless of the specific rodent species?

I shoot every rat I see. 69 was the count in 2011.

Nice post. BTW, i love rats. If people knew how smart sweet and sociable they were (talking about fancy rats as opposed to wild rats-and then who knows?-they might think differently. As far as the plague, fleas were the carriers of the disease and spread it to rats. You don't see people jumping on a chair when they see a flea, though....

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