They are quiet, live mostly underground, and they don't sting humans. But even insect lovers dread the arrival of Argentine ants (Linepithema humile). The voracious appetite of this alien species and its tendency to displace native ants has been well documented, but until recently scientists knew very little about the specific mechanisms used by the insect to gain control of a particular area. Now a new study, published in the January issue of Ecology, reveals some interesting findings about these aggressive ants.

The study, conducted by David Holway at the University of Utah (now at UC San Diego), examined the Argentine ant and seven species of native ants it displaces in the riparian woodlands of Northern California. Baits made of tuna and apple jelly were placed in areas where native ants and Argentine ants foraged in close proximity to one another. By studying their reactions to the bait and their interactions at the bait stations, Holway was able to determine several key things that make the ant such a successful invader.

Argentine ants located bait as quickly or more quickly than the native species. And along the invasion lines, Argentine ants controlled a greater proportion of bait than did their competitors. But in one-on-one interactions between individual Argentine ant workers and workers from the other species, the Argentine species experienced only mixed success.

Argentine ants employed both chemical defensive compounds and physical aggression during confrontations with other ants. Although chemical defense was typically more effective than physical aggression, the chemical compounds of the invasive ants did not appear more repellent than those found in the native species. In addition, Argentine ant workers were not able to overcome native ants on a consistent basis.

But the invasive species -- colonies were more successful on the whole than the native ant colonies. The discrepancy between worker-level and colony-level su
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Contact: Alison Gillespie
Alison@esa.org
202-416-6181
Ecological Society of America
12-Jan-1999