Anoplophora glabripennis (Motschulsky) (Asian longhorned beetle) was found attacking street trees in New York City and Chicago in the 1990s, after its accidental introduction from East Asia, and is currently the subject of a major eradication campaign by the U.S. Department of Agriculture. The borer has been a destructive outbreak pest in poplar plantations in China for over 20 yr, but it has been collected only rarely in nearby South Korea. To learn more about the species in natural forest stands, we surveyed nine montane locations across South Korea in 2000 and 2001. The primary hosts of Korean A. glabripennis are Acer mono and A. truncatum, which grow in riparian habitats and rocky ravines. We surveyed two locations in Mt. Sorak National Park intensively, mapping all host trees. Less than 10% of the trees at each site exhibited evidence of beetle damage, and few adult beetles were observed. We hypothesize that the varying dynamics of A. glabripennis populations across its geographical range may be explained by considering it as an “edge specialist,” which evolved in riparian habitats.