The organization of artificial heterospecific ant colonies. The case of the Manica rubida/Formica selysi association: mixed colony or parallel colonies?

We studied the spatial and social organization of homospecific and heterospecific colonies of two ant species Manica rubida (Myrmicanae) and Formica selysi (Formicinae) reared without a queen in artificial nests. We used a method based on individual labelling and automated photographic recording of data. The two species, which are forced to live together in the same artificial mixed colony, show the same spatial organization as they do in control homospecific colonies. The Manica rubida were mostly clustered in one chamber while Formica selysi workers were spread throughout the nest. Formica selysi individual spatial profiles are very heterogeneous while in the other species they are very homogeneous. By using taxonomical techniques on behavioural data we show that the two species within the mixed colony are clearly distinguishable. An artificial association of these two species may therefore be considered to be a juxtaposition of two colonies functioning in parallel, rather than a "mixed colony".