Intraspecific aggression in the brown rover ant, Brachymyrmex obscurior

Invasive ant species often show unicoloniality, forming networks of connected colonies (i.e. supercolonies), which may extend hundreds or even thousands of kilometers. These "supercolonies" lack intraspecific aggression, thus fighting between colonies is absent. Unicoloniality may be an adaptive mechanism that allows for invasive ant species to reach higher population density and achieve ecological dominance. We used aggression assays to study unicoloniality within and between colonies of the invasive brown rover ant, Brachymyrmex obscurior on the Florida Atlantic University campus in Jupiter, FL. We found that the four B. obscurior colonies could be behaviorally divided into two areas: workers from both colonies in either region never showed intraspecific aggression while workers from colonies in opposing areas always showed intraspecific aggression, often fighting to the death. Thus, B. obscurior appears to show very localized unicoloniality, with neighboring colonies forming small supercolonies.