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Rats (035) Print Fact Sheet

Common Name

Polynesian rot, black rat (also called ship rat), brown rat

Scientific Name

Rattus exulans (Pacific rat); Rattus rattus (black rat); Rattus norvegicus (brown rat).


Rattus exulans - widespread through Asia and the Pacific islands; Rattus rattus - worldwide; Rattus norvegicus - worldwide with human settlement.


Main crops that are attacked are cassava, cocoa, coconut, oil palm, peanut, maize, rice, sweetpotato, and others in storage.

Symptoms & Life Cycle

Habitats: All three species can be found in grasslands, scrub, forests and urban areas. The Polynesian rat does not burrow, but digs small holes and nests mainly on the ground. The brown rat makes burrows and nests underground. The Polynesian and black rat climb, the brown rat rarely does. Black rats often nest in trees. The brown rat swims well, and favours wet habitats. In Pacific islands countries, it is probably more common in ports and towns than village gardens.

Life Cycles: If food is available, rats breed. Females can reproduce several times a year. Sexual maturity is 2-3 months, gestation (period between fertilization and birth) is 21-24 days and average litter size is 6-10. Life expectancy is 12-15 months.


All three damage crops, and are a threat to biodiversity. Apart from fruits, grains and other plant material, these rats eat insects, reptiles and young birds. They are pests of agriculture crops, including rice, maize, sugarcane, coconut, cocoa (Photo 1), pineapple, peanuts and root crops. They eat stored foods, and spoil them by urinating and defaecating on them. Rats carry a scrub typhus in Santa Cruz, Solomon Islands, which is transmitted via the fleas they carry.

Note, damage in coconuts is not directly related to the number of nuts damaged; it occurs early and palms compensate for about 50% of the loss. In cocoa, this is not the case as damage occurs when pods are near maturity.

Detection & Inspection

Characteristics of the three species are listed as follows:

Polynesian rat (Photo 2):

Black rat (Photo 3):

Brown rat (Photo 4):

A comparison between the black and brown rat is provided (Diagram).





Plant-derived pesticides:

Commercial pesticides:

Note warfarin is banned in Europe and, in the USA, so-called second generation anti-coagulants, e.g., brodifacoum, can only be used by professional pest control operators. Warfarin and brodifacoum are registered in all states and territories in Australia, but brodifacoum can only be used in and around building, not in open areas.

AUTHORS Helen Tsatsia & Grahame Jackson
Photos 2&4 Gerald McCormack, Cook Islands Biodiversity & Natural Heritage ( Photo 3 Wikipedia. ( Diagram Wikipedia Black rat. ( Photo 5 Snap trap. (

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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