The word mice or mouse is sometimes used to refer to any small rodent. The word mouse has no exact meaning in classification systems. There are numerous amounts of mice in the world, but for convenience they are often grouped as the Eurasian mice and the American mice. Most mice live in human habitats. Most, but not all, of the rodents called mice are members of the rodent subclass Myomorpha, meaning mouse like rodents. There are around 1,100 species in this group and are classified in several different families. Other types of mice include: the European harvest mouse, the African tree mouse, the deer mouse, the American harvest mouse, the grasshopper mouse, the South American field mouse, pack rats, and rice rats. Other rodents that resemble mice are the mole, hamster, lemming, muskrat, and the gerbil. There is a marsupial mouse, but it is not a rodent descendant, but instead a kangaroo ancestor. .
Mice are common and are indigenous to almost every land area. They eat various foods, including grain, roots, fruit, grass, insects, and sometimes human food. Many mice species prefer to live in man made structures because they are a lot more stable and warm. Mice can be huge pests because they destroy food, gnaw on all types of materials, and sometimes carry diseases such as murine typhus and plagues. Some mice in the wild become so numerous that they become permanent crop pests and kill the farmer's crops uncontrollably. Mice although do benefit humans by being a food supply for larger animals that could instead be harming livestock and large amounts of agriculture. Some mice problems might even result in the exterminator having to come and kill the mice off, but usually getting rid of mice can be taken care of by using mouse traps. .
The house mouse, Mus musculus, mostly encountered in buildings, has been brought over by humans from Eurasia to all inhabited areas in the world. These mice are brown or gray, and can grow up to twenty cm.
