L. humile shows aggression not just to neighboring colonies of Argentine ants, but to any ant species. The Argentine rapidly overruns native ants in the habitats it invades. Whereas undisturbed environments might typically house upward of 10 ant species, areas that include the Argentine variety accommodate no other species.
Think of the Argentine ant as a city street tough that moves to small-town U.S., Holway said. The kid needed that big city swagger to survive on mean streets but doesn't just lose it if he moves to a mild-mannered town. The aggression and street smarts learned in an urban environment enable the transplant to establish a massive crime ring and take over the town.
What the future holds
Although Argentine ants are susceptible to some of the insecticides used in California's citrus groves, the chemicals have not made much of an impact on them. Their numbers are too large, and their supercolony spans too broad of an area. Eliminating the ants in a single household or field is temporary, and only means that it will be invaded again in the near future.
Nor is the large-scale use of pesticides the best option from an ecological standpoint. The toxic chemicals get into drinking water, not to mention rivers and oceans. Holway's lab now is looking to identify the ant's native parasites and diseases that help control L. humile in native habitats. Introducing these germs to the ants' new homes may start to keep their numbers in check.
Tsutsui himself hopes to use the new genetic data to identify how the Argentines use chemicals to lay down trails for fellow ants to follow. He also hopes to identify how L. humile learns to recognize nest mates. If Tsutsui can learn the chemical signature that identifies a colony, he can attempt to disrupt this process.
"We would be happy if, on a large scale, we can reduce the impact of these native ants so that they're only a minor pest," says Les Greenberg, an entomologist at the University of California, Riverside, who was not involved in the study. "It's probably impossible to eradicate them once they've been established."