The brown Norway rat (Rattus norvegicus) is a highly adaptable and widely distributed rodent. It has established populations across nearly all continents, thriving in diverse environments. Recognized for its intelligence and resilience, this species is pervasive globally. While often associated with human settlements, its natural history reveals a complex biology.
Physical Traits and Global Presence
The brown Norway rat is a robust rodent, weighing between 140 to 500 grams, with some individuals reaching up to 900 grams in domestic settings. Its body length ranges from 15 to 28 centimeters, and its tail is shorter than its head and body combined, measuring 10.5 to 24 centimeters. The fur is coarse, predominantly brown or dark grey on the upper side, transitioning to a lighter grey or brown on the underside.
The species originated in the plains of northern China and neighboring areas. From there, it spread globally, reaching Europe in the Middle Ages and North America around the mid-1700s, often as stowaways on ships. Today, brown rats are found on every continent except Antarctica, making them the dominant rat species in many parts of Europe and North America. They exhibit adaptability, inhabiting a wide range of environments from urban areas like sewers and buildings to agricultural lands, forests, and open fields, often preferring locations near human activity where food and shelter are readily available.
Behavior and Lifestyle
Brown Norway rats are nocturnal, active around dusk to forage for food and water. They possess acute senses of hearing, smell, and touch, which they rely on due to their poor eyesight. These rats are skilled diggers, constructing burrow systems that include chambers for food storage and nesting.
They are omnivorous, consuming diverse food sources, which has contributed to their global success. In urban settings, their diet consists of discarded human food, while in natural environments, they eat plants, insects, and small vertebrates like fish, lizards, chicks, and other rodents. Brown rats live in hierarchical social groups, with males dominating. Females can breed throughout the year if conditions are favorable, producing multiple litters annually, with gestation periods lasting 21 to 23 days and litter sizes averaging seven to fourteen pups.
Significance to Humans and Science
The brown Norway rat holds dual significance for humans, acting as both a common pest and an important scientific model. As a synanthropic species, it thrives in association with human environments, inhabiting urban areas, agricultural lands, and homes. This proximity can lead to property damage, contamination of food supplies, and the transmission of various pathogens, including bacteria and parasites. Wild brown rat populations have been linked to outbreaks of diseases like trichinosis and can carry bacteria such as Coxiella burnetii, which causes Q fever.
Conversely, the brown Norway rat has become a valuable model organism in scientific research, particularly the domesticated subspecies Rattus norvegicus domestica, known as the laboratory rat. Its physiological similarities to humans make it suitable for studies in genetics, neuroscience, toxicology, and drug development. Researchers utilize rats to investigate complex traits and diseases, with their larger body size allowing for more sophisticated physiological measurements and surgical manipulations compared to smaller models like mice. The sequencing of the Brown Norway rat genome has enhanced its utility, providing insights into mammalian evolution and the genetic basis of human diseases.