Turning Ant Against Ant: Controlling a Super-Colony

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In the early 1890s, tiny brown ants from Argentina were discovered in the Port of New Orleans crawling out of bags of sugar. No one was alarmed at the time but in retrospect, they should have been.

NPR's John Nielsen reports.

(Soundbite from Them)

Unidentified Man: Get the antenna. Get the antenna.

(Soundbite of gunshots)

NIELSEN: But entomologist Brian Fisher of the California Academy of Sciences says even the tiniest ants can be ferocious. For example, here's what happens when a large ant native to California meets up with a group of extremely small Argentine invaders.

Mr. BRIAN FISHER (California Academy of Sciences): The Argentine ant runs up, maybe six of them, grabs each of the legs of this ant, pulls it to the ground and pulls it apart.

NIELSEN: Fisher says this kind of aggression is partly why tiny Argentine ants have been able to take over so many habitats.

But there's another reason, too. In the United States, these ants hardly ever fight with each other. Neil Tsutsui, an entomologist with the University of California at Irvine, says the Argentine colonies help each other find shade, food and water.

Mr. NEIL TSUTSUI (University of California at Irvine): And because of this cooperation their population densities can really get very large. So, for example, here in California almost the whole introduced range in this state is dominated by a single behavioral unit that's cooperative from San Diego all the way up to San Francisco.

NIELSEN: If you live in California, Tsutsui says you've probably seen these ants in your house.

Mr. TSUTSUI: They come in, often in very large numbers, looking for food or looking for water or, you know, discovering the pet food bowl.

NIELSEN: They also do a lot of damage in farmer's fields by killing off the native ants that devour crop eating bugs.

Now for years it was assumed that Argentine ants had always formed friendly super-colonies, but then about five years ago Tsutsui went to Argentina and saw colonies of these ants fighting brutal civil wars. He suspected that these wars occurred because the ants in Argentina are much more genetically diverse than those found further north. Because of that, each colony had its own chemical signature and colonies with different smells just didn't seem to get along.

In his lab at UC Irvine, Tsutsui began experimenting with various chemical compounds, looking for one that might start a civil war. The first combinations he tried didn't do anything, but then one day he painted a new formula onto the back of an Argentine ant and dropped it into a treated petri dish full of relatives. It was quickly torn to pieces.

Tsutsui says it's too early to say whether compounds like these will someday end up inside cans of ant spray sold at local hardware stores.

NIELSEN: Civil war is never pretty, he says. But in this case it could be a good thing.

John Nielsen, NPR News, Washington.

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