Although the red imported fire ant, Solenopsis invicta Buren, has spread across the southern United States, its population varies widely from one area to another. Earlier research has demonstrated that queens that land in areas with a native ant population suffer high levels of predation, but it has been assumed that once the first workers are present, the colonies vulnerability rapidly decreases. Recent laboratory studies, reported elsewhere, demonstrated that several native ant colonies were able to raid and destroy small S. invicta colonies. One of these native species was Solenopsis (Diplorhoptrum) molesta. We report here that small colonies of S. invicta were unable to establish in plots with the thief ant, Solenopsis molesta (Say), but were able to establish in an identical plot with no S. molesta. These results suggest that high density of at least one species of native ant can eliminate or at least reduce the establishment of small colonies of S. invicta that may have started to develop after the escape of the founding queen.