How to get rid of ants in your home

They can’t help it, that trail of ants crawling up a kitchen cabinet. The determined critters head inside to escape the cold, wet winter days or hot, dry summer conditions. But our sympathies don’t extend to safe harboring ant armies. And we also aren’t happy to see them in the garden keeping aphids alive.

There are 12,400 ant species in the world, of which 270 of them live in California.

The most common is the Argentine ant, Linepithema humile. A second less common but important species is the carpenter ant, Camponotus species. Carpenter ants don’t eat wood like termites; however, they hollow it out to nest in and thus cause damage inside.

Ant biology and behavior have long inspired science projects and allegories. But what we want to know is how to deal with these space invaders.

Outside, ants are beneficial insects. They recycle nutrients, aerate the soil and feed on fleas, termites and other pests in the garden. But when they help aphids, mealybugs and scale insects survive, they are garden pests. Inside, they are simply unwelcome.

Whether you want to eliminate ants in your house or control them in your garden, the basics are the same: remove access, resources and nesting sites.

In your home

First, know what you’ve got. All ants differ from termites in three main ways: Ants have tiny waists, hind wings smaller than front wings and front antennae with elbows. Termites have broad waists, equally sized wings and straight front antennae. Argentine ants are about 1/8-inch-long and dull brown. Carpenter ants are 1/4- to 1/2-inch-long, black or black and red.

Breathe a sigh of relief if you have ants, not termites. You can vacuum the ant trails or wipe them up with soapy water and spray with window cleaner to eliminate them and wash away their scent trail. These techniques work better than insecticide sprays and leave no residual toxicity.

Look for ant nests in potted plants. Take infected pots outside, submerge them in a solution of 1 to 2 tablespoons of insecticidal soap per quart of water, and allow the solution to cover the soil for 20 minutes or more.

Remove whatever attracted the ants. Mop, scrub and remove trash. Store food items, including pet food, in closed containers. Fix leaky faucets; they attract thirsty ants.

Then, discover the entry points. Eliminate caulk holes, crevices or cracks in foundations or walls by caulking openings or plugging them with petroleum jelly.

Ants are outdoor critters, so although you can eliminate them inside if you want to keep them out, you need to take action outside.

In the garden

Focus on removing or managing food sources, including aphid-infested bushes or trees with ripened fruit near your house. Eliminate nearby nesting spots by moving plants and mulch at least a foot from the foundation or even farther to be fire-smart.

If that doesn’t stop the invasion, and if you’re concerned about aphids, mealybugs and scale insects, consider using slow-acting bait stations or gel bait outside. These pesticides don’t work immediately; you’ll likely need to continue wiping up scouts and trails inside for a few days until the worker ants have taken the bait to the colony. But baits are the only type of insecticide recommended in most situations and are the safest and easiest to use. Use them indoors only for a very serious infestation, and keep in mind they could attract outside ants inside. Instead, place baits outdoors near ant trails and nest openings.

Look for Argentine ant nests in shallow mounds and carpenter ant nests in tree stumps and other wood with sawdust-like frass deposits nearby.

It’s unrealistic and impractical to attempt to totally eliminate ants outdoors, though. Instead, focus on excluding ants from buildings or valuable plants. And remember — ants can be annoying, but they can also play a beneficial role in the garden.

Sponsored by UC Cooperative Extension, the University of California Marin Master Gardeners provides science- and research-based information for Marin home gardeners. Email questions to helpdesk@marinmg.org. Attach photos for inquiries about plant pests or diseases. Please call 415-473-4910 to see when a master gardener will be at the office or drop off samples 24/7 in the sample box outside the office. To attend a gardening workshop or subscribe to Leaflet, a free quarterly e-newsletter, go to marinmg.ucanr.edu.