Why Argentine Ants Invade During a Sacramento Summer

Why do Argentine ants come inside in a Sacramento summer?

They come for water. Sacramento has about 18 inches of rain a year and almost none from June to September. In that dry stretch, UC IPM says ants often search homes for water, including bathroom faucets and drains. The colony is usually outside; the trail you see indoors is a supply line.

It is tempting to think ants invade because the kitchen is dirty. In dry weather the stronger driver is water. Sacramento's summer is long and rainless, with average highs of 87 F in June, 92 F in July and 91 F in August, and the soil near foundations, sidewalks and driveways dries out. A UC San Diego research summary says that in August and September, when California was too dry for them, the ants' quest for water led them to bathrooms and kitchens.

That explains a pattern many Sacramento households notice. The ants are quiet in the wet winter, begin to appear in late spring, and become a daily nuisance by August. A dripping bathroom faucet, a sink drain, a pet water bowl and a condensate line from an air conditioner all become destinations. The same colony that was outdoors in March is trailing across the counter in August because the places it used to drink from have dried up.

The Sacramento pest calendar shows where this sits in the wider year, alongside drywood termite swarms in August and yellowjacket colonies growing through summer.

What do Argentine ants look like and where do they nest?

Argentine ants are about 3 millimeters long, dark, and do not sting. UC IPM calls them the most common outdoor ant in California. Nests are normally in moist soil, under debris or along sidewalks and driveways, and workers travel up to 100 feet to find food, water and shelter inside buildings.

The identification clues are habit, not size alone. Argentine ants follow trails, and the trail is the clue. When you find one, you are looking at the path between a nest and a resource, whether that is a faucet, a pet bowl or a crumb on the counter.

UC Riverside's Center for Invasive Species Research notes that Argentine ants have colonized riparian woodland in Yolo and Solano counties. For Sacramento County, that matters because the American and Sacramento rivers, the Parkway and creek corridors such as Arcade Creek and Morrison Creek offer shaded, moist ground. It does not mean that every neighborhood near a river has a worse problem, only that the species is established in this region.

Where nests are close to the house, the distance workers travel shrinks. A planter bed against a wall, a pile of leaves beside the foundation, a stack of pavers or a sprinkler leak at the base of a wall are the places to look. If the nest is on a neighbor's property or in a shared landscape strip, you may never find it, which is another reason treatment aims at the trail and the baits, not at locating every nest.

Why does spraying the trail not solve it?

A spray kills the workers you can see, but the nest keeps producing more. UC IPM instead recommends slow-acting liquid baits with 1 percent or less borate, which workers carry back to the nest. Baits work because they are taken home, not because they kill on contact.

Think of the ants on your counter as a small fraction of the colony. The queens and most of the brood are in the nest, wherever it is. Wiping or spraying the visible trail does nothing to that supply, and another group of workers arrives in a day or two. Interrupting the trail does not remove the cause.

Bait is different. UC IPM's guidance is liquid bait containing 1 percent or less borate, placed in a dispenser on each side of the house at least 5 feet from nests. The low concentration is deliberate: workers feed on it and carry it back, and it works slowly enough that they spread it through the colony before they die. Bait stations that are refilled and left in place often need to stay out for a while, which is why a technician may come back for a second look.

A technician working on an ant job also follows the product label, and the price is explained and approved before treatment begins. See the ant control page for what a visit involves and the pest control cost guide for published ranges, including HomeAdvisor's $80 to $500 for ant extermination. Those are national figures, not Sacramento quotes.

What can you do yourself before a technician arrives?

Remove the water and the shelter. Fix drips, seal food, caulk entry gaps and prune plants away from the house. These steps match UC IPM's management list and cost little. They reduce the reason ants come inside, which makes any bait or treatment more effective and makes the problem less likely to return next summer.

Start with water, since that is what brings ants indoors. Check under bathroom and kitchen sinks, around faucets and drains, near the water heater and anywhere a condensate line drips. Empty plant saucers, and consider moving a pet water bowl away from the wall. Outside, look at sprinkler heads and hose bibs near the foundation.

Next, take away easy shelter. Rake leaves and debris away from the foundation, move woodpiles and pavers, and prune shrubs, vines and tree limbs so they do not touch the house. These plants are bridges, and ants use them to reach windows and eaves. Ivy against a wall is a particular favorite for ants and, as UC IPM notes, for roof rats, which is the subject of our guide to roof rats in Sacramento attics.

Finally, close the gaps and seal the food. Caulk around pipes, window frames, door thresholds and cracks in the foundation. Keep sugar, honey, pet food and ripe fruit in sealed containers, and wipe spills quickly. None of this guarantees the ants will stay away, but it removes most of what attracts them.

One small caution: avoid spraying the baits' trail. If you have baits in place, leave the trail alone, because killing the workers that are feeding defeats the purpose.

• Fix dripping faucets, sink drains, condensate lines and sprinkler leaks
• Store sugary food, pet food and ripe fruit in sealed containers
• Caulk gaps at pipes, window frames, door thresholds and foundation cracks
• Prune plants so no branch or vine touches the house
• Rake debris and move woodpiles or pavers away from the foundation

What does a technician do for an ant problem?

A technician looks for the trail, the entry points and the likely nest areas, places liquid bait where UC IPM recommends it, treats entry gaps, and explains what you can change in the yard. The price is explained and approved before treatment starts, and a written service report follows the visit.

The visit typically starts with questions: where do you see them, at what time of day, since when and what have you tried. The technician then walks the outside of the house, looking at the foundation edge, planter beds, irrigation lines, trees and fences, and checks the inside at the kitchen, the bathrooms and wherever the trail enters. Products are applied per the label.

Because the colony is usually outside and may extend beyond your lot, the treatment plan often combines baits, perimeter work and changes to the landscape. The technician may ask you to leave baits in place and not wipe the trail. If ants are in a wall void or a crawl space, the visit may also touch on crawl space pest control.

To ask about a visit, call (855) 974-4733. The phone is answered 24/7, and most calls are scheduled the same day when a technician is available, though no particular arrival time is promised. Sacramento Pest Control connects callers with an independent licensed local pest-control company, and that company does the work.

Why do the ants come back, and how is Sacramento different?

Colonies are large, nests are often shared across property lines, and the dry months return every year. UC IPM notes that ants often search homes for water in hot, dry weather, so each Sacramento summer recreates the same pressure. Consistent water control, sealing and bait use before August reduce the odds of a repeat.

A single successful treatment can clear a trail, but it cannot change the weather or a neighbor's landscape. Argentine ants are well established across California, and Sacramento's dry summers renew the drive indoors every year. Older neighborhoods with mature landscaping, such as Land Park, Curtis Park and East Sacramento, offer plenty of shade, irrigated beds and foundation plantings. Newer tract areas have irrigated strips and landscape beds against the house, and the same principle applies.

That is why many households benefit from acting in late spring. Put baits out before the soil dries, fix the leak you noticed in March, and trim plants away from the walls in May. You are not preventing every ant. You are making your house a less rewarding place to visit than the next one.

If ants are not the only concern, compare notes with the other pests that follow the same dry-season pattern. Drywood termites swarm from August, and yellowjackets scavenge in September, so a late-summer visit is a chance to ask a technician to look at more than the kitchen. The pest control page explains a general visit.