A few weeks ago, with her son at school and her husband at work, Regina Rogers thought she was alone in her Carlsbad home.

But then she noticed three thick, black lines on her living room wall.

Moving lines.

Ants, Rogers realized, as she watched the procession fork and descend to the floor, then re-form a single line into the kitchen and disappear into the pantry.

"There were thousands of them. I was almost in tears," she recalled.

At this time of year, anyone could face an ant invasion, experts agree.

Tiny armies can strike fast, unexpectedly and with what seems like overwhelming numbers.

But people have a good chance of victory if they know how to fight back.

In Southern California, it's the dull-brown, common Argentine ant that launches the large-scale, indoor invasions as summer heats up.

"Hot, dry weather drives them inside. They come in looking for moisture, looking for food," said John Klotz, a UC Riverside-based ant control specialist.

Argentine ant populations also increase through the summer, Klotz said.

In spring and early summer, a colony's single queen lays eggs, and throughout the summer, larvae turn into young ants, which become workers that seek food for the colony and care for new eggs and larvae.

When Argentine ants find their way inside --- and almost any crack or crevice is a door -- they seek food and water and emit a pheromone, or a chemical secretion, to summon other ants when they find it, Klotz said.

Once the signal is sent, a single ant can quickly turn into thousands, even millions, all following the growing chemical scent trail, Klotz said.

And Argentine ants, unlike other species, form "supercolonies," cooperating with worker ants from nests other than their own.

"Your neighbor's ants are your ants," Klotz said.

Argentine ants don't bite or spread disease, but that hardly matters to most people.

"No one wants to eat food that ants have been crawling all over," said Jim Shaver, owner of Carlsbad-based Antbusters.

"And people find them all over the place, on baby cribs, in the shower," he said.

In one recent incursion, inch-wide lines of ants were flowing through light sockets in the home's ceiling, he said.

"It's a big problem here, especially this time of year when it gets really hot," said Jeff Gavitt of Temecula-based Black Knight Termite and Pest Control, which serves customers from San Diego County to San Bernardino. "We get calls all the time."

Rogers, the mother from Carlsbad, laughed as she described how she handled the uninvited guests: She sucked them up with a vacuum, nearly crying as she did the disgusting work.

Although Rogers acted from panic, using a vacuum to remove a trail of indoor ants is the correct first step, according to information published by UC Davis' Department of Agriculture and Natural Resources.

Another method recommended by Gavitt is to spray the ant trail with Windex or some other kind of ammonia-based cleaning product.

"It's nontoxic and has a better smell than most insecticides," he said. "Once the spray dries, you can wipe the ants away."

Experts suggest removing the source that is attracting the bugs, and using caulk or petroleum jelly to seal any entry points.

An ant problem is best solved by eliminating the colony, UC Davis experts said.

Ant baits are the best consumer-grade products available, and they should be placed outdoors, near suspected entry points.

When they work, the sweet bait mixed with slow-acting pesticides attract worker ants, which take the bait back to their colonies to feed others.

Ant baits are not usually recommended in the house, because they may draw the pests inside.

Sometimes people can't figure out how ants are getting into the house, and only see them pouring out of cracks in the wall, said Shane Hoy, a field representative with Escondido-based Pro Pacific Pest Control.

"People have ants in the house, and they're sure there's a colony living in their wall voids," Hoy said.

Although ants travel behind the walls, Hoy said that in his experience almost all of them are coming in from the outside, their colonies in soil or under rocks.

But Shaver disagreed, saying he finds many ants that establish indoor colonies.

He once traced a colony to a small box forming part of a window latch.

Either way, many companies use a commercial-grade, slow-acting insecticide that ants track back to the colony.

"Ants are very social animals," Gavitt said. "They groom each other, and that helps spread the poison back to their nest."

Experts agree that pest control companies have access to more effective treatments than most consumers, and if a problem persists, the homeowner may require outside help.

If ants are only outdoors, a professionally applied repellent barrier can keep them and other insects from coming in, said Sheri Kok. She and her husband own Escondido-based ARV Pest Control, which specializes in landscape pest control.

But if they do get inside, it's not a reflection on your housekeeping, she noted.

"Most people erroneously think that if they keep their homes clean enough, they won't have a problem," she said. "But they'll come in simply to cool off."

Call staff writer Sarah Gordon at 951-676-4315, ext. 3517.