Research

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.

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.

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.

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.

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. 

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.

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.

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.  

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.   

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.

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.