Ants are common household pests. They don’t carry disease, but can be annoying.

Our most common household pest ant in the SF Bay Area, the Argentine ant, was found in a Stanford University study to invade houses most often during cold, wet weather.  These ants may simply be moving inside to escape the rain. If you are experiencing a large number of ants during or following a rain event, you may find that most will move back outside on their own when the weather dries up!

Argentine ants are the most common cause of ant invasions indoors, but other species may cause problems in this area. Knowing which ant is causing your issue is important, since different ant species have different food preferences and will take different types of bait. For ant identification and control information, contact the District laboratory at 650-344-8592.

If you see ants indoors, your first impulse will probably be to kill the ants that are inside, but don’t reach for the bug spray! Insecticide sprays aren’t usually needed for ant infestations. Instead, you can wipe up the ants with a damp soapy sponge, or even vacuum them up.

Next, you’ll want to stop additional ants from coming in. Clean up or remove whatever the ants are feeding on, then wipe away ant trails with soapy water. Entry points can be sealed with caulk to keep ants out.

In many cases, this is enough to stop the problem. If ants continue to invade, you may need to use an ant bait to kill the colony. Place bait stations near where you see ants entering. If one bait type seems not to work, try a bait with a different active ingredient (the active ingredient is listed on the front of the box).

Severe or persistent ant infestations may require the assistance of a professional Pest Control Operator (PCO). Professional pest managers often have access to tools and control materials not available to the general public. Visit our webpage to learn more about how to choose a Pest Control Operator.

For more information on ants, visit the UC IPM webpage.

Page last reviewed: January 9, 2023