"Karl Marx was right, socialism works, it is just that he had the wrong species,” the renowned Harvard conservation biologist Edward O. Wilson once joked. 

Clever, yes. Accurate? Partly. Ants are well known for their division of labor, and they raise young cooperatively. Not all ants in a colony are fertile, so it truly does take a village to raise a baby ant. 

But ant societies also are extremely hierarchical, with queens, workers, and soldiers; and David Holway, a professor in the Ecology, Behavior and Evolution Section of UC San Diego’s Division of Biological Sciences, is studying a species of ant that is, by any measure, frighteningly competitive. 

Researchers believe that Argentine ants arrived in New Orleans on a ship from Buenos Aires or Rosario around 1890. Like many so-called “invasive” species, the Argentine ants outcompeted many native species. By 1920, they had spread through the American South, becoming notorious for the damage they wreaked on sugar cane.  

Today, Argentine ants are considered “a global mega-colony” with enormous, genetically linked populations in America, Europe and Japan. Researchers report that “the extent of this population is paralleled only by human society.” In fact, as Holway points out, one reason Argentine ants are so successful is that they thrive in places inhabited by humans, another species that successfully spread over the planet. 

There are many reasons to care about ants, and practical reasons to pay attention to Argentine ants, according to Holway, who also is faculty director of UC San Diego's Natural Reserve System, stretches of protected southern California land where cutting-edge research takes place. Argentine ants damage crops, and their ability to colonize new territory is a threat to native species in California and elsewhere. 

More than 100 years ago, H.G. Wells sketched a fantasy where ants rivaled humans for control of the Earth in his 1905 short story, “Empire of the Ants.”  While that scenario remains in the realm of imagination, 100 years from now California’s landscape might look very different, thanks to the adaptability and highly organized efforts of Argentine ants.

Q&A with David Holway:

How many ant species are out there, and why are they important?

Answer:

There are probably about 20,000 species of ants in the world, more or less 12,000 of which have been named, and roughly 250 species that have been described in California. But diversity isn’t necessarily correlated with how important they are ecologically.

People who study ants, including E.O. Wilson, will tell you that it’s not their diversity but their abundance. Particularly in the tropics, their biomass is high.

What role do they play in ecosystems?

Answer:

They’re important scavengers and predators and they participate in mutualisms with other species. We’re studying one of these mutualisms in our lab that involves the coast barrel cactus. Many species of barrels produce nectar outside of their flowers.  The nectar comes from small glands called nectaries. These attract native ants and, in return, ants protect the cactus from insect herbivores. The cactus is already protected from vertebrate herbivores by its spines. So with the ants, they’re covered when it comes to both types of herbivores.

Why have Argentine ants in particular been so successful?

Answer:

On the face of it, you wouldn’t think they’d be so invasive. Argentine ants have a narrow environmental tolerance; they like areas that are warm and humid, and the queens don’t have mating flights, so the colonies disperse slowly. 

But humans have inadvertently carried the Argentine ant all over the place. And the ants are very opportunistic in terms of where they nest. Most people think of ants’ nests as catacombs in the soil. But Argentine ants move their nests around a lot, and they’re flexible about where they live. They like rotting wood, the top layers of soil, wild plants, potted plants, wood chips, compost, trash. It’s that nesting behavior that allows them to get around so much, and to live close to us. They thrive in California’s Mediterranean climate.

How serious is the threat Argentine ants pose to California's native ant species?

Answer:

There’s no evidence that the Argentine ant has caused the extinction of other ant species in California. Not yet, at any rate. There may have been extinctions elsewhere that nobody knows about. But many native ant species in California now inhabit a fraction of their former range. In the case of harvester ants, they have been displaced by Argentine ants at the landscape level in portions of California.

The Argentine ant has been implicated in the decline of the coast horned lizard.

Answer:

Yes. Like other reptiles and amphibians in California, the coast horned lizard is completely absent from large portions of its former range. You can still find them in the chaparral of the hills outside San Diego. But it’s interesting to talk to people who grew up in San Diego. They used to find them in their backyard and the lizard went up as far north as the Sacramento Valley. 

How has the Argentine ant contributed to the lizard's decline?

Answer:

It’s clear that the Argentine ants are displacing the native harvester ants that the horned lizards feed on. The lizards seem to really like harvester ants. If a horned lizard finds a harvester ant colony they’re set. They can repeatedly come back to get food.  If they feed on a spider or a beetle it’s a one-off. Argentine ants are much smaller and really don’t provide the same food supply.

Many people would like to know about the impact of this invasion on agriculture.

Answer:

Citrus and grapes are affected. The ants actually protect aphids and mealybugs, which feed on these crops. This is another example of the mutualism that ants are noted for.

How does mutualism work?

Answer:

Aphids have tubular beak mouth parts that allow them feed on plant sap, and the particular shape also commits them to a certain plant. They’re soft-bodied and don’t move around so they’re susceptible to predators like ladybugs, and they’re also parasitized by wasps.

Argentine ants protect the aphids and mealy bugs from their enemies. They just chase the predators away. It’s amazing to watch. If you sit around long enough you can see them chase off ladybugs.  

Overall, how urgent is the problem of Argentine ants?

Answer:

It’s hard to tell. The reason the horned lizard has gotten attention is that it’s a familiar and really cool-looking vertebrate. But we do see these changes on the landscape level, and recently we discovered that the Argentine ant has been introduced to the Channel Islands.

We’re working with the U.S. Park Service, the U.S. Navy, and The Nature Conservancy to control them. The fear is that if the Argentine ants spread they will drive the ants that are endemic to the Channel Islands — that live there and nowhere else — into extinction.   

How do you know if the ant in your kitchen is an Argentine ant?

Answer:

You don’t. But in coastal California, in most urban and suburban areas, they’re very common, and also in the Central Valley agricultural areas. Chances are if you go into an urban environment and you pick up an ant, it’ll be an Argentine ant.

Many people have seen parallels between ant society and human society, including E.O. Wilson. What is it about ants that causes us to compare ourselves to them?

Answer:

Ants do have behaviors that are really, really remarkable. They have wars, they have caste societies and, for better or worse, they often live in close proximity to us.

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