In eusocial aphids, sterile soldiers cannot discriminate kin from non-kin, and the colony members (their clones) can potentially disperse between colonies. Thus, clone mixing can easily occur and may lead to disrupting eusociality because kin selection based on kin recognition does not operate. Here, we report that 1. clone mixing occurs in the eusocial aphid Ceratovacuna japonica, 2. soldiers cause significant delay in the predation by the specialist predators, 3. the alarm pheromone which is secreted by the aphids that were attacked by predators induces aphids' dispersal, and thereby facilitates clone mixing.Therefore, these results suggest the existence of factor that can remove selfish clones, producing only non-soldier individuals, from aphids’ population. We conclude that this factor may be the predation, because the intensive predation pressure that is often observed in this species can lower the fitness in the mixed clones, selfish clone and altruistic clone, colonies with less soldiers.