Rattus norvegicus (Berkenhout, 1769)

Norway rat

The burrowing city rat, heavy, wary, and built for sewers and foundations.

Order: Rodentia
Family: Muridae
Group: Rodents
Ontario status: Established, urban

Why it matters

Contaminates food; gnaws structures and wiring; vector of leptospirosis and salmonellosis, and historically plague, via its fleas.

Origin

Native to northern China and Mongolia; spread worldwide with shipping, despite the name, it is not from Norway.

Behavior

Nocturnal; strongly neophobic, avoids new objects for days, unlike mice. Home range 15-30 m; an excellent swimmer and burrower.

Living conditions

Burrows along foundations, under debris, in sewers and basements. Needs daily water and 15-30 g of food; rarely travels far from the burrow.

Signs of presence

Blunt-ended droppings 12-18 mm near burrows and runs
Burrow openings ~8-10 cm along foundations and under debris
Greasy rub marks along walls and pipes
Gnaw marks ~4 mm wide on wood, plastic, and wiring

Weaknesses

Neophobia is predictable, it avoids new objects, so monitoring takes days to read
Burrow-bound: burrows along foundations reveal the whole colony
Needs daily water, removing water sources stresses the colony

Myths and facts

Myth A clean building can't have rats.
Reality Rats live in sewers and alleys, but a single broken drain or food spill sustains a colony. Sanitation lowers carrying capacity; it does not grant immunity.

Research notes

Morphology

Body 200-270 mm, tail 160-200 mm (shorter than head+body), weight 200-500 g. Blunt muzzle, small ears, thick scaly tail. Droppings 12-18 mm, capsule-shaped, blunt ends.

Diagnostics

Droppings blunt-ended and ≥12 mm; tail shorter than body; burrows rather than climbing. The blunt-vs-pointed droppings test separates it from roof rat.

Easily confused with

Roof rat (Rattus rattus) Roof rat: tail longer than body, pointed droppings 10-12 mm, climbs. Norway rat: tail shorter than body, blunt droppings 12-18 mm, burrows.
Muskrat (Ondatra zibethicus) Muskrat is semi-aquatic with a laterally flattened tail; rarely in structures.

Life cycle

Adult: Lifespan ~12 months in the wild; 2-3 years in captivity
Egg: N/A, viviparous
Egg to adult: Gestation 21-23 days; maturity at 8-12 weeks
Generations per year: 4-7 (year-round breeding indoors)
Nymph or larva: Pups weaned at ~21 days; sexually mature at 8-12 weeks

Development

Viviparous; altricial.

Reproduction

6-12 pups per litter × 4-7 litters/year.

Distribution

Global: Cosmopolitan
Native range: Northern China and Mongolia
Ontario: Established, the dominant urban rat province-wide

Ecology

Fossorial commensal; colonial burrow systems with dominance hierarchies; thigmotactic travel along walls, pipes, and edges; strong swimmers.

Resistance

VKORC1-mediated anticoagulant resistance documented in multiple populations worldwide, including North America.

IPM implications

Neophobia dictates monitoring duration, allow days of acclimation before reading results. Burrow mapping defines colony extent; exclusion targets burrow-adjacent entries; sanitation of food waste and standing water removes carrying capacity. Thigmotactic travel along walls and pipes dictates device placement.

Chemical ecology

Urine marking, plantar gland secretions, colony odor; pheromonal regulation of reproduction and hierarchy.

Genetics and DNA

Mammalian model organism, genome published 2004 (Rat Genome Sequencing Project Consortium, Nature).

Taxonomy

Order Rodentia › family Muridae › genus Rattus › R. norvegicus (Berkenhout, 1769). Also called the brown rat or sewer rat.

Open questions

VKORC1 resistance allele distribution across Ontario urban rat populations is unmapped.

References

UC IPM, Norway Rat (ipm.ucanr.edu)
Internet Center for Wildlife Damage Management, Norway Rat