Ritualised versus aggressive behaviours displayed by Polyrhachis laboriosa (F. Smith) during intraspecific competition.

The intraspecific territoriality of Polyrhachis laboriosa was studied thanks to dyadic confrontations between nestmates and alien foragers in chemically marked and unmarked arenas, complementing experiments and observations in nature. When foragers meet, the alien flees while the resident attacks, especially when on a marked area. However, when an alien scout extends its territory, it attacks the resident ant, such confrontation resulting in a high rate of reciprocal full attacks. When surrounded by several residents, the intruder is always spread-eagled if it does not succeed in fleeing. We described ritualised displays, such as threatening (opening mandibles; bending the gaster) or appeasing behaviours (antennal boxing; attempt at trophallaxis; pupal posture; raising the gaster). They occur only when the encounter maintains a low level of aggression, during laboratory experiments, or in nature during encounters involving a queen or an experimentally-introduced intruder. Foraging queens are tolerated on the territories of conspecific mature colonies. When they encounter resident workers, reciprocal avoidance occurs. Nevertheless, the latter perform ritualised displays when the queens approach their nest or attempt to rob their prey. This situation seems to compensate in part the archaic semi-claustral mode of foundation of this species, as the queens are indirectly protected by their conspecifics who do not tolerate other competitors around large food sources.