The largest indoor cockroach species in Japan, the American cockroach, has invaded northern Kyushu and is breeding in large numbers locally. Reports from Fukuoka City residents have surged, with these giant cockroaches even swarming out of street drain covers, causing considerable alarm. Experts point to global warming as the cause.
According to the Nishinippon Shimbun, a 61-year-old male resident of Sawara Ward, Fukuoka City, expressed his horror, saying that this summer saw an unprecedented appearance of giant cockroaches in his home—they were enormous and numerous. Since July, he has spotted about 30 of them; only two or three were the small, black cockroaches normally seen, with the other 90% looking quite different. He described them as somewhat brown with white ring-like markings. Only after an online search did he discover they were American cockroaches. It is understood that Japan's native Yamato and Oriental cockroaches are typically 2 to 3 centimeters in length.
Maruyama Munetoshi, a 51-year-old associate professor at the Kyushu University Museum, stated there is no doubt that their numbers in northern Kyushu have surged dramatically over the past two or three years. On summer nights, most cockroaches spotted outdoors are American ones.
Body length 30-40mm, originally from Africa
This cockroach species measures about 30 to 40 millimeters in length and is native to Africa. They are not cold tolerant; if temperatures stay below 5°C for about a month, they will die. In the past, arriving with cargo from Okinawa to northern Kyushu, they could only survive in boiler rooms of buildings or well-heated corners of busy districts. Now, however, their numbers rival the commonly seen small black cockroach—clearly, they have fully taken root, and the cause is global warming.
Meteorological data shows Fukuoka City's average lowest temperature in February climbed from 1.24°C in 1921–1925 to 4.92°C in 2021–2025. As temperatures rise, American cockroaches are not only expanding their habitats, but persistent heat waves are also extending their period of outdoor activity and reproduction.
Warm, Food-Rich Drains Become Cockroach Paradise
Particularly noteworthy are the drain covers leading to the sewers. The internal environment is cave-like, warmer and more humid than outdoors, with kitchen scraps and other food sources available and no natural predators, making these drains a true "paradise" for American cockroaches.
Between 2020 and 2024, the Fukuoka City government received a total of 215 complaints about cockroaches crawling out from drain covers, and during the same period, used rubber seals to block 160 drain covers. The sewage management section urges residents not to dispose of kitchen waste and used oil into drains, but rather to treat them as burnable garbage, believing this is an effective measure to control cockroaches.