Why are rover ants (Brachymyrmex patagonicus) so difficult to control?

Rover ants are an exotic species that has established itself successfully in the southern United States. They have become of concern for pest control professionals who have found them especially difficult to control. We report some aspects of this species’ biology that are associated with difficulties controlling this pest. We reared rover ant colonies from over a hundred field collected queens in Tucson, AZ. The following observations were made over the next 12 months in which 38 of the initial colonies developed and became fully functional. We observed the formation of satellites nests away from the main colony. Ant colonies established enduring satellite nests within less than a week of obtaining access to a new environment. We also separated groups of workers from the main colony in order to determine the time it takes for a queen-less colony fractions to die off. Colony fractions were observed to survive for over 3 months after being separated from their parent colony. Finally, we tested the level of aggression between ants of different colonies. Rover ants showed high levels of aggression towards individuals of a different colony which would prevent them from having high colony densities typical of invasive species. Our results suggest that their tendency to establish long lived satellite colonies is an important factor for the difficulty in controlling rover ants. Invasion of structures by these ants is most likely the result of one highly prolific, polydomous colony instead of many small colonies.