The Argentine ant was first detected in the United States in 1891, and since then it has displaced most native ants from the areas that it has settled. Tsutsui et al. explain in the May 23 Proceedings of the National Academy of Sciences that the immigrants benefit from their genetic homogeneity, which makes them less inclined to fight each other and more inclined to form cooperative supercolonies (Proc. Natl. Acad. Sci. USA 2000, 97:5948-5953). Two immigrants are still ready to fight each other if they find that they are sufficiently genetically distinct, but this scenario is far more likely to occur in Argentina than in the USA. The immigrants' genetic diversity, as measured here by microsatellite sequencing, was sharply reduced by a bottleneck that presumably occurred at the time of migration from Argentina. Introducing new alleles into the immigrant populations may increase genetic diversity enough to increase intra-species agression and give the natives a chance.