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Rattus rattushouse rat(Also: black rat; roof rat; ship rat)

By Heather Gillespie

Geographic Range

Rattus rattus, is found on all continents of the earth. Although the species is believed to be native to India and possibly other Indo-Malayan countries, it has been introduced through human travel overseas to all continents. It is most common in coastal areas because it is a rodent that flourishes in areas inhabited by humans as well as on large ships. For this reason, these animals are often called ship rats. Some other common names for this species include house rat, black rat, and roof rat. Rattus rattus thrives in tropical regions but has been largely driven out of more temperate regions by Noway rats, R. norvegicus. Norway rats, are closely related to black rats, but are more successful in colder climates. However, some data show that R. rattus has been able to adapt to more extreme cold and harsh climate conditions. (Grzimek, 2003; Grzimek, 2003; Pye, Swain, and Seppelt, 1999)

Habitat

Rattus rattus is most often found in large numbers in coastal areas because of the way the species is spread through human sea faring. It is generally found in any area that can support its mainly vegetarian diet. Because R. rattus is an agile climber, it often lives in high places, such as top floors of buildings in populated areas or trees in forested areas. Even though it can be found near water, this species rarely swims and unlike its close relatives, rarely finds a home in sewers or in aquatic areas. Although it was formerly common in towns and farms of temperate regions, it has been largely driven out by the more aggressive Norway rat as well as killed off by increasing chemical pest control programs. Data have shown that R. rattus can reach elevations up to 250 m above sea level. (Corbet and Southern, 1977; Grzimek, 2003)

  • Range elevation
    0 to 250 m
    0.00 to 820.21 ft

Physical Description

Rattus rattus is a medium sized rat with relatively large ears and a tail that is nearly always longer than the body. Individuals weigh between 70 and 300 g, and are between 16 and 22 cm in head and body length and a tail length of 19 cm or longer. Males are longer and heavier than are females.

Many members of the species are black in color with a lighter colored ventral belly. The species is often divided into subspecies based upon color patterns which can occur in any combination of black, white, grey, and agouti.

The skull and nasal bones are relatively narrow. One of the main ways to differentiate between R. rattus and R. norvegicus is that R. rattus has a finer covering of hair, a lighter skull, and a slightly differently shaped upper first molar. (Allen, 1938; Corbet and Southern, 1977; Grzimek, 2003)

  • Sexual Dimorphism
  • male larger
  • Range mass
    70 to 300 g
    2.47 to 10.57 oz
  • Average mass
    200 g
    7.05 oz
  • Range length
    16 to 22 cm
    6.30 to 8.66 in
  • Average basal metabolic rate
    0.77 W
    AnAge

Reproduction

Social groups of R. rattus are often formed of multiple males and multiple females. One male is dominant and a linear male hierarchy may form. Two to three females are often dominant to all other group members except the dominant male. Females are generally more aggressive than males. The species is polygynous, and generally, the dominant male is the most successful breeder. Territories and mates are defended through aggressive behavior. If environmental conditions allow it, successful breeding may occur all year. (Corbet and Southern, 1977)

Rattus rattus is able to breed throughout the year if conditions allow. The peak breeding seasons are summer and autumn. Females can produce up to 5 litters in one year. The gestation period ranges between 21 and 29 days, and young rats are able to reproduce within 3 to 5 months of their birth. Neonates are altricial, like most rodents, and their eyes do not open until 15 days of age. Young remain hairless for much of their nursing period. Weaning and independence from the mother occur at about 3 to 4 weeks of age. (Corbet and Southern, 1977; Grzimek, 2003; Corbet and Southern, 1977; Grzimek, 2003)

  • Breeding interval
    R. rattus breeds year-round producing up to five litters in that time.
  • Breeding season
    R. rattus mates throughout the year if environmental conditions permit, however peak times are summer and autumn seasons.
  • Range number of offspring
    6 to 12
  • Average number of offspring
    8
  • Average number of offspring
    7.3
    AnAge
  • Range gestation period
    21 to 29 days
  • Range weaning age
    3 to 4 weeks
  • Range time to independence
    3 to 4 weeks
  • Range age at sexual or reproductive maturity (female)
    3 to 5 months
  • Range age at sexual or reproductive maturity (male)
    3 to 5 months

Because male members of R. rattus copulate with one female and then move on to the next, they don't contribute much to the care of the young. The young remain relatively helpless for about 2 weeks, until they begin to grow a pelage, their eyes open, and they are able to move around more. Weaning is accompanied by increased independence from the mother. Until these rats reach their full adult size, they stay in the nest built by their mother. Young rats are capable of reproducing by about 3 to 5 months of age. (Grzimek, 2003)

  • Parental Investment
  • no parental involvement
  • altricial
  • female parental care
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan/Longevity

Rattus rattus tends to live for about a year in the wild with an annual mortality rate of 91 to 97%. In captivity, it has been reported to live for up to 4 years. (Nowak, 1999)

  • Range lifespan
    Status: wild
    1 (high) years
  • Range lifespan
    Status: captivity
    4 (high) years
  • Typical lifespan
    Status: wild
    1 (high) years
  • Typical lifespan
    Status: captivity
    1 (low) years

Behavior

Rattus rattus tends to live in polygynous groups with multiple males and females. Dominant males have increased mating access and mate more frequently than do subordinate males. Females are usually more aggressive than males, but have been reported to be less mobile.

Black rats exhibit many destructive behaviors. These animals strip bark off of trees, contaminate human food sources, and are overall pests.

Rattus rattus is primarily nocturnal. It builds nests for young out of sticks and leaves, and sometimes locates nests in burrows. Depending upon habitat, individuals may be arboreal or terricolous. Often these rats use their climbing abilities to make a home in upper floors of buildings. This species has a highly adapted tail that is longer than its body. Being an avid climber that often lives on ships and in arboreal habitats, R. rattus uses this long tail to assist in balance. (Allen, 1938; Corbet and Southern, 1977; Grzimek, 2003; Nowak, 1999; Pye, Swain, and Seppelt, 1999)

  • Range territory size
    100 (high) m^2

Home Range

The home range of R. rattus is never more than about 100 square meters. It often has smaller territories. Territories surround food sources and are defended. (Nowak, 1999)

Communication and Perception

Rattus rattus is a somewhat vocal animal, producing squeaks when threatened or socializing. It also produces oil smears that are left along particular areas to illustrate territorial boundries. Hierarchy in groups is determined using aggressive threat postures and physcial contact. Vision, hearing, touch, and smell are all used in sensing the environment. (Nowak, 1999)

Food Habits

Rattus rattus generally feeds on fruit, grain, cereals, and other vegetation. It is an omnivore, however, and will feed on insects or other invertebrates if necessary. It consumes about 15 g/day of food and 15 mL/day of water. Because it consumes and destroys the food source during feeding, it can cause devastating damage to farms and livestock. Not only does it gnaw through many materials but it ruins more than that by excreting on the remains of its foraging efforts. (Nowak, 1999)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit

Predation

Known predators of R. rattus vary depending on environment. In urban or suburban areas, house cats are the main threat to its survival. In less populated areas, birds and other carnivorous animals prey upon it. One possible anti-predator adaptation is the array of color patterns found in this species. Some evidence suggests that color is related to geographical location and therefore ability to remain less conspicuous in the local environment. Also, rats are often aggressive toward other rats. Captive studies have shown R. norvegicus will kill R. rattus. Rattus rattus has a typical threat pose in which it stands on its hind feet and bares its teeth. (Nowak, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Impact of these animals on their ecosystems has not been studied. However, we may infer from their feeding habits that they have some impact on plant communities. As a prey species, they may impact populations of those animals which feed upon them. Also, they compete with other species of rodents, such as Rattus norvegicus. Rattus rattus is a disease vector, responsible for bubonic plague outbreaks and other diseases. This cosmopolitan species hosts a wide variety of internal and external parasites, up to 18 species of gastrointestinal helminths in some areas. (Desquesnes, et al., 2002; Mafiana, et al., 1997)

Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known benefits of R. rattus for humans. Norway rats, the closest related species, is often used for research and as pets. (Corbet and Southern, 1977)

Economic Importance for Humans: Negative

Rattus rattus is a pest and is dangerous to humans in several ways. First, these animals are severely destructive to crops, farms, and fruit trees. Not only do they feed on these but they tend to destroy what they are unable to consume. By urinating and defecating on remains of their meals, they ruin grain, cereals, and other food sources. This species is famous for its role in spreading the bubonic plague (Yersinia pestis) that took millions of lives in the middle ages. The fleas that live on these rats carry a number of diseases that can seriously harm humans, livestock, and other animals. (Allen, 1938; Corbet and Southern, 1977; Grzimek, 2003; Nowak, 1999; Pye, Swain, and Seppelt, 1999)

Conservation Status

Rattus rattus has no special conservation status. They are widespread and abundant, especially in areas where humans live.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Heather Gillespie (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Antarctica

lives on Antarctica, the southernmost continent which sits astride the southern pole.

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

Allen, G. 1938. The Mammals of China and Mongolia. Natural history of Central Asia. New York: American Museum of Natural History.

Corbet, G., H. Southern. 1977. The Handbook of British Mammals. Oxford: Octavo.

Desquesnes, M., S. Ravel, G. Cuny. 2002. PCR identification of Trypanosoma lewisi, a common parasite of laboratory rats. Kinetoplastid Biology and Disease, 1: 2. Accessed September 03, 2006 at http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=119323.

Grzimek, B. 2003. Grzimek's Animal Life Encyclopedia: Mammals. Pp. 126-128 in N Schlager, D Olendorf, M McDade, eds. Order: Rodentia, Vol. 16, 2nd Edition. Farmington Hills, MI: Gale Group.

Mafiana, C., M. Osho, S. Sam-Wobo. 1997. Gastrointestinal helminth parasites of the black rat (Rattus rattus) in Abeokuta, southwest Nigeria.. Journal of Helminthology, 71: 217-220.

Nowak, R. 1999. Walker's Mammals of the World (6th Edition). Baltimore, Maryland: Johns Hopkins University Press.

Pye, Swain, and Seppelt, 1999. Distribution and habitat use of the feral black rat (Rattus rattus) on subantarctic Macquarie Island. Journal of Zoology, 247: 429-438.

Veitch, D. 2006. "Rattus rattus" (On-line). Global Invasive Species Database. Accessed February 21, 2008 at http://www.issg.org/database/species/ecology.asp?si=19.

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