Mixing borax with peanut butter creates a slow-acting poison that worker ants carry back to their nest, eventually killing the queen and collapsing the colony. The key ratio is half a teaspoon of borax to two tablespoons of creamy peanut butter, keeping the borax concentration between 1% and 5% of the total mixture. Too much borax kills foragers before they make it home; too little won’t eliminate the colony.
Why This Combination Works
Borax acts as a stomach poison. Ants can’t detect it in small amounts, so when it’s mixed into something appealing like peanut butter, they treat it as a normal food source. Workers collect the bait and bring it back to the nest, where they feed other workers, larvae, and the queen through mouth-to-mouth food sharing (a behavior called trophallaxis). This turns every forager into an unknowing delivery system, spreading the poison deep into the colony where sprays and surface treatments can’t reach.
The slow-acting nature of borax is the whole point. A fast-killing poison would drop ants at the bait station, and the colony would learn to avoid it. Borax takes long enough to work that dozens or hundreds of ants feed on the bait and distribute it before any symptoms appear.
The Right Recipe and Ratio
The standard protein bait recipe is simple:
- 1/2 teaspoon borax (sodium tetraborate, sold as 20 Mule Team Borax in the laundry aisle)
- 2 tablespoons creamy peanut butter
Mix them thoroughly until the borax is completely incorporated. You want no visible white powder, just a uniform paste. Creamy peanut butter works better than chunky because it blends more evenly and is easier for ants to carry in small pieces.
If ants seem to be dying too quickly near the bait (you see dead ants piling up around it), you’ve used too much borax. Scale it back. The goal is a concentration low enough that ants survive for days after feeding, giving them time to share the bait throughout the colony.
Which Ants Peanut Butter Actually Attracts
Not all ants want peanut butter. Ant colonies shift their dietary needs depending on what the colony is doing at any given time. When they’re building nests and foraging heavily, they crave sugars for energy. When they’re producing eggs and raising larvae, they seek out protein and fat. Peanut butter is a protein and grease bait, so it works best when the colony is in a growth phase.
Research from Texas A&M found that most ant species collected in field traps actually preferred carbohydrate baits over protein ones. Fire ants showed up at both types, but ghost ants ignored protein traps entirely. Arboreal species (ants that nest in trees and walls) tended to prefer protein, while ground-dwelling species leaned toward carbohydrates. If you’re dealing with tiny sugar ants trailing through your kitchen, peanut butter alone may not be enough to get their attention.
What to Do if Ants Ignore the Bait
If ants walk right past your peanut butter bait, the most likely explanation is that the colony doesn’t need protein right now. Switch to a sugar-based bait instead: dissolve half a teaspoon of borax in one cup of warm water with two tablespoons of sugar, then soak cotton balls in the solution and place them along ant trails. You can also set out both types simultaneously and let the ants choose.
Another common reason for bait rejection is placement. Ants following an established chemical trail to another food source will march right past your bait because they’re locked onto that trail’s scent. Given time, a scout ant will discover the bait and lay a new trail to it, but this can take hours or even a day. Don’t move the bait around impatiently.
One overlooked detail: if you place bait on a jar lid or container that was washed with dish soap, residual detergent can repel ants. Rinse any container thoroughly with plain water before using it as a bait station.
How to Set Up Bait Stations
Spread small amounts of the peanut butter mixture (about a pea-sized blob) onto pieces of cardboard, bottle caps, or cut sections of rigid plastic. Place them directly along ant trails, near entry points where ants come into your home, and close to any visible nest openings outside. The goal is to intercept ants where they’re already traveling, not to lure them across the room.
Use multiple small stations rather than one large one. Ants recruit nestmates to nearby food sources, so several stations along a trail will get more foragers feeding faster. Replace the bait every two to three days, since peanut butter dries out and becomes less attractive.
Timeline for Colony Elimination
Don’t expect overnight results. The first week or two, you may actually see more ants as word spreads through the colony that there’s a new food source. This is a good sign. It means the bait is being collected and shared.
Smaller colonies typically show significant decline within one to two weeks. Larger infestations, particularly Argentine ant colonies that can span enormous networks, may need three to four weeks of consistent baiting. Keep refreshing bait stations as long as you see ant activity. Stopping too early lets the queen and surviving workers rebuild.
Keeping Pets and Children Safe
Borax is relatively low in toxicity compared to many pesticides, but it’s not harmless. Dogs appear to be more sensitive to it than rodents in lab studies. Small amounts ingested by pets can cause excessive drooling, vomiting, diarrhea, fever, and loss of appetite, with symptoms typically appearing within two hours. Vomit or stool may have a blue-green color. Young and older animals tend to be more sensitive than healthy adults.
The amount of borax in a single bait station is very small (half a teaspoon spread across multiple stations), so a dog licking one station is unlikely to cause serious harm. The real risk comes if a pet eats multiple stations or gets into the borax box itself. To minimize risk, place bait stations in spots pets and toddlers can’t access: inside cabinets, behind the stove, under the refrigerator, or inside a sealed container with small holes punched in it (big enough for ants, too small for a dog’s tongue). A plastic food container with a few quarter-inch holes drilled near the base makes an effective pet-proof bait station.
For homes with very young children who crawl and put everything in their mouths, stick to enclosed bait stations placed at ground level behind furniture or appliances, and avoid open bait on cardboard in any area a child can reach.