The brown rat (Rattus norvegicus)

The brown rat (Rattus norvegicus), also known as the Norway rat or common rat, is one of the most widespread and adaptable rodent species in the world. Originating from northern China, this species has successfully colonized nearly every corner of the globe, often thriving in close association with human settlements.

Brown rats are robust rodents with a heavy, thickset body and a blunt nose. They typically measure between 20 to 25 centimetres (8 to 10 inches) in body length, with an additional tail length of 18 to 25 centimetres (7 to 10 inches). They weigh between 200 to 500 grams (7 to 17.5 ounces). Their fur is coarse and primarily brown or grey on the back and lighter on the underside. Their ears and tail are noticeably scaly and sparsely furred.

Brown rats are highly adaptable and omnivorous, consuming a wide variety of foods, although they prefer grains and seeds. They are primarily nocturnal creatures, displaying high levels of activity during the night. Known for their impressive burrowing ability, brown rats construct extensive underground networks where they live in colonies. They are also proficient swimmers and climbers, which aids in their ability to invade diverse environments.

Brown rats have a remarkable reproductive rate. Females can become sexually mature as early as five weeks old and are capable of producing up to 12 litters per year, with each litter containing 6 to 12 pups. This rapid reproduction contributes to their ability to swiftly colonize new areas and maintain high population densities.

Often considered pests, brown rats can cause significant damage to crops, food stores, and infrastructure due to their gnawing habits. They are also vectors for various diseases, such as leptospirosis, salmonellosis, and hantavirus, posing a public health risk. Despite their negative impacts, they have also contributed to scientific research, especially as the primary species used in laboratory experiments due to their physiological and genetic similarities to humans.

Brown rats are highly versatile in their habitat preferences. They are commonly found in urban environments, such as sewers, basements, and alleyways, but they also inhabit rural areas, living in fields, farms, and forests. Their adaptability to different environments is a key factor in their global distribution.