Both borax and boric acid kill ants effectively, and for practical purposes, they’re nearly interchangeable in DIY ant baits. They share the same active element (boron), work through the same mechanism, and perform best at similar low concentrations. The real differences come down to availability, form, and a few safety nuances worth knowing before you mix up a batch.
How They’re Related
Borax (sodium tetraborate decahydrate) is a mineral salt of boron. Boric acid (orthoboric acid) is a refined, slightly more concentrated form of the same element. You can think of borax as the raw material and boric acid as a processed version with a higher percentage of boron by weight. A 5% borax solution delivers roughly the same amount of active boron as a 6% boric acid solution. In ant baits, this difference is small enough that either one works.
Borax is the white powder sold in the laundry aisle (20 Mule Team is the most common brand). Boric acid is typically sold as a fine powder at hardware stores or pharmacies, often already labeled for pest control. Both have been registered as pesticides in the U.S. since 1948, and the EPA classifies boric acid as showing “evidence of noncarcinogenicity” for humans.
How They Kill Ants
Both borax and boric acid are stomach poisons. When ants eat bait containing either compound, the boron disrupts their digestive system and eventually kills them. The key advantage over contact-kill sprays is that worker ants carry the bait back to the colony and share it with nestmates, including the queen. This is what makes boron-based baits capable of wiping out entire colonies rather than just the ants you can see.
The critical factor isn’t which boron compound you use. It’s the concentration. Too much, and ants die before they make it back to the nest. Too little, and the colony shrugs it off. Research from the University of California, Riverside found the effective range for boric acid in liquid sugar baits is 0.5% to 3.7%. Anything above 5% kills foraging ants too quickly, cutting off distribution to the rest of the colony. The sweet spot for Argentine ants (one of the most common household species) is a 25% sugar water solution with 0.5% to 3.6% boric acid.
The Best DIY Bait Recipe
The simplest and most widely recommended liquid bait uses three ingredients:
- 1 teaspoon boric acid powder (or borax)
- 3 tablespoons white sugar
- 1¾ cups warm distilled or bottled water (tap water can introduce minerals that affect the mix)
Stir until everything dissolves completely. Pour the mixture into small containers like condiment cups and tuck a cotton ball inside so ants can climb in and feed without drowning. Place the stations along ant trails or near entry points where you’ve seen activity.
This recipe lands right in that effective low-concentration range. The sugar draws ants in, and the low boron dose means they survive long enough to bring the poison home. You’ll need patience: it can take one to two months of continuous baiting to collapse a colony. Check stations weekly and replace any that get moldy or dry out.
One important caveat: this recipe targets sugar-feeding ants. Many common species, including Argentine ants and odorous house ants, love sugar baits. But carpenter ants, pharaoh ants, and big-headed ants sometimes prefer protein or grease, especially at certain times of year. If ants ignore your sugar bait entirely, you may need to identify the species and switch to a protein-based bait (peanut butter mixed with borax works for grease-loving species).
Which One to Buy
If you’re choosing between borax and boric acid for a DIY ant bait, go with whichever is easier to find. Borax is sold at most grocery stores. Boric acid is more common at hardware stores and online retailers. Both dissolve in water, though boric acid dissolves a bit more readily since it’s a finer powder.
For dry applications (dusting into wall voids, cracks, or behind appliances), boric acid powder is generally the better choice. It’s lighter and clings to surfaces more easily. Borax crystals are coarser and don’t spread as evenly in tight spaces. If you’re making liquid bait, it genuinely doesn’t matter which one you use.
Safety Around Pets and Children
Both compounds are classified as low in acute toxicity, but “low toxicity” doesn’t mean harmless, especially for small bodies. The estimated lethal dose of boric acid for an adult human is 5 to 20 grams, but for children it drops to 3 to 6 grams, and for infants, less than 5 grams. Even small, non-lethal exposures in infants have caused vomiting, diarrhea, skin irritation, and nervous system effects.
Dogs appear more sensitive to both compounds than rodents used in lab studies. Signs of poisoning in pets include excessive drooling, vomiting (sometimes with a blue-green color), fever, loss of appetite, and diarrhea. In large exposures, tremors and seizures can occur. Young and elderly animals are more vulnerable than healthy adults.
There’s one notable safety difference between the two: borax is significantly more irritating to eyes. The EPA places borax products in Toxicity Category I (the highest) for eye irritation, while boric acid rates as only mildly irritating. If you’re handling borax powder, avoid touching your face, and keep the box away from kids.
For households with pets or young children, place bait stations in areas they can’t reach: behind refrigerators, inside closed cabinets, under heavy furniture. The concentrations used in ant baits are very low, but a curious toddler or dog lapping up sugar water repeatedly could accumulate a problematic dose over time. Any visible powder left on floors or carpets after a dry application should be brushed into cracks or swept up before letting pets and children back into the area.
Why Low Concentration Matters More Than the Compound
The most common mistake with boron-based ant baits is using too much. It’s natural to think that a stronger mixture will work faster, but the opposite is true. A bait with 5% or more boric acid acts more like a contact killer: it knocks out the foragers but never reaches the queen or the brood deep inside the nest. Within days, the colony produces new foragers and the problem comes right back.
Baits in the 0.5% to 1.0% range are the most effective at penetrating an entire colony, though they require consistent baiting over weeks. Think of it as a slow, colony-wide poisoning rather than a quick kill at the surface. Keep bait stations stocked, resist the urge to add more powder, and give the process time to work. If you haven’t seen a significant reduction after two months, the species may need a different bait type or professional treatment.