Norway Rat

The Norway rat, Rattus norvegicus, belongs to the family Muridae. Adults typically measure 25–40 cm in total length, including a tail shorter than the body, and weigh 200–500 grams, though exceptional specimens can exceed 600 grams. Their fur is coarse, brownish-grey dorsally and grey-white ventrally, with distinguishing small ears, a blunt snout, and a scaly, sparsely haired tail. Gestation lasts approximately 21–23 days, with females producing 5–7 litters annually, each comprising 6–12 pups that are altricial at birth. Sexual maturity is reached rapidly, often within 8–12 weeks under optimal conditions, and their maximum lifespan in the wild is 1–2 years, though usually less due to predation and control efforts. They thrive in temperate climates, preferring temperatures between 15–25°C and high humidity.

Norway rats are primarily nocturnal, exhibiting crepuscular activity spikes at dusk and dawn. They are highly social, living in colonies with complex hierarchies, and communicate using a variety of vocalizations, tactile signals, and olfactory cues, including pheromones for reproductive and territorial marking. Dispersal typically occurs over short distances, with young males traveling further from the natal nest. Their diet is omnivorous and opportunistic, consuming grains, meats, fruits, and refuse, often caching food. When threatened, they can be aggressive, biting and scratching, particularly females defending litters. Their incessant gnawing behavior poses significant structural risks, damaging electrical wiring—a leading cause of electrical fires—and undermining foundations, alongside their role as vectors for numerous pathogens including Leptospira, Salmonella, Hantavirus, and Yersinia pestis (indirectly, via fleas).