Borax is one of the most effective and inexpensive ways to kill an entire ant colony, not just the ants you can see. Mixed with sugar and water, it works as a slow-acting poison that foraging ants carry back to the nest, where it spreads to the queen and the rest of the colony. You can expect to see results within 24 to 48 hours, with full colony elimination taking up to two weeks.
How Borax Kills Ants
Borax disrupts an ant’s stomach and nervous system once ingested. The key is that it works slowly enough that foraging ants don’t die at the bait station. Instead, they carry the poisoned food back to the nest and share it with other workers, larvae, and the queen through a process called trophallaxis (essentially mouth-to-mouth feeding). This chain of sharing is what makes borax so effective: it turns the colony’s own food distribution system into a delivery mechanism for the poison.
If the concentration is too high, worker ants die before making it back to the nest, and you’ve just killed a handful of ants while the colony replaces them within days. That’s why getting the ratio right matters more than anything else.
The Best Borax Bait Recipe
The University of Hawai’i’s College of Tropical Agriculture recommends this liquid bait formula:
- 1 teaspoon borax (or boric acid powder)
- 3 tablespoons white sugar
- 1¾ cups warm distilled or bottled water (not tap water)
Stir until everything dissolves completely. Pour the mixture into small containers like condiment cups, and place a piece of cotton ball or paper towel inside to give the ants something to walk on and drink from. Set the stations wherever you’re seeing ant activity.
This recipe keeps the borax concentration around 1%, which is low enough that ants feed freely and survive long enough to bring it home. Commercial products typically use 4 to 6% borax, which works over a 14 to 21 day window. The lower your concentration, the longer it takes, but the more thoroughly it penetrates the colony.
Check your bait stations weekly and replace any that look moldy or dried out. Be patient. The University of Hawai’i advises allowing ants to feed for up to one or even two months for large or persistent colonies.
Sugar Baits vs. Protein Baits
A sugar-based borax bait works well for the most common indoor species: odorous house ants, pavement ants, and the small dark ants typically called “sugar ants.” These species are naturally drawn to sweet foods, so the sugar does the job of luring them in.
Carpenter ants and some other species prefer protein or fat over sugar. If you set out a sugar bait and ants ignore it, switch to a peanut butter mix. Combine about one tablespoon of peanut butter with half a teaspoon of borax, and place small dabs of it near ant trails. You can also try both types of bait simultaneously to see which one gets more traffic. Ant dietary preferences shift seasonally too. A colony that craves sugar in spring may prefer protein in late summer when they’re raising more larvae.
Borax vs. Boric Acid
Borax (sodium tetraborate) and boric acid are closely related boron compounds, and both kill ants through the same mechanism. They aren’t identical, though, and each has practical advantages.
Boric acid dissolves more easily in water, making it better for liquid bait stations. It also holds up well in humid environments without losing potency. At concentrations of 5 to 8%, boric acid formulations can achieve 85 to 91% colony mortality within 7 to 10 days. The trade-off is that boric acid has a slightly acidic taste that can deter some ants from feeding.
Borax mixes more easily with sugar and other food attractants because its taste is milder. It works more slowly, typically reaching 80 to 87% efficacy over 14 to 21 days, but that slower action can actually help with colony penetration since more workers survive to share the bait. Borax also tends to absorb moisture from the air, so dry borax powder applications may clump or crystallize in humid conditions.
For most home use, regular borax from the laundry aisle (like 20 Mule Team Borax) works perfectly well. You don’t need to seek out technical-grade boric acid unless you’re making liquid baits in a very humid climate.
How Long It Takes to Work
You’ll typically notice fewer ants within 24 to 48 hours of setting out bait. That doesn’t mean the colony is dead. What you’re seeing is the initial wave of foragers dying off after carrying poison back to the nest. Complete eradication, where no new ants appear, generally takes one to three weeks depending on colony size.
A small colony of a few hundred ants might collapse within a week. A mature colony with tens of thousands of workers and multiple queens can take the full two months that researchers recommend keeping bait stations active. If you’re seeing a steady stream of ants at the bait station, that’s actually a good sign. It means the bait is attractive and being carried back to the nest. Resist the urge to kill the ants at the station or move it. Let them feed.
Keeping It Safe Around Kids and Pets
Borax has relatively low acute toxicity compared to most pesticides. The lethal dose in rats is around 4,500 to 5,000 mg per kilogram of body weight, placing it in the EPA’s “low toxicity” category. But low toxicity isn’t no toxicity, and the numbers are different for smaller bodies.
For humans, the estimated minimum lethal dose is 5 to 20 grams for adults, 3 to 6 grams for children, and less than 5 grams for infants. To put that in perspective, a teaspoon of borax weighs roughly 5 grams. Dogs appear to be more sensitive to boron compounds than rodents, so even smaller amounts could cause problems for a pet.
Signs of borax ingestion in animals include excessive drooling, vomiting (sometimes with a blue-green color), diarrhea, loss of appetite, and lethargy. Young animals and very old animals tend to be more sensitive than healthy adults.
Practical precautions make a big difference. Place bait stations inside enclosed containers with small entry holes that ants can access but toddlers and pets cannot. Tape containers to walls behind furniture, set them under heavy appliances, or place them inside cabinets where you’ve seen ant trails. The liquid bait recipe above uses a very low borax concentration, but you still don’t want a curious dog drinking from an open cup. Label your bait stations clearly so other household members know what they are.
Why Borax Bait Sometimes Fails
The most common reason borax bait doesn’t work is using too much borax. If ants taste the bait, take a few sips, and die on the counter, the concentration is too high. Scale it back. You want ants happily marching between the bait and their nest for days.
The second most common problem is offering the wrong food. If ants walk past your sugar bait without interest, they’re likely seeking protein or fat. Try peanut butter, or even a greasy bait made with shortening and borax.
Bait placement matters too. Set stations directly on active ant trails, not just in the general area where you’ve seen ants. If you can trace the trail to where ants enter the house (a crack in the baseboard, a gap around a pipe), place a station right there. Multiple stations along the same trail increase uptake.
Finally, don’t clean up the ant trail with soap or spray while you’re baiting. Ants follow pheromone trails, and wiping those trails away forces surviving ants to find new routes, potentially bypassing your bait stations entirely. Let the trail stay active until the colony collapses.