Living Organisms / Animalia / Craniata / Mammalia / Rodentia / Muridae / Rattus / Species
Rattus norvegicus - Brown rat (Click photographs/illustrations: full picture & further details)
Click Photo for full-page view Click Photo for full-page view Click Photo for full-page view Click Photo for full-page view








Return to top of page

General and References

Alternative Names (Synonyms)

  • Norway Rat
  • Common Rat
  • Rat d'egout (French)
  • Surmulot (French)
  • Rat surmulot (French)
  • Wanderratte (German)

Names for new-borns / juveniles

Names for males  
Names for females  

Return to top of page

General Appearance

Typical rat with pointed muzzle, large eyes, large ears and long naked tail (D30)

Similar Species

  • Distinguished from Rattus rattus - Roof rat by: smaller and haired ears, paler overall colouring and shorter, thicker bicoloured tail (B142, D30)
  • Distinguished from mice, voles and squirrels by: size, relatively pointed muzzle and long scaly tail; compared with Arvicola terrestris - Water vole, muzzle is more pointed, ears larger and tail longer (B142).
Sexual Dimorphism Sexes similar. Males generally larger than females (B142).

Return to top of page


Species Author

Debra Bourne

Major References

Husbandry references:
B142, B169.24.w24

Other References

Click image for main Reference Section

Return to top of page

TAXA Group (where information has been collated for an entire group on a modular basis)

Parent Group

  • Rats (Rodents)

Specific Needs Group referenced in Management Techniques

  • Rats (Rodents)

Return to top of page

Husbandry Information


  • Unlike domestic and laboratory rats, even hand-reared wild rats become nervous and difficult to handle from an early age (B142).
  • Wild rodents may carry diseases transmissible to humans. Care should be taken in all handling of wild rodents. B169.24.w24
  • Wild rodents are liable to bite. B169.24.w24
  • Wild rodents are generally less stressed by indirect (e.g. being tipped gently from one container into another) than direct handling. B169.24.w24
  • Wild rodents are less stressed if handled in reduced light conditions (B169.24.w24).
  • Wild rats should be considered dangerous and never handled directly without being anaesthetised. (B169.24.w24)
  • Transfer from one cage to another may be carried out without direct contact, by quietly allowing the rat to move from the container into a strong black cloth bag, and then encouraging it out of the bag into the other container. (B169.24.w24)
  • The cloth bag should be secured tightly e.g. with a rubber band while being carried. B169.24.w24

Accommodation: wild rats will quickly chew through plastic laboratory cages. Stainless steel mesh cages (29cm x 35cm x 25cm high for an individual rat) are used for laboratory housing of wild rats, with a metal hideaway clipped onto the back of the cage and shredded paper (replaced 2-3 times a week) for bedding/concealment (B169.24.w24).


  • CO2/O2 until loss of consciousness, then increase CO2 to 100% and keep there for at least 10 minutes. N.B. neonatal rats and mice are relatively resistant to CO2.
  • Stunning
  • Decapitation
  • Lethal dose of inhalation anaesthetic e.g. halothane (B169.24.w24).

Management Techniques


Return to top of page

Appearance / Morphology

Measurement & Weight

Length Head-body length: up to 280mm (B142, D30)

Tail: 80-100% of head-body length (B142)

Hind foot: 40-44mm (B142).

Ear: 20-22mm (B142)

Height --
Adult weight General 500g, maximum recorded 794g (B142); usually 200-400g, few to 500g (B147).
Male --
Female --
New-born weight 5-7g (B147).
Growth rate 110mm and 40g at weaning (B142).

Return to top of page


General --

Skull: Larger, heavier and more angular than skull of Rattus rattus  - Roof rat. May reach 54mm condylobasilar length (B142).

Nose: relatively pointed

Ears: 20-22mm long, haired.

(B142, D30)

Dentition (Teeth) --
Eyes Large, dark (B142, D30)

Return to top of page

Legs and Tracks

Hind feet 40-44mm (B142)

Return to top of page


Length just less than head-body length (80-100%). Dorsal surface dark,ventral surface lighter (B142, D30).

Return to top of page

Coat / Pelage

Adult Female Shaggy. variable colouration.
  • Dorsal: grey-brown.
  • Ventral: pale grey.
  • Tail: dorsal sparse, dark and ventral sparse pale

(B142, D30)

Variations (If present)
  • Melanic: - common in some populations, e.g. 1-2% of London population.
  • Albino: rare.
  • Ventral: white stripe or blaze.


Moult --
New-born / Juvenile Juveniles to three months fur shorter, sleeker, greyer (B142)

Return to top of page

Neonate (New-born) Characteristics

Altricial: naked and blind (B142, B147).

Return to top of page

Detailed Anatomy Notes
(Summary information provided for pertinent species-specific data cross-referenced in Wildpro)

Reproductive: Six pairs of nipples (B142).

Return to top of page

Life Stages / Natural Diet / Physiology.

Reproductive Stages

Breeding Season May be all year if food available. Other habitats mainly summer and autumn (B142).

Usually spring and autumn peaks but some populations all year (B147).

Oestrus / Ovulation
  • Often post-partum oestrus within 18 hours of birth. (B142, B147).
  • Polyoestrus (B147)
  • Oestrus cycle 4-6 days, oestrus lasts 20 hours (B147)
Gestation / Pregnancy 21-24 days (B142); 21-16 days (B147)
Parturition / Birth --
Neonatal development
  • Birth: naked, blind
  • Six days: eyes open
  • Three weeks: weaned 
  • (B142)

15 days: eyes open, fully furred; 22 days: weaned, leave nest (B147).

Litter size
  • Varies with size of mother: average 7-8, 500g female may produce 11 but 150g female only 6 (B142).
  • 2 to 22, average 8-9 (B147).
Time between Litters / Litters per year
  • Usually up to five litters per year, rarely more (B142).
  • 1-12 litters per year (B147).
Lactation / Milk Production
  • Three weeks (B142).
Sexual Maturity
  • Females by about 11 weeks (115g). (B142); 2-3 months (B147).
  • Usually one to two years (B142).

Return to top of page

Natural Diet

  • Omnivorous.
  • Starch-rich and protein-rich foods prefered, e.g. cereals.
  • Meat, fish, bones etc. may be eaten in urban environments.
  • Cereals and root crops but also e.g. brassicas in agricultural areas.
  • Also earthworms, rice grass and crustaceans on sea shores, molluscs by rivers.

(B142, B147).

Return to top of page

Detailed Physiology Notes
(Summary information provided for pertinent species-specific data cross-referenced in Wildpro)

Temperature --
Pulse --
Respiration --
Faeces Coarse-textured, about 12mm long, may be tapered at ends, often deposited in groups (B142).
Haematology / Biochemistry --
Chromosomes 2n = 42, FNa = 62 (B142).
Other --

Return to top of page


Feeding Behaviour

  • Opportunist.
  • May carry food to safe place before eating.
  • Sometimes hold food in forepaws while eating.
  • Hoard food.
  • New sources of food approached cautiously and initially only sampled


Return to top of page

Parental Behaviour


Return to top of page

Social Behaviour / Territoriality

  • Colonies made up of aggregations of smaller 'clans'.
  • Clans may be pair or male and several females defending a territory.
  • Home range and movement depends on food availability.
  • Females range less widely and defend smaller territories than males.
  • Aggression shown to strangers entering a colony.
  • Aggression within colony increases as population density increases.
  • Injuries on rump from aggressive encounters.


Inter-specific --

Return to top of page

Sexual Behaviour

  • High ranking males male with several resident females and exclude other males (B147)..
  • Within packs of low-ranking animals, oestrus female followed by numerous males and mounted repeatedly (B147).

Return to top of page

Predation in Wild

Most predators including foxes, cats, owls, but mainly juveniles taken (B142).

Return to top of page

Activity Patterns

  • Urban areas: no obvious seasonal rhythm (B142).
  • Agricultural: transient rats in summer and autumn - displaced males. Increased population on farm premises in winter (B142).
  • Fast trot along familiar runs, also slower amble while searching for food.
  • Swim well, dive well.
  • Climb in buildings; rarely climb trees.
  • Dig burrows.

B142, B143.

Circadian --

Return to top of page

Habitat and Range

General Habitat Type

  • Urban and rural habitats - widespread (D30).
  • Adaptable, versatile. 
  • Use habitats where no or few competitors or where human activity increases food supple.
  • Farms, refuse tips, sewers, urban waterways, warehouses, also around cereal and root crops.
  • Areas with dense ground cover preferred.
  • Areas close to water preferred.
  • Use lower, damp areas of buildings.

(B142, B147)

Return to top of page

Nests / Burrows / Shelters

  • Usually below ground. 
  • Also use straw bales, or nest among sacks.
  • Burrows are usually 6-9cm diameter, often on sloping ground or under cover such as tree roots, flat stones. Dug earth remains as heap near entrance.
  • (B142).

Return to top of page

Distribution and Movement (Migration etc.)

Normal Native to north-east Asia (northern China) (B143, B147); probably originally south-east Asia (B51)
Occasional and Accidental --
Introduced Now worldwide (tropics and warm temperate) as human commensal (B51, B147); worldwide in urban areas except mainland low altitude inland towns in tropics and subtropics. Found both in cultivated areas and areas away from humans, in temperate areas and tropical islands with few indiginous competitors (B142).
  • In Europe: widespread but less in Mediterranean than further north, and sporadic in sparsely-populated areas of Fennoscandia (B143)
  • Britain: introduced in the first half of the 18th century; found everywhere except very exposed mountain areas and some small offshore islands (B142, B221)

Return to top of page


Intraspecific variation

Two subspecies:
  • Rattus norvegicus norvegicus
  • Rattus norvegicus caraco (Pallas, 1779) (in Asia).


Return to top of page

Conservation Status

Wild Population -
  • Common. Generally considered a pest. (B143)

  • In Britain: common. Pre-breeding population estimate of about 6,790,000, including 5,240,000 in England, 870,000 in Scotland, 680,000 in Wales. Population estimate was "based on a very limited amount of information for the species" although additional knowledge "may not necessarily have made a substantial difference to the estimate". Population estimates considered minimums (B221)

General Legislation --
CITES listing --
Red-data book listing --
  • Locally, improved environmental hygiene and intensive rat control measures (B221).
Captive Populations --
Trade --

Return to top of page