for National Geographic News
It is a widespread and very popular belief, that however obnoxious an animal parasite may be, it has some compensatory feature attached to its existence; that in nature's scheme of affairs it fulfills some useful purpose.
A thoughtful consideration of the rat, however, fails to reveal any redeeming feature that could justify a tolerance of this highly destructive and disease-bearing pest. Perhaps in other ages and under different sanitary conditions than now exist in civilized communities the rat served as a much needed scavenger; but changing conditions have robbed the rat of even this questionable argument for existence.
A lot of things have changed since June 1919, when New Haven, Connecticut, health authorities issued these comments. But common attitudes about the rat have not.
Rats are among nature's most prolific mammalian breeders. Female rats breed up to a dozen times in a year and produce, on average, a half-dozen offspring. Some litters total 20 or more. It's estimated that the United States alone could house 150 million rats, possibly more.
To be fair, rats have made an incomparable contribution to laboratory sciences.
But when living in large numbers in close proximity to humans, the rodents take an enormous economic bite on people. They can devastate crops, food stores, and wreck havoc on buildings. Such property damage can tally billions of dollars.
Beyond such economic damage, however, rats pose health hazards. The animals harbor the lice and fleas that spawn serious diseases such as typhus, trichinosis, and infectious jaundice. In the past they've also taken the rap for outbreaks of plaguesuch as the catastrophic Great Plague in 17th-century London.
And attacks on humans aren't out of the picture either. (Those who recall the mass rat-on-human attacks from the original 1971 Hollywood horror film Willard should note that such scenes were made possible by actors covered in peanut-butter.)
Brown rat, house rat, barn rat, wharf rat, by any of these names the rat is the same common species: the Norway rat (Rattus norvegicus). The rodent, which grows from 12.5 to 19 inches (32 to 48 centimeters) long from nose to tail, is one of nature's most resourceful, adaptive creatures. Its diet is more varied than any other mammal, and its close relationship to humans means that Norway rats have managed to appear most everywhere that people dowhether we like it or not.
The average rat can wriggle through a hole the size of a quarter, scale a brick wall, tread water for several days, gnaw through lead pipes and cinder blocks, survive a five-story fall, survive being flushed down a toiletand even enter a building through the same route.
It's an impressive resume for an indefatigable animal. So are we destined to live forever with rats? It would seem so, but perhaps not everywhere. In the Canadian province of Alberta, a 50-year battle has succeeded in keeping the province rat free. But it's not an easy task. To deter such a resourceful animal requires eternal vigilance.
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