At Home - Bill Bryson [131]
Rat bites are almost certainly underreported because only the most serious cases attract attention, but even using the most conservative figures, at least fourteen thousand people in the United States are attacked by rats each year. Rats have very sharp teeth and can become aggressive if cornered, biting “savagely and blindly, in the manner of mad dogs,” in the words of one rat authority. A motivated rat can leap as high as three feet—high enough to be considerably unnerving if it is coming your way and is out of sorts.
The usual defense against rat outbreaks is poison. Poisons are often designed around the curious fact that rats cannot regurgitate, so they will retain poisons that other animals—pet dogs and cats, for instance—would quickly throw up. Anticoagulants are commonly used, too, but there is evidence to suggest that rats are developing resistance to them.
Rats are smart and often work cooperatively. At the former Gansevoort poultry market in Greenwich Village, New York, pest control authorities could not understand how rats were stealing eggs without breaking them, so one night an exterminator sat in hiding to watch. What he saw was that one rat would embrace an egg with all four legs, then roll over on his back. A second rat would then drag the first rat by its tail to their burrow, where they could share their prize in peace. In a similar manner workers at a packing plant discovered how sides of meat, hanging from hooks, were knocked to the floor and devoured night after night. An exterminator named Irving Billig watched and found that a swarm of rats formed a pyramid underneath a side of meat, and one rat scrambled to the top of the heap and leaped onto the meat from there. It then climbed to the top of the side of meat and gnawed its way through it around the hook until the meat dropped to the floor, at which point hundreds of waiting rats fell upon it.
When eating, rats will unhesitatingly gorge if plenty is available, but they can also get by on very little if necessary. An adult rat can survive on less than an ounce of food a day and as little as half an ounce of water. For pleasure they seem to enjoy gnawing on wires. Nobody knows why, because wires clearly are not nutritious and offer nothing in return except the very real prospect of a fatal shock. Still, rats can’t stop themselves. It is believed that as many as a quarter of all fires that can’t otherwise be explained may be attributed to rats chewing on wires.
When they are not eating, rats are likely to be having sex. Rats have a lot of sex—up to twenty times a day. If a male rat can’t find a female, he will happily—or at least willingly—find relief in a male. Female rats are robustly fecund. The average adult female Norway rat produces 35.7 offspring a year, in litters of 6 to 9 at a time. In the right conditions, however, a female rat can produce a new litter of up to 20 babies every three weeks. Theoretically, a pair of breeding rats could start a dynasty of 15,000 new rats in a year. That doesn’t happen in practice, because rats die a lot. Like a lot of other animals, they are more or less programmed by evolution to expire fairly easily. The annual mortality rate is 95 percent. A determined extermination campaign will normally reduce rat populations by 75 percent or so, but once the campaign stops the rat population will recover in six months or less. In short, an individual rat hasn’t got great prospects in life, but his family is effectively ineradicable.
Mostly, however, rats are just immensely lazy. They spend up to twenty hours a day asleep, normally emerging to look for food just after sunset. They seldom venture more than 150 feet if they can possibly help it. This may be part of a survival policy, for mortality rates rocket whenever they are compelled to migrate.
When rats are mentioned in a historical context, the one topic that invariably follows is plague. This may be not quite fair. For one thing, rats don’t actually infect us with plague. Rather, they harbor the fleas (that harbor