Social insects use both genetic and environmental recognition cues when making nestmate discriminatory decisions. We examined the role of environmental cues (derived from diet) on nestmate recognition in two populations of the Argentine ant, Linepithema humile. We discovered that the two populations differ in their response to environmentally-derived nestmate recognition cues. Ants belonging to the California supercolony are strongly affected by the imposition of prey-derived hydrocarbons and spatially-isolated colony fragments provided with different prey (B. germanica or S. longipalpa) display high intracolony aggression when reunited. In contrast, colonies of Argentine ants from the southeastern U.S. show little or no aggression when subjected to the same treatment. Our results indicate that field-collected colonies of L. humile already possess hydrocarbons in the range of those provided by S. longipalpa, with colonies from the southeastern U.S. having significantly higher initial levels of Supella-shared hydrocarbons. When raised on prey diets, Argentine ants from both regions acquired additional amounts of Supella- and Blattella-specific hydrocarbons. In both populations, the increase in the level of Supella-specific hydrocarbons was not significant, while the increase in the level of Blattella-specific was significant. In California, intracolony aggression was induced, most likely as a result of low initial levels of Supella-specific hydrocarbons. Blattella-fed ants from the southeastern U.S. probably recognized former nestmates raised on the S. longipalpa diet, since ants raised on both diets had high initial levels of Supella-specific hydrocarbons.