Robert Sullivan is the author of numerous books, including "Rats: Observations on the City and It's Most Unwanted Inhabitants" and, most recently, "My American Revolution: Crossing the Delaware and I-78," a look at the relationship between the ecology of New York and its Revolutionary War history.

...An exciting rat "fact" that is not true at all, despite how often it is quoted, is that there are 8 million rats in New York, one per person. You hear it all the time—when a rat is YouTubed on a subway or in a Taco Bell, or more significantly (if less likely to be covered) when Mayor Bloomberg cuts the number of workers who might be sent into a neighborhood to take care of a rodent infestation. You will likely hear it at some point this week, or at least some wild, unverifiable number.  This stat was disproved first and forever in 1949 by David E. Davis, a biologist from Johns Hopkins University who is the founding father of rat ecology, as well as urban ecology. Davis trapped rats throughout New York and estimated 250,000 rats, or one for every 36 people. But then the UN began quoting the one-rat-per-person statistic again, and within a short time, the city itself began quoting it. (When I published the history of the statistic in a New York Times Magazine piece in 2004, debunking it, the Times published a letter from a reader shortly thereafter, debunking me, citing a Joseph Mitchell story from 1944.) We despise it and we love it for what it purports to say about us, and the untrue fact, like a tough rat, survives.

Dave Davis’ work was pioneering in that he looked at cities as ecosystems. His work was sponsored by the federal government, concerned about food stores donated to a devastated Europe under the Marshall Plan. Prior to Davis, there was little hard science on what rats ate and how they lived in the urban environment, and little consideration of the ecology of cities. Today we have studies on how rats transmit various diseases, such as leptospirosis, hanta virus, and, in very rare cases, the plague. And we know that after a flood event, the water itself—contaminated with raw sewage, as well as petroleum products and all the not-as-terrifying pollutants that normally cover our streets—is potentially more of an issue in terms of spreading pathogens than rats. (After Irene and even Katrina, outbreaks of rat-associated viruses did not occur.) Again, sewer treatment plants in low-lying areas, tend not to be in high-income neighborhoods....

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