Who are Those Ants in Our Homes and Gardens?

Lots of people in the L.A. area have been complaining about the heat. Over the last week, cities in our region have been experiencing temperatures well into the 90s. On Monday, Woodland Hills reached 108 degrees!

Whenever the temperature rises like this, I start to notice ants indoors. Only this morning during our Nature Lab meeting, I found a trail of ants leading to the sink, and another leading to the snack shelf.

The ants I found are Argentine Ants, Linepithema humile. They are an introduced species from South America (Argentina and Brazil) and are now considered the most common ant in our area. According to the Insects of the Los Angeles Basin book, these ants were "introduced to New Orleans before 1891 in coffee shipments from Brazil, and it has since spread rapidly over much of the United States."

This is what the same book has to say about their pest status:

"The species is one of the most persistent and troublesome of all our house-infesting ants. Argentine Ant workers seek out and feed on almost every type of food, although they are especially fond of sweets. Making themselves most objectionable, the ants invade the house through minute crevices and cracks—filing along baseboards, across sinks, and over walls and tables in endless trails."

How do you feel about ants in your home? While writing this blog, I've found it interesting to ponder this question. As you may have noticed I am a nature lover, however I am definitely not a fan of ants in my house and will go to great lengths to remove them. Many times this feels like a losing battle, especially because I'm not one for spraying pesticides all over the place I live.

Argentine Ant about to take drink of water in our Nature Lab trailer

(It is one eighth of an inch long)

The Argies, as we "fondly" refer to them, have also been found throughout the North Campus. This isn't surprising as it is well documented that this ant species has displaced many of our native ants. According to Alex Wild, author of the Myrmecos ant blog, Argentine Ants, "can drive native arthropods to extinction, instigating changes that ripple through ecosystems. In California, horned lizard populations plummet. In South Africa, plant reproduction is disrupted. Worldwide, the Argentine Ant is a persistent house and crop pest. This is not a good ant." Here are some pictures of their activities on the North Campus:

Argentine Ants killed all the paper wasps in this nest

Argentine Ants tending citrus scales in our orange trees

When I found the ants had killed all the paper wasps in the nest pictured above, I have to admit I was disappointed. I know many would be cheering for the ants, as paper wasps are viewed as a pest themselves. However, I had already become invested in the livelihood of that particular wasp nest and would check up on it every time I was out in the gardens. I find it infinitely interesting to ponder our notion of pest. What is acceptable in some circumstances is unacceptable in others. However, I still haven't come across anyone who is a fan of Argentine Ants!

Need tips of managing ants in your home? Check out the UC Davis Integrated Pest Management website.