Probably the most common ant in southern California and on the Central Coast is the Argentine ant. The workers are light to dark brown, about one eighth inch long and are usually seen running along in columns from their nests to sources of food and back. The nests may be established almost anywhere, but are often found next to sidewalks, along retaining walls and house foundations where soil and moisture conditions are favorable. As fall comes and cold, rainy weather begins, the ant problems will probably get worse as the ants seek a warmer, dryer place to spend the winter. Argentine ants are very quick to relocate if their nest is threatened by water or excessive soil disturbance. But they will also come back very quickly when the problem condition subsides. Worker ants and scouts are continually investigating their surroundings for sources of food and desirable nesting sites.
The bottom line is that an ant problem is not going to go away over night, no matter what you do. Ant management (note I did not say control) requires a sustained, committed effort, first to reduce the population and then to keep it suppressed to acceptable levels.
When you find ants in the house, you should observe the columns and try to find out where they are coming in. No house is ant-proof. There are cracks around windows and doors. There are slits between the walls and foundation. Argentine ants can exploit a crack smaller than one thirtieth of an inch. When the entry point is located, go outside to see if you can find the outside extension of the column. Also, look for nest sites along and near the foundation of the house. Entry points can be plugged with chalking or putty. The columns inside the house can be sucked up with a vacuum cleaner. By the way, the food source which has attracted the ants, usually sweets or a sweet product of some kind, should be stored in glass jars with tight lids or plastic ware, which can be tightly sealed.
The nest sites outside should be treated with an “ant bait”-type material. Spraying ants is only a very temporary fix. Sprays kill the ants you see, but they do not kill out the nest or the queen(s), which are continually producing eggs that quickly replace the workers that have been exterminated. Place the bait at and around the nest sites. Also treat the area along and near the house foundation with bait, so nests you do not find are being treated. Renew the bait treatments two to three times per year, even after ant activity appears to subside.
If you use this approach to ant control, you should see a marked decrease in ant activity in a year or two.