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 continuously expanding since its invasion of Korea in 2003. Here, we compared the aggressive behaviors and body size of V. velutina nigrithorax with five native hornet species to identify the interspecific hierarchies that contributes to the spread of this species. Aggressive behaviors were classified into 11 categories and each interaction was scored as a win, loss, or tie. As a result, V. velutina was superior to V. simillima in 153 fights where V. velutina won 71% and showed a high incidence of threatening behavior. V. mandarinia outperformed V. velutina in 104 fights where V. mandarinia won 91% and grappling behavior was common. V. analis was superior to V. velutina in 67 fights where V. analis won 76% and showed a high amount of threatening behavior. V. crabro was superior to V. velutina in 93 fights where V. crabro won 73% and showed a high rate of threatening behavior. V. dybowskii was superior to V. velutina in 132 fights where V. dybowskii won 91%, and showed a high rate of threatening and grappling behaviors. The body size of V. velutina was larger than V. simillima (although not statistically significant) and smaller than all other Vespa species. Therefore, according to the results of this study, the low interspecific hierarchies of V. velutina seems to be a major cause of slower spreading rates than it has shown in Europe. However, over time, its density has gradually increased within the forest, in which it seems to be overcoming its disadvantages and expanding its range, possibly as large colonies and good flying abilities make it easier to secure food.