Rats - Species
The most widespread species of rats are Rattus norvegicus, the Norway or brown rat; Rattus rattus, the black, ship, roof, or alexandrian rat; R. exulans, the Polynesian rat; and Bandicota bengalensis, the lesser bandicoot rat. Both R. norvegicus and R. rattus are found around the world, and these are the two commensal species found in North American cities. They are longtime residents, firmly established on this continent by 1775. The Norway rat is found in temperate areas worldwide, although it originated in Japan and Eastern Asia, where it lived in burrows along river banks and later in rice fields.
Rattus rattus, like R. norvegicus, originated in Asia. It is thought to have been brought to Europe during the Crusades, although some records indicate it was present in Ireland as early as the ninth century. Rattus rattus arrived in North America with the early settlers, and its presence is recorded as of 1650. Early explorers brought R. rattus with them to South America as early as 1540. The two species spread worldwide, traveling in sailing ships to new ports.
Less global but no less commensal is the Polynesian rat, found from Bangladesh to Vietnam, throughout the East Indies, and in Hawaii and on other Pacific islands. The lesser bandicoot rat has been found in its natural habitat of evergreen jungle and oak scrub in Sumatra, Java, Sri Lanka, Pakistan, Burma, and Penang Island off the Malay peninsula, but in this century it has also become common in urban areas in India (it reproduces more quickly than any other rodent; a female lesser bandicoot rat can have a litter of seven every month).