Ants often enter buildings seeking food and water, warmth and shelter, or refuge from dry, hot weather or flooded conditions. They may appear suddenly in buildings if other food sources become unavailable or weather conditions change.
One such ant we see headed indoors during rainy conditions in California, is the Argentine ant. The Argentine ant is about 1/8 of an inch long and dull brown in color. It's normally found living in the landscape in shallow nests, and might even be living just outside your building. When rainy weather floods their nest, Argentine ants may use your home or office as a warm and dry place to relocate.
This rainy season, before ants have a chance to invade your home, be proactive and “ant-proof” your buildings ahead of time Determine what the ants are attracted to and eliminate the food or water source. Monitor the places in and around your home where ants are often found. Follow ant trails to find where they are entering, and seal them off using caulking or other sealants.
Of the 270 species of ants in California, fewer than a dozen are pests, and although ants can be bothersome pests indoors, it's important to remember that outdoors they sometimes also play a beneficial role in the environment.
Visit the Ants section of UC IPM's home and landscape web pages for more information about preventing or managing ant invasions. There you will find videos about ants including, “What to do if you have an ant emergency” and “Why do ants invade?” as well as other resources to help identify ants and know what to do indoors or out.