norvegicus

Rattus norvegicus, commonly known as the brown rat or Norwegian rat, is a large rodent in the family Muridae. It is one of the most familiar rat species and is widely distributed around the world, particularly in urban and agricultural areas, where it often lives in close association with humans.

Taxonomy and identification. The species belongs to the genus Rattus. It is typically characterized by a robust body, brown to gray fur, small ears, and a blunt snout. Adults commonly measure about 20 to 25 centimeters in body length, with a tail of comparable length. Weights range from roughly 200 to 500 grams, depending on sex and environment.

Origin, distribution, and habitat. Rattus norvegicus is believed to have originated in northern China and parts of Asia and was spread globally through maritime trade starting in the early modern period. It thrives in a variety of habitats, including sewers, grain stores, fields, and buildings, where it forages for grains, fruits, and human food wastes.

Behavior and biology. This species is nocturnal, highly adaptable, and social, often living in colonies with complex social hierarchies. It is an omnivore with strong gnawing abilities and proficient swimming skills. Reproduction is prolific: females typically give birth after a gestation of about 21 to 23 days, producing litters that commonly contain 6 to 12 pups. Lifespan in the wild is short, usually under a year, while captives may live several years.

Impact and uses. Brown rats are major pests, linking to sanitation issues and agricultural damage, and they can transmit diseases to humans and domestic animals. They are also known as model organisms in scientific research and are widely kept as laboratory animals and, in some cases, as pets. Their genome has been sequenced, supporting extensive biomedical studies.