The most effective way to kill small ants is with bait, not spray. Baits work because foraging ants carry poisoned food back to the nest and share it with the queen and the rest of the colony. A spray kills the ants you can see, but the colony (which can number in the tens or hundreds of thousands) keeps producing more. Bait eliminates the source.
Why Bait Works Better Than Spray
Worker ants have a built-in food-sharing system. When a forager finds something to eat, she brings it back to the nest and passes it mouth-to-mouth to other workers, larvae, and the queen. This process distributes the toxic ingredient throughout the colony before ants start dying. That’s why the active ingredient in any good ant bait is slow-acting: if it killed ants on contact, foragers would die before making it home.
Spraying ants with a contact killer does the opposite of what you want. It wipes out the visible trail but leaves the colony intact. Worse, some species respond to the disturbance by “budding,” where a portion of the colony splits off with a new queen and sets up a second nest elsewhere in your home. Pharaoh ants are especially notorious for this. A single misguided spray can turn one colony into several.
Identifying Your Small Ants
Most tiny ants found indoors fall into a few common species, and knowing which one you have helps you choose the right bait. Odorous house ants are one of the most common. They’re dark brown or black, about 1/16 to 1/8 inch long, and give off a rotten coconut smell when crushed. They love sweet foods. Argentine ants look similar but form massive supercolonies with multiple queens, and they also prefer sweets. Pharaoh ants are even smaller, pale yellow to light brown, and are found frequently in kitchens and bathrooms.
The distinction matters most with pharaoh ants. Because they bud so aggressively when disturbed, sprays and even some conventional baits can backfire. Products containing insect growth regulators are the most reliable option for pharaoh ants. These work by making the queen sterile and disrupting the colony’s ability to produce new queens, so even if a few ants scatter, they can’t rebuild.
Best Active Ingredients for Small Ants
Commercial ant baits use a handful of proven active ingredients: boric acid (borax), fipronil, avermectin, and hydramethylnon. For small sugar-loving ants like odorous house ants and Argentine ants, liquid or gel baits containing borax tend to be the most effective because they mimic the sugary foods these species prefer.
The most widely available liquid bait uses sodium tetraborate decahydrate (borax) at a 5.4% concentration mixed into a sweet liquid. At that low concentration, worker ants consume the bait and survive long enough to carry it deep into the nest. For severe Argentine ant infestations, the UC Integrated Pest Management Program recommends liquid borate baits in refillable stations, ideally at 0.5% to 1% borate in sugar water.
Fipronil-based gel baits are another strong option, particularly for ants that prefer protein or grease over sugar. If you set out a sweet bait and ants ignore it, switching to a protein-based bait with fipronil often does the trick. Some ant species shift their dietary preferences seasonally, so what works in spring may not work in late summer.
How to Make a DIY Bait
You can make an effective liquid ant bait at home with three ingredients. Mix 1 teaspoon of boric acid powder with 3 tablespoons of white sugar, then add warm distilled or bottled water up to 1¾ cups. Stir until everything dissolves completely. Avoid tap water, as chlorine and minerals can affect the mixture. Soak cotton balls in the solution and place them along ant trails, near entry points, or wherever you’ve seen activity.
The key is keeping the boric acid concentration low. Too much kills foragers before they share the bait. Too little won’t affect the colony. The ratio above keeps the concentration under 1%, which is the sweet spot for colony elimination. You’ll likely see increased ant activity around the bait for the first day or two. That’s a good sign: more ants feeding means more poison reaching the nest. Resist the urge to spray them. Full colony die-off typically takes one to two weeks.
Placing Bait Effectively
Put bait stations directly on or next to active ant trails. Small ants follow pheromone paths along edges, so check baseboards, windowsills, the gap between your countertop and backsplash, and under appliances like the dishwasher and refrigerator. If you can find where ants are entering from outside, place bait on both sides of that entry point.
Don’t clean up ant trails while baiting. Those pheromone paths are guiding more foragers to your bait. Once the colony is dead and ant activity stops (usually within 7 to 14 days), then clean the trails with soapy water to remove the chemical scent. Also remove competing food sources during this period. Wipe down counters, seal food in airtight containers, and take out trash regularly. You want the bait to be the most attractive option in the room.
Diatomaceous Earth as a Non-Toxic Option
If you’d rather avoid chemical baits entirely, food-grade diatomaceous earth kills ants through a mechanical process. The powder is made of microscopic fossilized algae with razor-sharp edges. When ants crawl through it, the particles scratch their exoskeleton, causing them to lose moisture and die from dehydration.
Sprinkle a thin, even layer along ant trails, around entry points, and in cracks where you’ve seen activity. A light dusting is more effective than a thick pile, since ants will walk around a heavy mound. Reapply every few days indoors, and vacuum up the old layer before putting down fresh powder. The main limitation of diatomaceous earth is that it only kills ants that physically contact it. It won’t spread through the colony the way bait does, so it works best as a barrier or supplement rather than a standalone solution for a large infestation.
Safety Around Kids and Pets
Boric acid is low in toxicity for adults if accidentally ingested in small amounts, but infants and small children are significantly more sensitive. Symptoms of boric acid ingestion include nausea, vomiting, and stomach pain. In infants exposed to larger amounts, seizures and serious neurological effects have been reported. The EPA does not classify boric acid as a likely carcinogen, but that doesn’t make it safe to leave within reach of curious toddlers or pets.
Animals show similar poisoning symptoms, which can start within two hours of ingestion. Place bait stations in spots children and pets can’t access: behind appliances, inside cabinets, or in enclosed bait stations that allow ants to enter but keep small fingers and paws out. If you’re using a DIY liquid bait on cotton balls, tuck them behind the refrigerator or under the stove rather than leaving them on the counter. Getting down to floor level after placing baits helps you spot anything a crawling baby or a curious dog could reach.
Food-grade diatomaceous earth is the safest option around pets and children. It’s non-toxic if ingested in small quantities, though you should avoid creating dust clouds when applying it, since inhaling fine particles can irritate the lungs.