Rodents (from Latin rodere, “to gnaw”) are mammals of the order Rodentia, which are characterized by a single pair of unremittingly growing incisors in each of the upper and lower jaws. About forty percent of all mammal species are rodents; they are found in vast numbers on all continents except Antarctica. They are the most diversified mammalian order and live in a variety of terrestrial habitats, including human-made environments. There are species that are arboreal, fossorial (burrowing), and semiaquatic. Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, hamsters, and capybaras. Other animals such as rabbits, hares and pikas were once included with them, but are now considered to be in a separate order, Lagomorpha.
Most rodents are small animals with robust bodies, short limbs and long tails. They use their sharp incisors to gnaw food, excavate burrows and defend themselves. Most eat seeds or other plant material, but some have more varied diets. They tend to be social animals and many species live in societies with complex ways of communicating with each other. Mating among rodents can vary from monogamy, to polygyny, to promiscuity. Many have litters of underdeveloped, altricial young, while others have precocial young that are relatively well developed at birth.
The rodent fossil record dates back to the Paleocene on the supercontinent of Laurasia. They greatly diversified in the Eocene, as they spread across continents, sometimes even finding means to cross oceans. Rodents reached both South America and Madagascar from Africa, and were the only terrestrial placental mammals to reach and colonize Australia.
Rodents have been used as food, for clothing, as pets and as laboratory animals in research. Some species, in particular the brown rat, the black rat, and the house mouse are serious pests, eating and spoiling food stored by humans, and spreading diseases. Accidentally introduced species of rodents are often considered to be invasive, as they sometimes threaten the survival of native species, such as island birds, previously isolated from land-based predators.
The deer mouse is found in rural areas and rarely invades residential homes. Deer mice are of medical concern because they are common carriers of Hantavirus.
The house mouse is the most common rodent pest in most parts of the world. It can breed rapidly and adapt quickly to changing conditions. In fact, a female house mouse can give birth to a half dozen babies every three weeks, and can produce up to 35 young per year.
Norway rats are believed to be of Asian origin, but are now found throughout the world. These rats can cause damage to properties and structures through their gnawing. Norway rats have smaller eyes and ears and shorter tails.
What are roof rats? Roof rats – also called black rats or ship rats – are smaller than Norway rats, but cause similar issues. This rodent gets its name from its tendency to be found in the upper parts of buildings. The roof rat is thought to be of Southeast Asian origin, but is now found throughout the world, especially in tropical regions.