Interspecific hierarchies from aggressiveness and body size among the invasive alien hornet, Vespa velutina nigrithorax, and five native hornets in South Korea.

The range of the invasive alien hornet, Vespa velutina nigrithorax, has been expanding since its introduction to Korea in 2003. Here, we compare the aggressive behaviors and body size of V. velutina nigrithorax with five native hornet species to identify the interspecific hierarchies that influence the rate of spread of this species. Aggressive behaviors were classified into 11 categories, and each interaction was scored as a win, loss, or tie. We found that V. velutina was superior to V. simillima in fights that V. velutina won and showed a high incidence of threatening behavior. V. mandarinia outperformed V. velutina in fights that V. mandarinia won and grappling behavior was common. V. analis was superior to V. velutina in fights that V. analis won and showed a high degree of threatening behavior. V. crabro was superior to V. velutina in fights that V. crabro won and showed a high rate of threatening behavior. V. dybowskii was superior to V. velutina in fights that V. dybowskii won and showed a high incidence of threatening and grappling behaviors. The body size of V. velutina was greater than V. simillima (although not statistically significant) and smaller than all other Vespa species. Therefore, according to this study, the low interspecific hierarchies of V. velutina seem to be a major cause of the slower spread in Korea than in Europe. However, over time, its density has gradually increased within the forest, where it seems to be overcoming its disadvantages and expanding its range, possibly because the large colonies and good flying abilities of this species help it secure food.