Rats - James Herbert - Macmillan Publishers

It was only when the bones of the first devoured victims were discovered that the true nature and power of these swarming black creatures with their razor sharp teeth and the taste for human blood began to be realized by a panic-stricken city. For millions of years, man and rats had been natural enemies. But now, for the first time—suddenly, shockingly, horribly—the balance of power had shifted.