Formicoxenus provancheri forms separate, small nests at the edge, or in the wall of, the larger Myrmica incompleta nests. The colonies do not mix as the galleries of the Formicoxenus provancheri nest are too small to allow the larger hostants to enter. Myrmica incompleta seem to show little aggression towards the parasitic Formicoxenus provancheri, and the two species mutually accept each other. However, the broods of the two species are always kept in separate chambers as Myrmica incompleta will prey on Formicoxenus provancheri larvae (2) (4).
Each colony of Formicoxenus provancheri contains only one fertile female. Unlike other ant species, only a few Formicoxenus provancheri remain in the nest and tend to the brood that the queen produces. The largest numbers of Formicoxenus provancheri are found in the Myrmica incompleta nest. These individuals are strongly attracted to both Myrmica incompleta adults and larvae, and will frequently mount and lick the host ants in order to receive regurgitated food. This behaviour, known as ‘shampooing’, may also be used to obtain the Myrmica colony odour. Formicoxenus provancheri do not forage, and are instead completely dependent on the larger host ants for food (2).
Formicoxenus provancheri has also been shown to possess the ability to follow scent trails deposited by Myrmica incompleta workers. This trail allows Formicoxenus provancheri to follow hosts to new nest sites (5).