The Super-Rats Are Coming

Wherever and whenever man moves, he takes with him an enemy--the rat. Sly, hardy and resilient, it rode with Marco Polo and voyaged with Magellan, Cabot and countless captains of tramp steamers. And like any ocean-bored traveler, the first thing a rat did was to get off the moment the ship docked.

To fight the rodents, the ancients used cats. Modern societies have tried potent poisons like strychnine and zinc phosphide. Trouble is, they not only kill rats but friendly animals and unwary human beings as well. In 1947, a better weapon appeared: an anticoagulant called warfarin. In small doses, it does not harm large animals. But when a rat swallowed it, it caused internal bleeding and death, usually within five days. For about 25 years, man felt he had the rat on the run. No more. British health authorities have discovered that brown "house" rats (Rattus norvegicus) in Wales and black "ship" rats (Rattus rattus) on Liverpool's docks now eat warfarin as casually as if it were an appetizer. Clearly a new immune strain has developed--the super-rat.

Specialists hoped that the new immunity would be confined to England. But last week the World Health Organization reported that immunity has been discovered in brown rats in Holland, Denmark, West Germany and the U.S. Said WHO: "The world is facing up to an international menace."

Catholic Tastes. That is putting it mildly. Rats and their parasites carry bubonic plague, murine typhus, trichinosis, leptospirosis and other diseases. Rats bite man in anger or nibble infants in hunger. Rats spoil an estimated 33 million tons of cereals each year, either by eating them outright or contaminating them with droppings. They steal eggs (whole), gnaw lazy elephants' feet and can kill young lambs.

What can be done to control super-rats? Cats unfortunately seem to have gone soft. To return to their murderous ways, they must be weaned from canned foods and retrained in what WHO calls "a suitable rat-killing environment" --one where other rat-hunting cats are at work. Snakes, mongooses and ferrets might help, if anyone wants such creatures around homes, docks and warehouses.

Incredible Cunning. Another way to kill rats is to return to the old poisons. With an almost incredible cunning, though, some rats have learned to let one member of the pack taste the bait. If he dies immediately, the food is ignored.

"We aren't exactly alarmed--the Ministry of Agriculture is never alarmed --but we are working very hard to find an alternative to warfarin," says a British government official. Even so, the rats have a final defense that has made a fool of man since the combat began. The average female produces up to twelve litters a year, and in each litter are ten ravenous young rats.

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