Against the odds of the ant competition hierarchy: submissive Myrmica rugulosa block access of the dominant Lasius fuliginosus to its aphids

Many ant assemblages are organised in competitive hierarchies. Myrmica rugulosa, a submissive species at the bottom of the ant competition hierarchy, temporarily took over groups of the myrmecophilic aphid Stomaphis quercus, which is strictly associated with the territorial ant species Lasius fuliginosus. Such previously unknown intervention happened repeatedly on the nest tree of L. fuliginosus. Masses of M. rugulosa intruded into bark crevices harbouring the aphids, and blocked with their own bodies access of L. fuliginosus to the aphids. Lasius fuliginosus showed no aggression towards the intruders, but walked around and on M. rugulosa clusters, palpating foreign ants with their antennae. Their only countermeasure was to briefly drag or carry individual M. rugulosa workers that pressed themselves down and froze for the moment, and then resumed their activities. We interpret the behaviour of M. rugulosa, in the context of its already known interspecific relations, as a specific competitive means of existence with higher-ranked species. The behaviour—by strict definition neither interference nor exploitation competition— effectively combines submissiveness, appeasement and tenacity. We discuss similarities between such behaviour and related behaviour reported earlier in a few other Myrmica species and Manica rubida while confronting physically stronger ants.