Earth Abides

That evening at home he sat down to it as a mathematical problem. With the aid of his father’s encyclopedia he determined that rats had approximately one litter a month, with an average of about ten young. That is, one month of uninterrupted breeding might have produced about a population of ten million rats in this given area. These young females, in turn, would begin to breed before they reached the age of two months. There must be some casualties, of course, and he had no way of determining just how many of the rats would live to maturity But, certainly the increase must be prodigious under the circumstances. His mathematics broke down.

But even if the rats should only be increasing at the rate of doubling their numbers every month, an estimate which seemed ridiculously conservative, there should by this time be already somewhere in the neighborhood of fifty million. If they were increasing threefold each month, an estimate which still seemed conservative, there would now be in the area approximately one billion rats.

As he considered the problem, he saw no reason at all why. the rats, with unlimited food, might not possibly quadruple their numbers every month. In the Old Times man had been the only important natural enemy of the city rats, and even man had had to maintain constant war against them to keep their numbers under control. With man gone, their only enemies would have been the small number of dogs whose instinct led them to catch rats, and somewhat larger number of cats. But here a secondary result must have influenced the situation in favor of the rats. As he had noticed, the rat-catching dogs seemed to hold the ground alone without the help of any cats. Probably the dogs had killed the cats as much as they had the rats, and so had eliminated the chief control. And in the end, the dogs themselves had probably been overwhelmed in the mere increase of numbers. Now he no longer saw any dogs. It seemed unlikely that they had actually been killed by the rats, although the rats may very well have cleaned out many litters of puppies. Probably, the dogs had merely retreated before the swarms of rats, and were still hanging around on the outskirts, now having been driven from the city into the suburbs.

Whether there were a billion rats or only fifty million made very little difference. There certainly were too many rats, and Ish and Em felt themselves in a state of siege. They watched all the doors carefully. Nevertheless, one rat appeared in the kitchen from some unknown quarter, and they had a mad scurry as Ish pursued it with a broom. Cornered, it leaped viciously at the broom-handle, and left teeth marks in the hard wood before he was able to crush it against the floor.

After a few days, moreover, they began to see a kind of difference, both in the appearance and in the behavior of the rats. Apparently, the supplies of food, vast though they were, had at last begun to yield before the attack of an ever-pyramiding number of rats. The rats now appeared thinner, and they ran around even more feverishly in search of food. They began to burrow in the ground. They dug up the tulip bulbs, first of all, seeming particularly fond of them. Then they attacked the less palatable bulbs and roots. They ran along the branches of the trees, apparently eating any insects they could find or any remains of seeds or fruit. They even, at last, began to gnaw the bark of young trees, like rabbits.

Ish parked the car as close to the house as he could now, and made a dash for it, wearing high boots. But actually the rats never made any attempt at an attack. Ish kept Princess in the house mostly, although the rats had offered her no violence either.