Most frequently rats die from ingesting poison. I don't know of a precise statistic, but I know that at any given moment there is poison all over the streets and homes of New York, not to mention the rest of America. Sometimes, poison is injected directly into the rat burrow; the rat dies of heart failure or, with the most severe poisons, of damage to its central nervous system--they are found dead on their bellies, arms and legs extended. More often, poison is added to grains and the grain is put into shoe-box-size containers called bait stations. Bait stations are the things that people in cities see constantly in back alleys and in parks and do not recognize or, chances are, even think about. Bait stations are designed to keep bait away from pets and children, but they are also designed as little rat-friendly zones. With their small holes and zigzaggy interiors; bait stations are to a rat what a smoothly run fast-food restaurant is to a human. When rats eat the poisoned grain in the bait station, they return to their nests to die--in walls, in floors, underneath streets and restaurant stoves, in sewers. The most widely used poisons are anticoagulants, which cause the rat to bleed to death internally. It takes several meals for the rat to die. As it returns, it sometimes seems more and more woozy. Exterminators refer to this phenomenon as "dead rodent walking."
Ingesting poison, fighting for food, being attacked by a larger rat or beaten with a toilet plunger: these are everyday rat dangers that make the life expectancy of the rat in the city approximately one year. And yet rats persist; they thrive in New York City and in cities throughout the world. Rats do not inhabit cities exclusively, of course; like man, rats can live anywhere. Brown rats in wilderness areas are sometimes called feral rats; they survive on plants and insects and even swim to catch fish. However, brown rats are generally larger and more numerous in cities. As a result, it is in cities that they are especially successful at spreading the diseases that are like poisons to humans. They carry diseases that we know of and they may carry diseases that that we do not know of--in just the past century, rats have been responsible for the death of more than ten million people. Rats carry bacteria, viruses, protozoa, and fungi; they carry mites, fleas, lice, and ticks; rats spread trichinosis, tularemia, leptospirosis. They carry microbes up from the underground streams of sewage; public health specialists sometimes refer to rats as "germ elevators." Though targeted over and over by man; rats generally wreak havoc on food supplies, destroying or contaminating crops and stored foods everywhere. Some estimates suggest that as much as one third of the world's food supply is destroyed by rats.
Rats succeed while under constant siege because they have an astounding rate of reproduction. If they are not eating, then rats are usually having sex. Most likely, if you are in New York while you are reading this sentence or even in any other major city in America, then you are in proximity to two or more rats having sex. Male and female rats may have sex twenty times a day, and a male rat will have sex with as many female rats as possible--according to one report, a dominant male rat may mate with up to twenty female rats in just six hours. (Male rats exiled from their nest by more aggressive male rats will also live in all-male rat colonies and have sex with the other male rats.) The gestation period for a pregnant female rat is twenty-one days, the average litter between eight to ten pups. And a female rat can become pregnant immediately after giving birth. If there is a healthy amount of garbage for the rats to eat, then a female rat will produce up to twelve litters of twenty rats each a year. One rat's nest can turn into a rat colony of fifty rats in six months. One pair of rats has the potential of 15,000 descendants in a year. This is a lot of rats, and while the regenerative capabilities of the rat might seem incomparable to those of any other species, in Rats, Lice, and History, the classic work on the effect of disease on human history, Hans Zinsser suggests that the fertility rate of the human can rival the fertility rate of the rat.
>From Rats: Observations on the History and Habitat of the City's Most Unwanted Inhabitants. Chapter 1, pages 1-14. Copyright Robert Sullivan 2004. All rights reserved. No part of this book may be reproduced without written permission from the publisher, Bloomsbury.
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