Rattus rattus
house rat
(Also: ship rat; black rat; roof rat)

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; Pye, Swain,, and Seppelt, 1999)

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)

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)

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)

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)

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)

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)

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)

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)

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, Ravel, and Cuny, 2002; Mafiana, Osho, and Sam-Wobo, 1997)

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)

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)

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