Rattus rattus (Linnaeus, 1758)

Roof rat

The climbing rat, arboreal, agile, and at home in attics and rafters.

Order: Rodentia
Family: Muridae
Group: Rodents
Ontario status: Sporadic in Ontario, less cold-hardy than Norway rat

Why it matters

Contaminates stored food; damages structures and wiring in attics; the historical plague rat of medieval Europe.

Origin

Native to South and Southeast Asia; spread worldwide on ships, the classic ship rat of port cities.

Behavior

Nocturnal; arboreal and acrobatic. Less neophobic than the Norway rat, investigates new things sooner. An excellent climber.

Living conditions

Nests high: attics, rafters, trees, dense vines, and upper floors. Follows wires, branches, and fences as aerial highways.

Signs of presence

Pointed droppings 10-12 mm in attics and along rafters
Gnawed fruit, nuts, and pet food in elevated areas
Nests of shredded material in attics and dense vegetation
Nocturnal scurrying overhead

Weaknesses

Arboreal habit concentrates signs in attics, inspect upward, not downward
Less neophobic than Norway rats, so monitoring reads faster
Cold-sensitive: Ontario winters limit its outdoor survival

Myths and facts

Myth Roof rats and Norway rats are the same animal.
Reality Different species, different habits: roof rats climb and nest high; Norway rats burrow and nest low. Tail longer than body = roof rat; shorter = Norway rat.

Research notes

Morphology

Body 160-200 mm, tail 190-250 mm (longer than head+body), weight 150-250 g. Sleek build, pointed muzzle, large ears. Droppings 10-12 mm, pointed or banana-shaped ends.

Diagnostics

Tail longer than body + pointed droppings 10-12 mm + elevated nesting sign. Sleeker and lighter than Norway rat at every age.

Easily confused with

Norway rat (Rattus norvegicus) Norway rat is heavier with a blunt muzzle, tail shorter than body, and blunt droppings 12-18 mm.

Life cycle

Adult: Lifespan ~12 months in the wild
Egg: N/A, viviparous
Egg to adult: Gestation 21-23 days; maturity at 8-12 weeks
Generations per year: 4-6 (year-round in heated structures)
Nymph or larva: Pups weaned at ~21-28 days; mature at 8-12 weeks

Development

Viviparous; altricial.

Reproduction

6-8 pups per litter × 4-6 litters/year.

Distribution

Global: Cosmopolitan in warm regions; displaced by Norway rat in many temperate cities
Native range: South and Southeast Asia
Ontario: Sporadic, less cold-hardy than Norway rat; mostly port cities and heated structures

Ecology

Arboreal commensal; nests above ground in vegetation and structures; uses linear features (wires, limbs, fences) as travel routes; frugivorous tendency.

Resistance

Anticoagulant resistance documented in some populations globally; Ontario status unknown.

IPM implications

Inspection goes vertical: attics, rooflines, and tree limbs touching structures. Trim vegetation bridges; seal roofline gaps. Arboreal travel routes, wires, branches, vines, are the monitoring lines, not floor perimeters.

Chemical ecology

Urine and plantar-gland marking along aerial runways; colony scent at nest sites.

Genetics and DNA

Reference genome published: Rrattus_CSIRO_v1 (NCBI RefSeq Release 100); de novo assembly in Yu et al. 2022, Nature Communications.

Taxonomy

Order Rodentia › family Muridae › genus Rattus › R. rattus (Linnaeus, 1758). Also called the black rat or ship rat.

Open questions

Northern range limits in Ontario under warming winters are undocumented.

References

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