The only good thing that can be said for rats is that they get up a lot of rubbish, especially bad meat and other kinds of food that would cause disease if left about. But rats make up for any good they may do in this way by the amount of good food they devour, and by the diseases, they bring to men. Rats are great thieves, and they destroy every year large amounts of grain and human food of every kind. And as their numbers increase very quickly, if they were not kept down they would swarm in such numbers as to destroy all the food, and even drive people out of their villages and towns. So men are always at war with rats, and yet the rats still swarm.
In India, rats are especially dangerous because they carry the plaque flea, whose bite gives people the dreadful disease called plague. If rats increase in great numbers in any place and are not driven out of people’s houses, the people are sooner or later attacked by the plague, which may spread rapidly all over a whole province and cause thousands of deaths. The only way to keep the plague away is to kill the rats which bring it.
Rats live in villages and towns because there they can find such a lot of food. They hide in holes, drains, and dark cellars under the houses, and come out at night to steal. There are different ways of catching and killing them. Cats and certain kinds of dogs are good rat-catchers and can be trained to catch and kill. Rats are also caught in traps baited with cheese, fat, or meat. And they are often killed in large numbers by poisoned meat placed near their holes.
Every ship carries hundreds of rats, who hide in the hold and eat any food they can find. This is the way rats have been spread all over the world. It is thought that rats first came from China; but now men have, without wanting to do so, carried them to Europe and America, and every country, where they have become a pest and a danger.