How to Get Rid of Ant Hills in Your Lawn and Yard for Good

TL;DR

• It takes two steps: flatten the mound, then kill the colony underneath with slow-acting bait.
• Rake the mound flat or wash it out with a strong stream from the garden hose. On its own, this usually does not kill the colony.
• Put bait stations or bait stakes near the mound and along the ant trails, as UC IPM advises, out of reach of children and pets. Don't spray or rake nearby while the ants feed.
• Skip boiling water on the lawn. It often fails to kill the whole colony, and it can kill grass and plants.
• Thick grass can help keep new hills away: water regularly and mow at three to four inches (about 7.5 to 10 cm).
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

Working out how to get rid of ant hills usually starts with a mound you raked flat on the weekend and found rebuilt in the same spot a day or two later. Boiling water and sprays give the same short win: the ants on top die, the grass around the hill often dies with them, and the colony carries on.

The hill keeps returning for a simple reason. Whatever you do to the surface usually leaves the egg-laying queen, and most of the colony with her, out of reach underground.

What Are Ant Hills?

Ant hills are piles of soil that ground-nesting ants carry up from their underground nest, so each hill marks the entrance to a colony living below. Health Canada describes anthills as the place where the colony has built its nest, which makes them the easiest way to find a nest in your yard. Most of what matters is out of sight: the hill is the doorstep, not the house.

What Is Under an Ant Hill?

Under an ant hill is typically a network of underground tunnels where the colony lives (City of Calgary). The ants you see on the surface are only a small part of it. According to the University of Kentucky Cooperative Extension, many more ants, including one or more egg-laying queens, stay hidden in the nest. That is why kicking or raking a hill flat makes it disappear for a day or two, then it comes back: the queen is still laying eggs below.

Why Do Ant Hills Appear After Rain?

Ant hills appear after rain because wet soil pushes the colony to move higher. Texas A&M AgriLife explains that when the ground is saturated, ants may move their colonies up, so mounds that were always there can suddenly become visible. Iowa State University Extension adds that ant nesting activity tends to peak in wet spring weather, which is often when Canadian lawns start showing new hills.

Are Ant Hills Bad for Your Lawn?

Ant hills in a lawn are mostly a cosmetic problem. North Dakota State University (NDSU) Extension notes that the small ants behind many lawn mounds rarely cause actual injury to the grass itself. Large mounds can smother the grass underneath and can dull mower blades, according to UMass Extension. Ants also do useful work: Health Canada and the City of Calgary point out that they eat other insects and cause little damage in the garden.

In vegetable beds, the story is a little different. Iowa State notes that ants generally do not eat roots, but their digging can leave roots exposed to the air so they dry out. For ants in flower and vegetable beds, see our guide to plant-safe ant killers for the garden.

Do Ants in Ant Hills Bite or Sting?

Most ants in ant hills rarely bite or sting unless handled carelessly, according to Iowa State, and UC IPM says most species rarely bite. There are two exceptions in Canada, covered below, and UC IPM notes that a few ants sting: Allegheny mound ants bite when their mound is disturbed, and European fire ants sting, even though they do not build visible hills.

Which Ants Build Ant Hills in Canada?

Ant hills in Canadian lawns are built mostly by pavement ants and small brown lawn ants, and knowing which one you have changes how you treat it. Canada has over 100 species of ants (City of Calgary), but only a handful nest in lawns and leave mounds behind.

Pavement Ants

Pavement ants are the ant hill builders you see along sidewalks, driveways and foundations. Health Canada lists them as a nuisance in lawns, gardens and pathways, as well as indoors. According to UC IPM, workers are about the same size and dark brown to black, they nest in lawns or under stones and boards, and they often build mounds in clusters along sidewalks and near foundations. They eat sweets, greasy foods, insects and pet food, which is why they take baits well.

Lawn Ants

Lawn ants (the genus Lasius, also called turfgrass ants or cornfield ants) often make small, crater-shaped mounds that are easy to spot. NDSU Extension says they often nest along gravel driveways, in cracks in cement walkways, between patio paver stones and in lawns where the soil is exposed. The University of Maine describes the cornfield ant as a small, light to dark brown ant that piles its soil around the rim of the nest opening, and calls it one of the most common ants in New England lawns. They feed on dead insects and on honeydew from aphids.

Allegheny Mound Ants

Allegheny mound ants build some of the largest ant hills you are likely to see in eastern Canada. Their range reportedly extends from Nova Scotia south into the United States, and older mounds can reach about 1 m tall and 2 m across. These ants can kill the plants growing on and around their mound by injecting formic acid into the stems, and they bite when the mound is disturbed. A mound this size near a play area is a good reason to get professional help.

European Fire Ants

European fire ants are a stinging lawn ant that usually does not build above-ground ant hills. The Invasive Species Council of BC says these red-brown ants, about 2 to 3 mm long, arrived in BC around 2010 and may quickly take over lawns, parks and golf courses. With no hills to give them away, they usually turn up when they swarm and sting after you disturb the soil. The council advises not to try to remove a nest yourself and not to move soil, turf or leaf litter off your property: contact your local government or regional invasive species organization instead. Our guide to getting rid of fire ants covers them in more detail.

How Do You Get Rid of Ant Hills?

Getting rid of ant hills takes two steps: flatten the mound, then kill the colony underneath with slow-acting bait. Flattening fixes how the lawn looks, and baiting fixes why the hill keeps coming back. The methods below are listed from the simplest to the last resort.

Flattening the Ant Hill

Flattening the ant hill is the first and safest step. Iowa State University Extension suggests raking mounds flat as needed, or washing them out with a forceful stream of water from the garden hose to spread the soil. Repeat it often during wet spring weather, when ants rebuild fastest. On its own, flattening usually does not kill the colony, but on a lawn where the ants cause no real harm, it may be all you need.

Outdoor Ant Bait

Outdoor ant bait is the most effective way to get rid of an ant hill for good. NDSU Extension calls outdoor baits the best option for lawn ants, and UC IPM calls baits a key tool: worker ants bring the bait back to feed the colony, which can poison the entire nest, including the queen. Here is how to use it:

1. Place bait stations or bait stakes right beside the mound and along the ant trails leading to it, out of reach of children and pets.
2. Leave the area alone: do not spray insecticides nearby, and do not rake the mound while the ants are feeding.
3. Expect more ants around the bait at first. The University of Kentucky calls this a good sign, and UC IPM notes that slow-acting baits let foraging ants make their way back to the nest.
4. Give it time. UC IPM says it can take 5 to 10 days to see fewer ants, and NDSU says up to a week.
5. Replace empty baits. If the ants ignore a bait, move it or try a different type, since UC IPM recommends offering different bait formulations to give ants a choice.

Boiling Water

Boiling water kills the ants it touches but often fails to kill the whole colony. Health Canada says pouring boiling water and detergent down the nest temporarily reduces the population. For fire ant mounds, Oklahoma State University Extension found that about 3 gallons (about 11 litres) of boiling water per mound eliminated only some of the mounds treated, so the rest had to be treated again. It also warns that carrying that much boiling water is hazardous, and that it must not be poured on grass or other plants. If you use it, keep it for hills in cracks in the pavement or between patio stones, wear closed shoes, and pour slowly.

Flooding the Nest

Flooding the nest with a garden hose pushes ants to move rather than killing them. Health Canada suggests flooding ant nests repeatedly to encourage the colony to move farther from your house. This works well for a hill against the foundation or beside the back steps, where you would rather have the ants out in the yard.

Diatomaceous Earth

Diatomaceous earth is a non-chemical powder that dries out the ants that crawl through it. Health Canada says it stays active only while it is dry and is non-toxic to people and pets, but you should avoid breathing in the dust. It usually kills only ants that touch it and, according to Health Canada, works only while it is kept dry, so it is better around cracks and near hills than as a cure for a big colony on an open lawn. Our guide to using diatomaceous earth for ants explains how to apply it.

Vinegar

Vinegar usually disrupts ant trails for only a short time and does not kill the colony under an ant hill. It will not reach the queen, so the hill tends to come back. See our test of whether vinegar kills ants for the details.

Protecting Your Grass

Protecting your grass means choosing methods that stay on the mound and away from the turf. Skip boiling water on the lawn itself, since Oklahoma State warns it kills grass and plants, and Texas A&M AgriLife notes it may kill nearby roots. Bait is the grass-friendly option, because the ants carry it underground and nothing is sprayed on the turf. Once the colony is gone, rake the old mound level and reseed any bare spot so new ants have no open soil to move into.

Multiple Ant Hills

Multiple ant hills across the lawn usually mean several colonies, not one. Bait each area where you see active mounds instead of one spot in the middle of the yard. If dozens of small lawn ant hills cover a large lawn and the ants are not stinging or coming indoors, raking and better lawn care are often more practical than treating every mound.

When to Call a Pest Control Professional

Calling a licensed pest control professional makes sense if you suspect European fire ants, if a large Allegheny mound sits near where children play, or if hills next to the house keep coming back after weeks of baiting. UC IPM suggests asking any company you hire to use baits and spot treatments rather than perimeter treatments or monthly sprays. You can get a quote from a recommended local exterminator through Pest Agent's referral form. For ants all around the outside of the house, not just in mounds, read how to get rid of ants outside.

What Is the Best Ant Hill Killer?

The best ant hill killer for most Canadian lawns is usually a slow-acting outdoor ant bait, because, as UC IPM notes, workers get back to the nest before they are killed, and a spray on the mound rarely touches the queen. Contact insecticides come second, as a last resort for a stubborn mound. For tested products, see our picks for the best ant killer.

Bait Stakes

Bait stakes are small stations filled with liquid bait that you push into the soil next to an ant hill. Many outdoor liquid baits use borax (a boric acid compound) as the slow-acting ingredient, which NDSU describes as a stomach poison, and UC IPM notes that ants take baits back to the nest, where the entire colony can be killed. Check the label for the ants it targets: borax liquid baits are made for sweet-eating ants such as pavement and lawn ants, and some are not labelled for fire ants or carpenter ants.

Granular Ant Bait

Granular ant bait is scattered around the mound and along trails, where foragers pick up the granules and carry them in. Do not water granular bait in: NDSU warns that water breaks the bait down faster.

Insecticide Mound Treatments

Insecticide mound treatments (granules scattered or dissolved and poured into the nest, or foams sprayed into the hill) kill ants on contact, but they often miss the queen deep below. Iowa State and NDSU both describe them as a last resort for lawns. NDSU warns that broad-spectrum lawn insecticides can also harm ground-nesting bees and other beneficial insects, a risk OMAFRA in Ontario also notes, and UC IPM advises against spraying pyrethroids on hard surfaces or around foundations because they wash into waterways. If you use one, treat only the mound, never the whole lawn, and follow the label exactly. The City of Calgary also notes that some barrier sprays can make a colony split into new nests; if that happens, switch to bait.

The PCP Number

The PCP number is the proof that a product is registered for use in Canada. Health Canada says to always look for a Pest Control Products (PCP) number on the label and to follow every direction on it. Also check that the label says outdoor use and lists the kind of ant you have.

Provincial Pesticide Rules

Provincial pesticide rules can limit which ant hill killers you may use on a lawn. Ontario bans the cosmetic use of pesticides on lawns and gardens, as OMAFRA notes, and generally allows only low-risk products from its Allowable List, unless an exception applies. Health Canada notes that some provinces and municipalities restrict certain lawn and garden pesticides, so check with your city, your province or a local garden centre before you buy.

Pet and Child Safety

Pet and child safety comes first with any ant hill killer. Place baits where children and pets cannot reach them (City of Calgary). Health Canada allows domestic boric acid products only as sealed bait stations or gels, and advises against making homemade pesticides with boric acid, because children are at the highest risk; borax can produce boric acid too. If your dog likes to dig in the yard, read our guide to pet-safe ant killers.

How Do You Prevent Ant Hills in Your Lawn?

Preventing ant hills in your lawn comes down to thick, healthy grass, because lawn ants prefer bare, exposed soil for their nests. NDSU Extension says the best strategy for lawns is usually to water regularly and mow high to encourage grass growth and discourage ant nesting.

Mowing Height

Mowing height matters more than most people think. NDSU suggests mowing at three to four inches (about 7.5 to 10 cm). Taller grass shades the soil and fills in the gaps that ants would use to start a nest.

Watering

Watering regularly keeps grass dense and the soil less inviting to ants that like dry, open ground. Keep watering through dry spells, and rake down any small new mound as soon as you see it.

Bare Patches

Bare patches are often where lawn ants set up their nests, since NDSU notes they nest where the soil is exposed. Overseed thin spots, and fill gaps between patio stones and along the driveway edge, two favourite spots for ant hills.

Foundation Clearance

Foundation clearance keeps ant hills from turning into ants in the house. UC IPM recommends keeping plants, grass and mulch at least a foot (about 30 cm) away from the foundation, and Health Canada advises sealing cracks in the foundation and outside walls. If ants have already found their way inside, our guide to getting rid of ants in the house and the ant hub will help you identify them and plan your next steps.