Brood-holding causes workers to pay attention to the queen in the carpenter ant Camponotus japonicus

[Abstract]Brood accumulation, a fundamental behavior of offspring care in the carpenter ant Camponotus japonicus, is driven by alternation of holding run and empty-handed run behaviors. In the holding run, a worker holds a brood with her mandibles and carries it to the queen (holding run). After releasing it beside the queen, she hurries back to another brood (empty-handed run). To address the motivation for the brood-accumulation task, in this study, I observed these behaviors under experimental conditions. When workers performed the task in a situation that involved selection between their own and unfamiliar queens, they ran in significantly more restrictive ways during the holding run than during the empty-handed run. Hence, holding represents a different motivational state than empty-handed. In a second experiment, the workers were suddenly presented with an unfamiliar floor during the task. Regardless of whether they were holding or empty-handed, their running traces on the familiar floor were simple, whereas on the unfamiliar floor they were more complex. These results show that holding workers would pay attention to the queen, exploiting cues on the floor to restrict their responses to the queen.