Ant invasions are a nuisance for picnickers, but for California's coastal horned lizards, the proliferation of one foreign ant species threatens their very survival. The results of two new studies indicate that Argentine ants have displaced a number of the native ant species that the lizards feed on, and eating the intruders instead, it seems, is not an option. The findings appear in the current issues of the journals Conservation Biology and Ecological Applications.

The two-millimeter-long exotic ants are thought to have come to the U.S. via cargo ships from Argentina around the end of the 19th century. According to Ted J. Case of the University of California at San Diego, although the ants reached southern California about 100 years ago, they have only recently become problematic--largely because urbanization has made the area more attractive to them. Their arrival adds insult to injury for the lizards, whose habitat has already undergone fragmentation, because the Argentine intruders have made it quite clear that they won't share their habitat with the ants the lizards like to eat: the territorial creatures have killed and displaced ants 10 times their size.

Why don't the horned lizards just eat the tiny Argentine ants, whose biomass actually exceeds that of the larger native ants? Apparently, the charismatic reptiles need a variety of ants in their diet, especially when they're young. "Our work demonstrates that invasions can have community-wide effects," says Andrew Suarez, now at the University of California at Berkeley."Essentially, the impact of Argentine ants in California starts with the displacement of native ants and then cascades throughout the ecosystem." For the coastal horned lizard to survive in this region, he notes, "we not only have to make sure that enough habitat is put aside, we also have to make sure that the remaining habitat is monitored to prevent the invasions of exotic ants."