Argentine Ants: The Bay Area's Most Persistent Pest

Why this one ant dominates

If you live in Mountain View or anywhere on the Peninsula and you have ants, the odds are overwhelming that they are Argentine ants. Introduced to the United States over a century ago, they have taken over California's coastal and valley regions by out-competing native ants entirely. The reason they dominate is their social structure. Unlike most ants, Argentine ant colonies do not fight each other. Instead they cooperate, forming enormous interconnected supercolonies with many queens that can stretch across entire neighborhoods. What looks like your ant problem is really one small edge of a colony that spans the block.

How supercolonies work

A single Argentine ant nest can hold multiple queens, and nests link together into a network that shares workers and resources. This is why the store-spray approach fails so reliably. When you spray a visible trail, you kill the foragers you can see, but the colony simply reroutes around the dead zone and keeps coming. You are bailing water without fixing the leak. The colony's size and resilience also mean they recover from partial treatment quickly, so anything short of hitting the colony itself buys you only a few quiet days.

The seasonal pattern in Mountain View

Argentine ants track water and weather, and Mountain View's Mediterranean climate gives them a clear rhythm. In the wet winter months, rain floods their outdoor nests and pushes them indoors and up onto the warm, dry slab of your home, which is why you see them along baseboards and the foundation edge after storms. In the dry summer, the opposite happens, their outdoor moisture sources dry up and they come inside chasing water at sinks, dishwashers and bathrooms. Homes near Stevens Creek, Permanente Creek and the Shoreline greenbelt feel this more, because the creek corridors are ribbons of continuous ant habitat.

What actually works

Because the colony is the target, baiting does most of the work in Argentine ant control. Slow-acting bait is carried back to the nest by foraging workers and shared with the queens and brood, which collapses the colony from the inside instead of just thinning the workers on your counter. This is paired with treating the exterior source, the foundation, entry points and landscaping routes, and with cutting off the moisture and food that draw ants indoors. It is slower than a spray on purpose, since spraying is the part that fails. See the ant control page for how treatment is structured.

What you can do yourself

A few habits reduce ant pressure between treatments. Wipe trails with soapy water to erase the scent path, though understand this is temporary. Store food in sealed containers, fix drips and standing water, and keep counters and pet-food areas clean. Outside, trim vegetation and mulch back from the foundation so ants have less shelter against the house, and address damp spots near the slab. These steps make your home less attractive, but for an established supercolony, they support professional baiting rather than replace it.

Sources and further reading: ipm.ucanr.edu.