On the one hand they form a vital link in the food chain for larger animals, both mammalian and reptilian. Without the abundance of mice and rats, some animals would undoubtedly turn their unwelcome attentions onto more domestic creatures. On the other they cause huge damage to standing crops, stored food and any structure that they can gnaw through, as well as leaving their excreta in places of food storage. It seems no coincidence that the worship or cults of snakes and cats arose in Egypt and India, the two ancient societies that had most to fear from the depredations of rodents.
Rodents are also a fantastically successful order.
Like the lizards, they have spread out across the world and radiated into practically every part of the globe except the poles. Indeed, they have been around in one form or another since the demise of the larger, mammal-like reptiles between the Permian and Triassic eras. It was rodent-like creatures that kept the mammal torch burning during the formidable Age of the Dinosaurs, whereas cats, dogs and rabbits are comparative newcomers. Finally, the primates are supposedly descended from rodents, an interesting path that leads from small shrew-like beings to man himself. It seems an interesting aspect of man's personality that the creatures he often fears or despises he nevertheless sometimes takes as a companion, and rats in particular have become well-established as pets as well as vermin.