Cornmeal Ant Killer: Does It Work, and What to Use Instead

TL;DR

• No, cornmeal does not kill ants. Ants that eat it are fed, not poisoned.
• The swelling story is a myth. Adult ants filter out most solid particles and live mainly on liquids, so dry cornmeal does not sit in their gut waiting to expand.
• Already spread some? Sweep or vacuum it up so it stops acting as a food source. In one published case, the ants carried it back to the nest and a minor ant problem turned into a major one.
• Skip the homemade cornmeal and boric acid recipe. Don't make homemade pesticides with boric acid (Health Canada).
• Use a registered, slow-acting bait instead. As Health Canada advises, look for a PCP number on the label and place stations right in the path of foraging ants, out of reach of children and pets.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

A cornmeal ant killer sounds like the perfect pantry fix, cheap and harmless around kids and pets, but it does not kill ants. Plain cornmeal hands a colony a free meal, and the swelling story that keeps the idea alive does not match the way ants feed.

The myth sticks because it borrows from something real. Corn grit is a common ingredient in genuine ant baits, where it carries an insecticide that workers bring home to the nest, and people who watched those baits work gave the credit to the corn.

Does Cornmeal Kill Ants?

Cornmeal does not kill ants: ants that eat it are fed, not poisoned. Cornmeal is simply dried corn ground into a coarse, medium or fine meal, with nothing in it that is toxic to insects. Garden writers, newspaper columnists and pest control companies who have looked at the claim all reach the same conclusion: spreading plain cornmeal around your home gives ants a free meal.

Where the Cornmeal Myth Comes From

The cornmeal myth comes from a story that sounds logical: ants eat dry cornmeal, drink water, the meal swells inside them and they die. Some versions blame gas, and others swear by grits instead of cornmeal. Garden writer Larry Hodgson (the Laidback Gardener) called the legend nonsense and pointed to a likely origin: many commercial ant baits are mostly corn, which ants love. People saw corn-based bait killing ants and assumed the corn was doing the work, when the insecticide mixed into it was.

Why Cornmeal Cannot Kill Ants

Cornmeal cannot kill ants because adult ants never swallow it as a solid. Worker ants forage for solid food but do not eat it themselves. In his book Fire Ants, Stephen Welton Taber explains that adult ants have a filter near the mouth that screens out solid particles, so they live on liquids. Workers usually carry solid food back to the nest, where the larvae digest it and pass a liquid back to the workers, who share it with the queen. At no point does a lump of dry cornmeal sit in an adult ant's gut waiting to expand.

What Happens When You Use Cornmeal for Ants

Using cornmeal for ants usually means feeding the colony. In one case published by a US pest control company, a homeowner spread large piles of cornmeal around his house after reading that it would kill ants. The ants reportedly carried it back to the nest, and a minor ant problem turned into a major one. If you have already sprinkled cornmeal, sweep or vacuum it up so it stops acting as a food source.

How Is Cornmeal Used in Real Ant Baits?

Cornmeal, in the form of defatted corn grit, is used in real ant baits, but only as the carrier for an insecticide. This is the grain of truth behind the myth. Many granular ant baits, especially those made for fire ants, are built from three parts.

Corn Grit Carrier

Corn grit is the carrier in many granular ant baits. Texas A&M AgriLife Extension describes ant bait products as a carrier, usually defatted, processed corn grit, plus an attractant in which the active ingredient is dissolved. Its fire ant bait guide is clear that although ants carry the corn granules back to the mound, the granules have no insecticidal properties. The corn is just the delivery vehicle.

Soybean Oil Attractant

Soybean oil is the attractant that makes the bait appealing, and it also holds the active ingredient. Texas A&M notes that fresh bait smells like toasted corn, while old bait goes rancid, smells somewhat like latex paint and stops attracting ants. Bait left open to the air can turn rancid over time (UC IPM), and water ruins bait particles, so the Texas A&M guide advises against applying bait if rain is expected within 24 hours.

Active Ingredient

The active ingredient is the only part of a corn-based bait that kills ants. It has to be slow-acting: UC IPM explains that the pesticide must work slowly so workers are not killed before they get back to the nest. There, the bait is passed mouth to mouth to other workers, larvae and queens, which is how a bait reaches the whole colony. Without an active ingredient, a corn bait is just food.

Should You Make a Cornmeal and Boric Acid Ant Killer?

A cornmeal and boric acid ant killer is not recommended in Canada: Health Canada advises against making homemade pesticides with boric acid. This recipe is what many websites, including the earlier version of this page, call a cornmeal ant killer, so it deserves a clear answer.

The Classic Homemade Recipe

The classic homemade recipe mixes cornmeal with boric acid or borax and enough soybean oil to make a paste, then sets it out in a small container with holes for the ants. In theory, it copies the carrier, attractant and active ingredient of a commercial bait. In practice, the strength of the mix is guesswork. Too much boric acid can kill workers before they reach the nest, too little may do nothing, and Health Canada notes that homemade pesticide recipes are not scientifically tested for their effects on health and the environment, unlike products the US EPA reviews before sale.

Health Canada Advice on Boric Acid

Health Canada's advice on boric acid is direct: do not make homemade pesticides using boric acid. Some uses of boric acid can cause overexposure, and children are among those most at risk; Health Canada says to keep baits out of reach of children and pets. Canada has also cancelled and phased out certain boric acid pest control products. Instead, Health Canada recommends using only registered pesticides with a Pest Control Products (PCP) registration number on the label. Registered boric acid and borax baits still exist; to learn how they work, read our guides to boric acid ant killer and using borax to kill ants.

Pets and Children

Pets and children are the main reason to skip an open homemade bait. Health Canada recommends placing pesticides only where children and pets cannot reach them, such as behind appliances, in cracks and crevices, or in enclosed bait stations, and NC State Extension gives the same advice for ant baits. A yogurt cup full of sweetened paste on the kitchen floor does not meet that standard. If you share your home with a dog or cat, our guide to pet-safe ant killers covers safer choices.

How Do You Get Rid of Ants Without Cornmeal?

Getting rid of ants without cornmeal works best with a registered, slow-acting bait that worker ants carry back to the nest. This is the method recommended by Health Canada and UC IPM, and it targets the queens you never see.

Registered Bait Stations

Registered bait stations are the safest way to get the corn-bait effect without guesswork. Look for a PCP number on the label and check that your type of ant is listed, as Health Canada advises. For example, UC IPM notes that prepackaged borate stations usually contain 5.4% borate. Labels matter here: TERRO states that its liquid borax baits are not effective on carpenter, pharaoh or fire ants. For tested picks available in Canada, see our best ant killer roundup.

Bait Type

Bait type should match what your ants are eating right now. Health Canada notes that ants enjoy sugary and greasy foods, and UC IPM points out that some species, such as thief ants and pharaoh ants, prefer protein or greasy baits all year. UC IPM suggests offering small amounts of different baits and watching which one the ants take. If they ignore a station, try another type.

Bait Placement

Bait placement decides whether the colony ever gets the bait. Health Canada advises placing bait stations directly in the path of foraging ants, out of reach of children and pets. While baiting, do not spray insecticides or wipe the trail: Health Canada and TERRO both warn that spraying while a bait system is in use reduces its effect.

How Long Baits Take

Baits take time because they work through the colony. UC IPM says it can take 5 to 10 days to see fewer ants, and full control may take longer. Health Canada recommends keeping baits out for at least two weeks. Do not panic if you see more ants in the first days: TERRO notes that ant numbers often rise at first as foragers find the bait, then drop.

Food Storage

Food storage keeps ants focused on the bait and helps prevent the next invasion. Health Canada says removing access to food and water is the easiest way to avoid pest problems. Store food in sealed containers, keep counters clean, empty the garbage often, and set your pet's food dish in a shallow dish of water, since ants cannot swim across it. For a full room-by-room plan, read our guide on how to get rid of ants.

When to Call a Pest Control Professional

Calling a pest control professional makes sense when baits fail after several weeks, when ants keep coming back from inside the walls, or when you see large black ants that could be carpenter ants, a species that can cause structural damage. A licensed professional can identify the species and choose a treatment that fits it. You can get a quote from a recommended local exterminator through Pest Agent's referral form, and our ant hub covers each common Canadian species.

What Natural Alternatives to Cornmeal Work on Ants?

Natural alternatives to cornmeal can reduce ants, but most only kill on contact or repel them, so they work best alongside a bait. Here is what each one really does.

Diatomaceous Earth

Diatomaceous earth is the natural option with the clearest mechanism. According to the National Pesticide Information Center, it makes insects dry out and die by absorbing the oils and fats from their outer shell, and Health Canada notes it stays active only as long as it is kept dry. Health Canada lists it as a non-chemical option that is non-toxic to humans and pets, but warns not to breathe in the dust when applying it. Learn how to apply it in our guide to diatomaceous earth for ants.

Vinegar

Vinegar wipes away ant trails but does not reach the nest. UC IPM notes that simply washing a trail with soapy water removes the scent ants follow, and that killing foragers does not kill the colony or the queens. Vinegar works the same way: useful for cleaning, not a colony killer. See does vinegar kill ants for details.

Cinnamon

Cinnamon is a popular kitchen remedy for ants, but no Health Canada or university extension source we checked shows that it eliminates a colony. At best, it may discourage ants from crossing a line. Our guide on cinnamon for ants explains how people use it.

Boiling Water

Boiling water works only on nests you can reach outdoors. Health Canada says pouring boiling water and detergent down a nest temporarily reduces the colony's population. Keep it away from lawns and plants you want to keep, and never use it indoors.

Homemade Ant Killers

Homemade ant killers range from sugar and baking soda mixes to soap sprays, and their results vary widely. If you want to try one, our guides to homemade ant killers and whether baking soda kills ants compare the common recipes and their limits.