Found a dead rat in my yard yesterday. Now I must live with the reality that there are .... others.

Chemicals developed in the middle of the 20th century raised hopes that perhaps technology could vanquish the rat. But rats are cautious — neophobic, is the technical term. They’re so wary of new things in their environment that experienced exterminators leave traps unset for days, letting rats become accustomed to eating from them. Modern anticoagulant poison is designed to be slow-acting, bursting the rodent’s capillaries days after ingestion, so that other rats won’t associate the bait with death.

The problem is that rats breed too quickly for poison to make much difference. The Norway rat has a three-week gestation period and can produce five litters a year, each with four to eight offspring. In as few as three months, those rats can produce litters of their own. In theory, a single pair is capable of giving rise to thousands of progeny in under a year.

Last week, the story of a British tortoise that lost its front leg after rats gnawed them off circulated widely.

So, we kill them as fast as we can. We kill rats because they eat our food and defecate in whatever they don’t eat. They once caused famines, though in modern agriculture they’ve been reduced to a nuisance — the FDA publishes limits of acceptable "rodent filth" per gram.

We kill rats because they’re reservoirs of disease, including plague*, which wiped out 60 percent of Europe’s population in the 14th century and for which we’ve never forgiven them. They swarm with other diseases as well: a recent study of rats caught in New York City found pathogens proven to cause salmonella,E. coli, hantavirus, and Leptospira, as well as 18 previously unknown viruses.

We kill rats because they destroy the things we build: they gnaw on wires, starting fires, and gas lines, causing explosions. Their burrows collapse streets and sidewalks. Today, some of the most aggressive rat control projects are carried out by ecologists, trying to kill rats before rats kill native fauna. Every era hates rats in its own way.

We hate rats because they thrive in the places we try to forget: sewers, empty lots, derelict buildings, mountainous landfills. "Rats live in man’s parallel universe, surviving on the effluvia of human society," writes Robert Sullivan in his book Rats. When they scurry onto the subway platform or pop out of our toilets — an urban legend that’s all too true — it’s like a furry little return of the repressed. They’re ambassadors of entropy, appearing in huge numbers during floods, wars, economic decline, or other periods of disorder. All of that is captured in a pervasive feeling: rats are gross.

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The rat’s future looks bright. Trade is accelerating, and cities are expanding as their infrastructure decays. But in a few places, people are bringing new tactics and technology to the war on rats. Scientists, city planners, exterminators, engineers, pilots, and ordinary citizens are all enlisted in these new campaigns, which offer hope of finally pushing back the rat, at least for a while.

If there’s a constant in the history of rat control, it’s the sense that there must be a better way. An early 20th century Department of Agriculture report is florid in its despair: "For centuries the animal has been banned, and human ingenuity has been taxed to the utmost to suppress it," wrote David E. Lantz. "Everywhere the history of the contest is the same. Though thousands are killed, the relief is only temporary, and other thousands soon replace the slain. Therefore, if conducted along the old lines, the war promises to be never-ending."

* Gerbils, not rats!  http://pandawhale.com/post/59006/rats-exonerated-in-spread-of-black-death-gerbils-implicated

We believe in the interconnectedness of all things.

Perhaps the rats serve a higher purpose.

...or we're embroiled in a life-and-death battle for the survival of our species!