In the past few years, families living in different parts of Tokyo have noticed an increase in damage from rats. Problems reported to city ward offices and public health centers include rats chewing up clothes in closets, stealing food from kitchens and damaging gas pipes. The Health and Welfare Ministry estimated there were 6,325 cases of rat infestations in 1988. Ten years later, that number had bounded sharply to 34,097. These 15 to 20 centimeter rodents are smaller than Norway rats, the brown variety usually found slinking about in sewers or shrubberies.
Roof rats are identifiable by their long tails, which have a scale-like pattern.
Roof rats have long been a menace in commercial areas of the city, but in the 1970s more of the pests began chewing up office wiring and even gas hoses in restaurants, sometimes leading to gas leaks. Now roof rats are invading residential areas. Their proliferation has been possible because of their strong resistance to rat poison. Unlike the regular Norway rats, which have little resistance to rat poison, roof rats are much tougher. In laboratory tests, roof rats have survived on a diet of only rat poison for more than a month.