Four species of Simuliidae, Simulium (Eusimulium) subcostatum chejuense n. ssp., S. (Wilhelmia) takahasii (Rubzov), S. (Odagmia) iwatense (Shiraki) and S. (Simulium) japonicum Matsumura were collected from Cheju Island in Korea. This is the first record of this group of insect from Cheju Island. Both adult and immature stages of the new subspecies are described in this paper.
