Interspecific interference behaviours by workers of the harvesting ant Messor capitatus (Hymenoptera Formicidae)

The different techniques employed by Messor capitatus workers to interfere with the activity of neighbouring heterospecific colonies are described for the first time. Observations and experiments conducted both in the field and in the laboratory allowed us to identify a behavioural task group of workers (defined as ‘sappers’) that have a direct detrimental effect on colony activity of heterospecific congeneric competitors. A rich repertory of interspecific interference behaviours are described. Sappers often gather around the entrance holes of other nests to limit or prevent (by threat displays, physical fighting, and nest-plugging with earth, pebbles or other materials) residents from emerging. All these strategies strongly affect the activity of the target colony that may be completely blocked as long as the sappers patrol the nest. Disturbance along foraging tracks as well as cleptobiosis (food robbing) at nest entrances have been recorded. M. capitatus workers are also very effective at monopolizing conspicuous food sources, chasing off workers of other species (even if they had first discovered the food), and inducing them to barricade themselves inside their nest until the newly-discovered food source has been completely depleted. The possible effects of M. capitatus interference strategies on the ecology of neighbouring colonies are discussed.