Boric Acid Ant Killer: How It Works, How to Use It and What Canadians Should Know

TL;DR

• Boric acid kills ants as a slow-acting bait: workers eat it and share it with the colony, so it reaches the ants you never see.
• In Canada, use only sealed bait stations or gels with a PCP number on the label. Home-use dusts and most liquids were cancelled (Health Canada).
• Don't mix your own boric acid and sugar bait. You cannot control its strength, and more boric acid is not better (Health Canada).
• Place stations right on the ant trails, out of reach of children and pets, and stop all sprays while you bait. Spraying stops the bait system from working (Health Canada).
• Keep baits out for at least two weeks, as Health Canada advises, and don't crush the ants on them. It can take 5 to 10 days to see fewer ants.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

The usual reason a boric acid ant killer fails is that it works too fast: a strong homemade mix kills foragers right at the bait, and the colony behind the wall never feels it. Used the right way, boric acid does wipe out ants, but only as a weak, slow bait that workers carry home.

That changes what you should buy. Health Canada advises against homemade boric acid pesticides, and only sealed bait stations and gels are still allowed for home use, so the real choice is where to place a registered bait and how long to leave it alone.

Patience is the hard part, since a pile of dead ants at the bait looks like success. What decides the outcome is how the poison moves from one ant to the next inside the nest.

What Is Boric Acid and How Does It Kill Ants?

A boric acid ant killer is a slow-acting stomach poison that ants eat in a bait and share with the rest of the colony (NPIC describes boric acid as a stomach poison). The ants come for the sugar or grease in the bait, not for the boric acid. A dose taken by one forager today can reach ants deep inside the nest over the following days, since worker ants feed each other and their larvae. That is the whole point of boric acid: it kills the ants you never see.

What Is Boric Acid?

Boric acid is a pesticide made from boron, a substance that occurs naturally in soil, water and plants, according to the National Pesticide Information Center (NPIC) at Oregon State University. Products containing boric acid have been registered as pesticides in the United States since 1948. It is sold in several forms, including baits, dusts, granules and liquids, but Canada now allows only some of them for home use.

How Boric Acid Kills Ants

Boric acid kills ants once they swallow it. NPIC explains that it disrupts an insect's stomach and can affect its nervous system, and that it can also scratch and damage the outside of the insect's body. When ants walk through boric acid dust, it sticks to their legs and they swallow it while grooming, Orkin notes. In a bait, though, ants simply drink or eat it along with the food.

Why Slow Action Matters

Slow action is what lets boric acid reach the queen. Health Canada explains that a bait system must work slowly enough for the poison to be fed to all members of the nest, and UC IPM (University of California) adds that the pesticide must act slowly so workers are not killed before they get back. Researchers at UC Riverside cite a study showing that a single worker feeds many other workers. If the bait kills the forager on the spot, that chain never starts, and the colony just replaces the workers it lost.

Boric Acid vs Borax

Boric acid and borax are close chemical cousins that kill ants the same way, through the boron they contain. According to UC Riverside researchers, their toxicity to ants depends only on their boron content: boric acid is 17.5% boron by weight, and anhydrous borax is 21.5%. Health Canada regulates them together. Most borate ant baits sold in Canadian stores use borax rather than boric acid, so if that is what you have, read our guide to using borax to kill ants.

Can You Use Boric Acid for Ants in Canada?

Boric acid for ants is still allowed in Canada, but only inside sealed bait stations and localized gels. This matters because many older articles and online recipes still tell you to sprinkle boric acid powder or squirt a boric acid liquid along your baseboards. In Canada, those products were taken off the market for home use.

What Health Canada Cancelled

Health Canada's re-evaluation of boron pesticides (decision RVD2016-01, published July 22, 2016) covered boric acid, borax and related compounds. For home use, dust and granular products, and liquid products other than sealed bait stations or localized gels, were cancelled. Their sale was prohibited as of July 22, 2018, and their use had to stop by July 22, 2019. At the time, 112 registered products contained boric acid, and 25 of them were cancelled. Health Canada's list of cancelled home products includes some liquid ant killers.

What Is Still Allowed

Sealed bait stations and localized gel treatments are still allowed, as they can expose people to much less boron than loose powder or open liquid; Health Canada notes such baits are generally of low toxicity to other animals. Health Canada requires their labels to say "Apply/use only in areas inaccessible to children and pets." The other registered products stayed on the market with stronger label directions.

The PCP Number

The PCP number is your proof that a boric acid ant killer is registered in Canada. Health Canada advises you to always look for a Pest Control Products (PCP) number on the label, and to follow every direction on it. A jar of boric acid sold for other uses has no PCP number and no ant directions, so it is not an ant killer in the eyes of the law.

Old Boric Acid Products

Old boric acid powders and liquids you may still have in the garage should not be used. Health Canada advises Canadians not to use cancelled boric acid pesticides once their registration has expired, and says to contact your provincial or territorial government to find out how to dispose of them safely. Do not pour them down the drain or into the garden.

How Do You Use a Boric Acid Ant Bait?

A boric acid ant bait usually works when the ants can feed on it, undisturbed, for at least two weeks (Health Canada). Follow these steps with a registered bait station or gel:

1. Identify the ant.
2. Remove competing food.
3. Place baits on the ant trails.
4. Stop spraying.
5. Check and replace the baits.
6. Wait for the colony to die out.

Identify the Ant

Identifying the ant tells you which bait it will eat. Health Canada lists the carpenter ant, little black ant, odorous house ant, thief ant and pharaoh ant among the species that invade homes in Canada, and pavement ants also come indoors. UC IPM notes that thief and pharaoh ants prefer protein or greasy baits all year, while some other ants go for sweets. Tiny ants on the sugar bowl call for a sweet bait, as our guide to getting rid of sugar ants explains. Tiny pale ants spreading from room to room may be pharaoh ants, which need a different approach.

Remove Competing Food

Removing competing food makes the bait the best meal in the house. Health Canada advises storing ant-attractive foods in glass jars with rubber gaskets or in plastic containers with snap-tight lids, keeping counters clean and emptying kitchen garbage often. Wipe up sweet spills and crumbs before you set out the bait.

Bait Placement

Bait placement decides whether the boric acid reaches the colony. Health Canada advises placing bait stations directly in the path of foraging ants, out of the reach of children and pets. It also recommends using plenty of stations, and says two different baits at the same time give better results. Look for trails along baseboards, counter edges and cabinet corners, and put a station wherever you see ants coming inside.

Stop Spraying

Stopping all sprays lets the bait do its work. Health Canada warns that if you spray chemicals to kill ants while using a bait system, the bait system will not work, and UC IPM gives the same advice. The City of Calgary adds that some chemical barrier sprays may cause a colony to split into new nests. Leave the trail alone too: do not wipe it with vinegar or cleaners while you bait.

Check and Replace Baits

Checking the baits regularly keeps the ants feeding. UC IPM notes that baits can dry up or turn rancid over time, so replace a station once it is empty or spoiled. If the ants ignore a bait, move it closer to the trail or try a different product. Health Canada says to keep baits available for at least two weeks, and repeat the treatment if needed.

How Long Boric Acid Takes to Kill Ants

A boric acid ant killer takes days to weeks, not hours. You may see a crowd of ants on the bait at first, which is a good sign: they are carrying it home. UC IPM says it can take 5 to 10 days to see fewer ants, and complete control can take several weeks or more. Do not crush the ants on the bait, since they are the ones delivering it to the nest.

Does a Boric Acid and Sugar Ant Killer Work?

A boric acid and sugar ant killer can work, but only in a narrow strength range that kitchen recipes rarely hit. The sugar makes ants drink it, and the boric acid has to be weak enough that they live long enough to share it.

Why Strength Matters

Strength decides whether the bait reaches the queen. UC Riverside researchers found that baits with 5% or more borates affect ants too quickly, which stops them from recruiting nestmates and spreading the poison, and there are reports of ants dying right at the bait station. In their tests, a bait with 6.25% boric acid was barely eaten. Their best results came from much weaker mixes, and UC IPM says effective borate baits are 1/2 to 1% boric acid and 10 to 25% sucrose in water. UC IPM also notes that prepackaged stations, which usually hold 5.4% borate, kill foragers but are less effective against large infestations than liquid baits of 0.5 to 1.0% borate in sugar water. More boric acid is not better.

Why Health Canada Advises Against Homemade Bait

Health Canada advises against making homemade pesticides with boric acid, and reminds Canadians never to make homemade pesticides using boric acid or boron. Its concern is overexposure, which has the potential to cause developmental and reproductive health effects, especially when boron comes from many sources at once, and NPIC notes such effects in studies with mice. A homemade boric acid and sugar syrup has three problems: you cannot control its strength, it usually sits in an open lid or jar that children and pets can reach, and it can dry out quickly, a Canadian review site found (UC IPM notes some products dry up rapidly), so it needs constant refilling. The old recipes passed around online often use far more boric acid than the 0.5 to 1% that UC IPM says is more effective.

A Safer Alternative to Homemade Bait

A registered borate bait station or gel is the safer alternative to homemade bait. It holds a measured dose inside a closed container and comes with tested directions. For example, Terro Liquid Ant Baits contain 5.40% borax, and Green Way Liquid Ant Bait, registered in Canada, uses a related boron compound at 1% and tells you to keep enough bait out for at least 14 days of feeding, as Health Canada also advises. To compare ready-made options, see the best ant killer roundup.

Is Boric Acid Safe Around Children and Pets?

Boric acid is low in acute toxicity, NPIC notes, but it is not harmless, and children and pets are the ones most at risk. Health Canada says baits containing boric acid are generally of low toxicity to other animals when used as directed, which is why the label matters.

Health Effects in People

Boric acid is low in toxicity if eaten or if it touches the skin, according to NPIC, but people who swallowed it have had nausea, vomiting, stomach aches and diarrhea. Borax can be corrosive to the eyes. UC Riverside researchers, citing the US Environmental Protection Agency, note that borates may be more toxic to children than to adults, and NPIC notes that children have behaviours that can put them at greater risk. Health Canada's main worry is repeated overexposure from many products at once.

Boric Acid and Pets

Pets react to boric acid much like people do, and NPIC says signs of poisoning can start within 2 hours of eating it. Put stations behind appliances, under cabinets or inside cupboards your pets cannot open, and never leave open dishes of bait on the floor. For other options, read our guide to pet-safe ant killers.

Safe Storage

Safe storage means keeping unused baits in their original package, with the label, away from food and out of reach of children and pets. Never move boric acid into a food or drink container, and wash your hands after placing or removing stations.

If Someone Swallows Bait

If a child or pet gets into a boric acid bait, call your doctor, a poison control centre or your veterinarian right away, and have the product label in hand. Do not try to treat it at home.

How Does Boric Acid Compare With Other Ant Killers?

Boric acid compares well with other ant killers because it reaches the colony, while most alternatives only kill or chase away the ants you see. Still, it is not the right tool for every ant or every home.

Diatomaceous Earth

Diatomaceous earth is a non-chemical option. Health Canada describes it as a powder made of crushed microscopic marine fossils that is non-toxic to humans and pets, though you should not breathe in the dust, and it stays active only while dry. It kills ants that crawl through it but does not travel back to the nest the way a bait does. To see how it stacks up against a borate bait, read diatomaceous earth vs borax.

Repellents

Repellents such as vinegar and peppermint oil push ants away from a spot rather than killing the colony. Vinegar mainly disrupts the scent trail for a while, and UF/IFAS warns that repellent products can make some ant colonies, such as pharaoh ants, split into new nests. Never use them on the same trail as a boric acid bait. To see what home remedies can and cannot do, read does vinegar kill ants, our guide to cornmeal as an ant killer and our roundup of homemade ant killers.

When to Call a Pest Control Professional

Calling a licensed pest control professional makes sense when ants keep coming back after several weeks of baiting, when ants show up in many rooms at once, or when you suspect carpenter ants. Orkin notes there is no guarantee that over-the-counter boric acid products will kill a whole colony, and UC IPM says boric acid concentrations higher than 1%, as in some commercial products, are less effective; carpenter ants that nest in wood are a structural problem, covered in our guide on how to get rid of carpenter ants. When you are ready, you can get a quote from a recommended local exterminator through Pest Agent's referral form.