The fastest way to kill ants in your house is with bait, not spray. Baits work because foraging ants carry poisoned food back to the nest, where it gets shared with the queen and the rest of the colony. Spray kills only the ants you can see, which represent a tiny fraction of the colony. To actually solve the problem, you need to eliminate the queen.
Why Bait Works and Spray Doesn’t
Ants feed each other mouth-to-mouth. When a worker finds food, she brings it back to the nest and passes it to other workers, larvae, and the queen. Slow-acting baits exploit this behavior. A worker picks up a small amount of bait, returns to the colony, and distributes the toxin before it takes effect. Over days, the poison spreads through the entire colony, eventually reaching the queen. Once the queen dies, the colony collapses.
Contact sprays and repellent insecticides do the opposite of what you want. They kill a handful of visible workers while alerting the rest of the colony to danger. For species like pharaoh ants, odorous house ants, and Argentine ants, spraying with a repellent insecticide can trigger “budding,” where the colony splits into multiple smaller colonies that scatter to new locations in your walls. You go from one ant problem to several. This is why entomologists consistently recommend baits over sprays for indoor ant control.
Pick the Right Bait for Your Ants
Not all ants want the same food, and using the wrong bait means they’ll walk right past it. The trick is matching bait type to species preference.
- Sweet baits (liquid or gel): Best for Argentine ants, odorous house ants, and carpenter ants, all of which prefer sugary foods. Argentine ants, the most common household ant in many regions, are attracted to sweet baits year-round.
- Protein or grease baits: Pharaoh ants and thief ants prefer fatty, protein-rich foods over sugar. If you set out a sweet bait and the ants ignore it, switch to a protein-based option.
- Oil-based baits: Fire ants respond best to baits containing oils.
If you’re not sure what species you have, set out both a sweet bait and a protein bait near an active trail and see which one the ants go for. Pavement ants, the dark brown ants you often see near foundations and sidewalks, will eat almost anything: sweets, proteins, or grease.
How to Identify Common Indoor Ants
You don’t need a microscope, just a rough sense of size, color, and behavior. Argentine ants are about 1/8 inch long, dull brown, and travel in wide, busy trails. Odorous house ants are similar in size but darker, and they give off a strong rotten smell when you crush them. Pharaoh ants are tiny (1/16 inch), yellowish-orange, and often found near kitchens or bathrooms.
Carpenter ants are the giants. Workers range from 1/4 to 1/2 inch, are black or red-and-black, and leave behind piles of fine wood shavings (called frass) near their nests. They don’t eat wood like termites do. They excavate it to build galleries for nesting. Finding sawdust-like debris near door frames, window sills, or baseboards is a strong sign of a carpenter ant colony. Carpenter ants require a different approach than most species, covered below.
Setting Up Baits Effectively
Place bait stations directly along ant trails or at the point where ants are entering your home. Resist the urge to clean up the trail first. You want the ants to find the bait and keep recruiting nestmates to collect it. Don’t spray insecticide anywhere near your bait stations, because repellent chemicals will keep ants away from the bait and defeat the purpose.
Most commercial baits use active ingredients like boric acid, indoxacarb, or fipronil at very low concentrations. Indoxacarb is particularly effective because it only becomes toxic after enzymes in the ant’s gut activate it, which makes it slow-acting enough to spread through the colony before killing anyone. Fipronil in protein-based baits targets queens and larvae directly, since they consume most of the colony’s protein.
Keep bait stations stocked and in place for at least two weeks. Most baits are slow-acting by design. You may see more ants in the first day or two as workers recruit others to the bait source. That’s a good sign. It means the colony is feeding heavily and distributing the toxin. Full colony elimination typically takes one to three weeks depending on colony size.
A Simple DIY Bait Recipe
If you’d rather not buy commercial bait, a homemade borax solution works well for sugar-loving species. The University of Hawaiʻi recommends this recipe: dissolve 1 teaspoon of boric acid powder and 3 tablespoons of white sugar in 1¾ cups of warm distilled or bottled water. Stir until fully dissolved.
Soak cotton balls in the solution and place them in shallow containers (jar lids work fine) along ant trails. The concentration is low enough that workers survive long enough to carry the solution back to the nest, but high enough to kill the colony over time. Replace the cotton balls every few days as they dry out. Use distilled or bottled water rather than tap water, as chlorine can reduce the bait’s effectiveness. Keep this solution away from children and pets.
Using Diatomaceous Earth as a Barrier
Food-grade diatomaceous earth (DE) is a powder made from fossilized algae. Under a microscope, the particles have sharp edges that cut through the waxy coating on an ant’s exoskeleton. Once that coating is breached, the ant dehydrates and dies. It’s a mechanical kill, not a chemical one, which means ants can’t develop resistance to it.
Apply a thin, barely visible layer along baseboards, window sills, cracks, and any entry points where you’ve seen ants. You can also dust it behind electrical outlets and switch plates using a small duster. Outside, spread a light band around your home’s foundation, extending 6 to 12 inches out. Check treated areas after 24 to 48 hours to see if ants have found an alternate route and reapply as needed.
DE works best as a supplemental barrier, not a standalone solution. It only kills ants that walk through it and does nothing to reach the queen inside the nest. Pair it with baiting for the best results.
Handling Carpenter Ants
Carpenter ants are a structural concern because they hollow out wood to nest in it. Look for sawdust piles near baseboards, door frames, hollow doors, or window frames. You can sometimes hear them inside walls: tap on the area and listen for a rustling or crunching sound as the disturbed colony moves around.
To locate outdoor nests, inspect large trees within about 30 feet of your home starting 15 to 20 minutes after sundown. Shine a flashlight up and down the trunk. If a nest is present, you’ll see ants streaming up and down. They also create visible trails through grass between their nest and food sources.
Indoor carpenter ant nests are best treated with insecticidal dust applied into wall voids through small drilled holes (1/8 inch) or through gaps behind electrical plates and under window sills. Apply just enough to leave a thin film. Never use liquid insecticides inside wall voids, as they can damage drywall, insulation, and wiring, and create a fire or shock hazard near electrical components. For large or hard-to-reach infestations, carpenter ants are one of the cases where professional help is genuinely worth the cost.
Cutting Off Entry and Food Sources
Baiting solves the immediate colony, but preventing reinfestation means eliminating what attracted ants in the first place. Ants enter homes looking for food and water, and they leave invisible chemical trails that guide other ants to what they find.
Seal cracks and gaps around windows, doors, pipes, and where utility lines enter the house with caulk or weatherstripping. Clean up food residue on counters and floors daily, especially sticky spills and sugary crumbs. Store pet food in sealed containers rather than leaving bowls out overnight. Fix leaky faucets and pipes, since many ant species nest near reliable water sources. Trim tree branches and shrubs that touch your house, as these serve as bridges for ants traveling from outdoor nests.
After you’ve eliminated a colony with bait, wipe down former ant trails with soapy water to remove the pheromone signals. Otherwise, scouts from nearby colonies may follow the old trail right back into your kitchen.