Bombus terrestris is widely used as an agricultural pollinator in many countries, including Japan. In some of these countries, B. terrestris has become naturalized, and the risks of such invasions are a concern for the conservation of native ecosystems. In Japan, invasions of B. terrestris have occurred in Hokkaido, northern Japan, since 1996, and areas of naturalization are growing. Invasions of B. terrestris in Japan have predominantly occurred in human-modified areas, such as open agricultural areas, which are comparable to the preferred environments of the bumblebees' original distribution ranges. However, current affected areas also include natural habitats such as coastal and alpine grasslands. Important natural vegetation in Hokkaido is now suspected to suffer as a result of B. terrestris invasions, and therefore continuous monitoring is needed.