Disappearing Argentine Ants (Sally, Cupertino, CA, USA)


I have lived in my present house, in Cupertino, CA (a suburb of San Jose) for 20 years. For the first ten of that, ants were very invasive (into the house), and hard to control. A scientist at Stanford University, D.M. Gordon, published an article in the local paper, saying that the ants in the area were argentine ants. However, for the last couple of years, there are almost no ants at all---not only in my yard, but in the whole neighborhood. I have had a couple of instances of ants showing up in my "no ant" zone (about 3 feet around the walls of my house), but they were much smaller than the argentine ants, and when I invited them to leave, using black pepper by the entryways and on any apparent nests in that zone, they politely did. Leave. When I look around the yard, and the neighborhood, for ants, usually I don't see any. This seems like a bad thing to me, I thought ants were supposed to be very good for the soil. Any thoughts?

- Sally
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Dear Sally,

Thank you for contacting AntBlog with your observations about Argentine ants in your neighborhood. We contacted Argentine ant expert Dr. Neil Tsutsui and here is what he said:

"The ants that you used to have in your yard were probably introduced Argentine ants (Linepithema humile). These are, by far, the most common ants in the Bay Area. A few native species of ants, such as the odorous house ant (Tapinoma sessile) pop up here and there, but they are generally less abundant and less widespread than Argentine ants in urban coastal California.

I've heard a few anecdotal stories of Argentine ant populations crashing (and disappearing) in locations where they were formerly quite abundant - both here in California and in other parts of their introduced range (like in New Zealand). Nobody really knows the cause, but it's an active area of research.

Overall, I would say that the absence of Argentine ants in your neighborhood is a good thing - less of a pest problem for homeowners, and their absence may present an opportunity for some of the native species to become re-established."

Best wishes,
Neil Tsutsui (Guest Expert), Corrie Moreau, & the AntAsk Team

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