Diatomaceous Earth for Ants: Does It Work and How to Use It Safely

TL;DR

• Yes, but it only kills the ants that crawl through it, and only while it stays dry. It rarely wipes out a colony.
• Use food grade or a registered ant killer dust with a PCP number on the label (Health Canada). Never use pool grade diatomaceous earth in your home.
• Puff a thin, barely visible layer into the cracks and gaps ants travel through, not across open floors. Ants tend to walk around thick piles.
• Keep it dry: it stays active only as long as it is kept dry (Health Canada). Reapply after rain, and after you vacuum or wipe the area.
• Wear a dust mask (Government of British Columbia), gloves and eye protection. Keep the powder in gaps where pets cannot reach it, and out of reach of children.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

The usual mistake with diatomaceous earth for ants is using too much of it. A thick white line along the baseboard looks like a solid barrier, yet ants tend to steer around heaps of powder, while a thin dusting they cross without noticing is what dries them out.

The bag you buy matters as much as the amount you spread. Two products sold under the same name can behave very differently once the dust is in the air: the kind made for pool filters is processed at high heat and is not the one to use in a kitchen.

What Is Diatomaceous Earth?

Diatomaceous earth is a fine, chalky powder made of the fossilized shells of diatoms, and it is mostly amorphous silica. It looks and feels like flour, but under a microscope the particles are sharp and porous. That texture, not a poison, is what makes it work on insects.

What Diatomaceous Earth Is Made Of

Diatomaceous earth is made of crushed microscopic fossils of diatoms, tiny organisms that lived in water, according to Health Canada. The National Pesticide Information Center (NPIC) explains that it is mostly amorphous silicon dioxide, a non-crystalline form of silica, with only very low levels of crystalline silica. The difference between those two forms of silica matters when you choose a product.

Food Grade Diatomaceous Earth

Food grade diatomaceous earth is the purified kind, and it is the one to use against ants. In the US, the FDA lists diatomaceous earth as "Generally Recognized as Safe" for non-pesticide uses such as foods and toothpastes (NPIC). Uncalcined diatomaceous earth typically contains around 1% crystalline silica, according to the New Jersey Department of Health. "Food grade" on the bag tells you about purity, not about how well it kills ants, so you still need to apply it correctly.

Pool Grade Diatomaceous Earth

Pool grade diatomaceous earth is a different product and should never be used for pest control. Pool filter powder is heat-treated (calcined), which turns part of the silica into a crystalline form called cristobalite, according to a US CDC report. The New Jersey Department of Health reports that calcined diatomaceous earth can contain cristobalite, and NPIC notes that long-term inhalation of crystalline silica is linked to silicosis, a serious lung disease. If the bag says pool, filter or swimming pool, leave it in the pool shed.

Registered Ant Killer Dusts

Registered ant killer dusts are diatomaceous earth products approved by Health Canada for use against ants. Health Canada advises you to look for a Pest Control Products (PCP) number on the label, which shows the product has been approved, and to check that the label lists the pest you are treating. For example, Wilson Ant Out Ant Killer Dust, from Quebec-based Premier Tech, carries PCP number 21936 and contains less than 0.1% crystalline silica, according to its safety data sheet. A registered dust also comes with tested directions, which plain garden-centre diatomaceous earth often lacks. For other options, see our roundup of the best ant killers.

Does Diatomaceous Earth Kill Ants?

Diatomaceous earth kills ants that crawl through it, but only those ants, and only while it stays dry. It is a slow, physical killer, so it works best as a barrier on the routes ants already use.

How Diatomaceous Earth Kills Ants

Diatomaceous earth kills ants by drying them out. The powder sticks to an ant's body, absorbs the oils and fats in its waxy outer layer and scratches it, so the ant loses water and dies (NPIC, UC IPM). The ant does not need to eat it, and there is no poison involved. Health Canada describes the same effect: the fossils scratch the ant's outer "skin", causing it to dehydrate.

How Long It Takes

Diatomaceous earth takes anywhere from a few hours to a few days to kill an insect, depending on the insect and the conditions, according to pest control company Orkin. Health Canada notes that it makes ants dehydrate and die; some insects may die within hours of contact, while others take a full day. Expect to see fewer ants on a treated trail after a day or two, not right away.

Why It Rarely Wipes Out a Colony

Diatomaceous earth rarely wipes out a colony because only the ants that touch it die. Most of a colony, including the queen, stays inside the nest, away from your trails, and the powder is not carried back and shared like a bait. Pest control companies such as Terminix and MMPC say the same thing: diatomaceous earth kills the foraging ants it touches (Health Canada notes it dries them out) but is not a reliable way to eliminate a nest. If ants keep coming back, the nest is still active.

Which Ants It Works On

Diatomaceous earth works best on small ants that forage along predictable trails, such as odorous house ants, little black ants and pavement ants, which Health Canada lists among the ants that invade Canadian homes. Product labels do not cover every species. One US label, for example, lists ants "excluding Fire, Harvester, Carpenter and Pharaoh ants."

Two Canadian house ants need a different plan:

• Carpenter ants nest inside wood and can cause structural damage, according to Health Canada. A powder on the surface usually will not reach a nest inside a wall or beam. Read our guide on how to get rid of carpenter ants.
• Pharaoh ants can split into new nests when disturbed (Alberta Health), UC IPM notes that insecticide sprays disperse colonies, and Utah State University Extension advises against dust insecticides because they can spread the ants. Use the bait method in our pharaoh ant guide instead.

How Do You Use Diatomaceous Earth for Ants Indoors?

Using diatomaceous earth for ants indoors means puffing a thin, dry film into the cracks and gaps the ants travel through, not spreading it across open floors. Keeping it in gaps protects your lungs and puts the powder exactly where ants walk.

What You Need

You need four things to apply diatomaceous earth indoors:

• Food grade diatomaceous earth or a registered ant killer dust with a PCP number
• A bulb duster or hand duster (a squeeze bottle with a narrow tip also works)
• A dust mask
• Gloves and eye protection

UC IPM recommends basic protective gear such as gloves, long sleeves and goggles, the Government of British Columbia advises a mask, and the product label may list more.

Where to Apply It

Apply diatomaceous earth where ants travel and hide, not where people walk. Good spots include:

• Cracks and crevices along baseboards and counters
• Behind and under the fridge, stove and cabinets
• Around garbage cans, sink pipes and drains
• Along window frames and door thresholds where ants come in
• Gaps where pipes and wires enter the wall

Follow the ant trail back toward where it disappears into a gap, and dust that gap. Health Canada notes that nests inside wall voids can be treated with dust puffed into the space. If you suspect a nest behind the drywall, our guide to ants in walls explains how to find it.

How Thick to Apply It

Apply diatomaceous earth as a thin layer, barely visible, like a light dusting of flour. The label of one registered product says to "lightly coat a thin layer" where pests hide, and Orkin notes that pests tend to avoid thick piles of the powder, walking around them instead of through them. Do not mix it with water and spray it inside your home: the same label says slurry treatments are not meant for living areas, and Health Canada notes it remains active only as long as it is kept dry.

How Long to Leave It

Leave diatomaceous earth in place, dry and undisturbed, until you stop seeing ants on the treated route. Health Canada says it remains active as long as it is kept dry, so there is no reason to rush the cleanup. Reapply after you vacuum or wipe the area, and if it has been dampened. The label of one registered product says to apply no more than once a week.

How to Clean It Up

Clean up diatomaceous earth with a vacuum or a damp cloth once the ants are gone. The Wilson Ant Out safety data sheet recommends ventilating the area well and vacuuming or sweeping up spills, then rinsing the surface with water. Wear your mask while you clean, since sweeping can put the fine dust back in the air and Health Canada warns not to inhale it, and empty the vacuum outdoors.

How Do You Use Diatomaceous Earth for Ants Outside?

Using diatomaceous earth for ants outside works best as a dry band at entry points and on active trails, renewed after rain. Outdoors, moisture is your main enemy.

Entry Points

Entry points are the most useful place for diatomaceous earth outside. Dust a thin line across door thresholds, along the bottom of window frames, and into cracks in steps, slabs and foundation walls where you see ants going in. An Ask Extension Master Gardener advises against ringing the whole foundation with it, since some nests may be under the house and the powder will not reach them.

Ant Hills

Ant hills can be dusted with diatomaceous earth on a dry day. Health Canada lists it as a non-chemical means of control in cracks and crevices, and the City of Calgary lists placing it around colony locations. Sprinkle a thin layer over and around the opening, without flooding it with powder. Health Canada notes it makes ants dehydrate, so expect it to kill the ants that come out, not the queen deep underground. Our guide on how to get rid of ant hills covers methods that reach the nest.

Moisture

Moisture stops diatomaceous earth from working. Health Canada says it remains active only as long as it is kept dry, and one US label states that it is less effective when relative humidity is high. Reapply after rain, heavy dew or watering the garden, and favour sheltered spots such as under deck boards, along the house under the eaves or inside door frames.

Beneficial Insects

Beneficial insects can be killed by diatomaceous earth too, because it is not selective. Bees, ladybugs and other helpful insects that crawl through it can dry out just like ants. Keep it off flowers and blooming plants, and limit it to trails, entry points and ant hills.

Is Diatomaceous Earth Safe for People and Pets?

Diatomaceous earth is low in toxicity for people and pets, according to Health Canada, but its dust irritates the lungs and eyes, so how you apply it matters. Health Canada describes it as non-toxic to humans and pets and warns not to inhale the dust when applying it.

Breathing the Dust

Breathing diatomaceous earth dust can irritate your nose and nasal passages, and extremely large amounts may cause coughing and shortness of breath (NPIC). That is why an Ask Extension Master Gardener advises against dusting it around living spaces indoors. Wear a dust mask, keep the powder in cracks rather than on open floors, ventilate the room, and avoid applying it on a windy day outside.

Eye Irritation

Eye irritation is the other common effect, because the particles are abrasive. One registered label warns that it "causes moderate eye irritation," so wear eye protection and avoid rubbing your eyes during application. On skin, it can cause dryness and irritation (NPIC), so gloves help too.

Pets

Pets can be exposed if they can reach the powder, NPIC notes. Apply it in gaps and behind appliances where a cat or dog cannot lie in it, lick it or sniff it up, and keep pets out of the room until the dust settles. If you want other options that are gentler around animals, see our guide to pet-safe ant killers.

Children

Children should not play near treated areas, and registered labels and safety data sheets, such as those for Harris and Wilson Ant Out, say to keep the product out of reach of children. NPIC notes that children may be more sensitive to pesticides in general, although there are no data showing extra sensitivity to diatomaceous earth specifically. Store the bag closed and up high, and choose cracks and crevices over play areas.

When Should You Use Baits Instead of Diatomaceous Earth?

Baits are the better choice when you need to kill the whole colony, because worker ants carry them back to the nest and feed them to the queen (UC IPM). You can keep using diatomaceous earth at entry points while you bait, as long as you keep it away from the bait stations and the trails leading to them, so the ants keep reaching the bait.

Baits for Whole Colonies

Baits for whole colonies work slowly on purpose. Health Canada explains that a bait must act slowly enough to be shared with every member of the nest. Its advice for homeowners:

1. Place bait stations directly in the path of foraging ants, out of reach of children and pets.
2. Use plenty of stations, and try two different baits at the same time, which Health Canada says gives better results.
3. Keep baits available for at least two weeks, and repeat if needed.
4. Do not spray insecticides while baiting, or the bait will not work.

Borax Baits

Borax baits, made with boric acid or borax, are the most common colony-level option, and Health Canada says boric acid baits are generally of low toxicity to other animals. Diatomaceous earth is a contact barrier while borax is a bait the ants carry home, so many people use both: baits for the nest, diatomaceous earth for entry points. Our comparison of diatomaceous earth vs borax explains which to choose and how to set borax baits.

When to Call a Pest Control Professional

Calling a pest control professional makes sense when you see signs of carpenter ants (such as piles of sawdust, according to Health Canada), when you have pharaoh ants in an apartment building, or when weeks of baiting and dusting have not reduced the trails. A professional can find and treat nests inside walls that you cannot reach. You can get a quote from a recommended local exterminator through Pest Agent's referral form, or start with our complete guide on how to get rid of ants. Living on the road? The same rules apply in a small space, and our guide to ants in a camper adapts them.