Diatomaceous Earth: What It Really Kills

Diatomaceous earth is a soft white powder made from the fossilized skeletons of diatoms. It kills insects by pulling the oils and fats off their outer shell until they dry out and die. Nothing gets poisoned, and nothing has to be eaten. Two things decide whether it works in your house or your garden. The grade you buy, and how long the insect stays in the dust.

Grade is not a small detail. In a 2024 trial on 1,200 bed bugs, dust sold by a pest management company killed 100% of them by day 10 under nonstop contact, while supermarket DE powder reached 15%. Both bags look like the same white flour when you open them. Under an electron microscope the cheap one had melted, fused diatom skeletons, and the good one had sharp intact ones.

This is not a folk remedy someone made up on a forum. The first products with silicon dioxide in them were registered as pesticides in 1960. More than 150 products are now cleared for use inside buildings and outside on farms, in gardens and in pet kennels. The FDA lists diatomaceous earth as Generally Recognized as Safe. Silica makes up 26% of the earth's crust by weight, so what you spread is common rock, ground fine.

Buy food grade diatomaceous earth. It is mostly amorphous silica, and the crystalline form is the one tied to lung disease in miners who breathed it for years. Then use it like the contact insecticide it is. It kills only what walks through your dust, it repels nothing, and it quits the moment it gets damp. Put it where insects keep walking, because contact time is what kills them.

The ants came in along the kitchen door threshold, a thin brown line from the frame to the dog bowl. I lined the sill with dust, one unbroken white band, and left it there. The trail kept moving for two more days. I never got a count of what the dust reached and what missed it entirely. Diatomaceous earth for ants works on contact and nothing else. The dust is a contact insecticide that is not poisonous, and it does not have to be eaten, so it reaches only the bugs that walk through it and stay in it.

What pests does diatomaceous earth kill? Sort the answer into three levels of proof, because the gap between them is wide. At the top sit the pests with measured kill rates from controlled trials. In the middle sit the pests named on pesticide registrations, which tell you a product may be sold for that bug and nothing about how many die. At the bottom sit the pests a university guide talks about, where you get discussion and no numbers at all.

NPIC names bed bugs, cockroaches, crickets, fleas, ticks and spiders as registered targets, and some products are labeled for use straight on dogs and cats. That matters if you are buying diatomaceous earth for fleas for your dog or your cat. Read the label on the bag rather than a recipe from a blog. Diatomaceous earth for bed bugs carries the hardest numbers of the whole list, and even there the brand set the result, at 100% kill against 15% for a supermarket bag.

UC IPM puts the dust in its Pest Notes for carpenter ants, carpenter bees, carpet beetles, cockroaches, silverfish and firebrats, and snails and slugs. That is coverage, not proof. Those pages show you where the powder fits in a treatment plan. None of them give you a kill rate you can plan around.

So how does diatomaceous earth work? It dries insects out. That is the plain fact of the mechanism, and none of it involves poison. A bug never has to eat the dust. It works the moment the bug touches it, which makes this a contact insecticide and not a toxin. The insect only has to walk into your powder and pick the particles up on its legs and body.

Two agencies describe the same kill side by side, in slightly different words. The National Pesticide Information Center puts it one way. The powder absorbs the oils and fats from the cuticle of the insect exoskeleton, the waxy layer that seals water in. UC IPM puts it another way. The same dust absorbs moisture and scratches the exoskeleton. Picture blotting paper pressed on a waxed jacket. The paper pulls oil out of the wax, and the sharp edges score what is left, so water gets out by both routes at once.

That chain has a name. Desiccation is death by drying, and it puts your powder in the desiccant dust family rather than with poisons a pest has to swallow. It also explains the storage and reapplication rules you will meet later. The material remains effective only while it stays dry and undisturbed. Once it soaks up rain, dew or sprinkler spray, your barrier does nothing until it dries out or you spread fresh dust.

Three weeks in, the bugs were still walking over the powder I lined across the sill. That bag was food grade diatomaceous earth from a farm store, bought because every guide says to buy food grade. Controlled testing later put a number on that kind of letdown. A supermarket-sourced diatomaceous earth reached only 15% bed bug mortality by day 10, with the insects held on the treated surface the whole time.

Does diatomaceous earth actually work? That depends on the bag. Grade sorts the powder by crystalline silica content, and food grade holds very little of it. Pool grade is calcined diatomaceous earth. Makers heat it until part of the silica turns crystalline, which is why it belongs in a filter and never on your baseboards. The split protects your lungs. It says nothing about whether the dust kills bugs.

A 2024 study in the journal Parasite tested eight dusts against two field-collected bed bug colonies. Under permanent exposure, professional pest-management dust hit 100% mortality by day 10. A litter-conditioner dust also reached 100%, but not until somewhere between day 8 and day 10. Supermarket dust stalled at 15%. The untreated control killed nothing, 0%.

Electron microscopy showed the reason. The professional dust still had intact diatom frustules of amorphous silica. The two weak powders showed melted or fused skeletons, a sign of flux-calcination and partial change to cristobalite. Structure drove the second-hand kill too. Exposed bed bugs mixed back in with clean nymphs passed on 85% and 95% mortality from the professional dust, against 30% and 10% from the supermarket bag.

Diatomaceous earth brands differ far more than the labels let on. The bag prints the grade and says nothing about the structure, and structure is what sets DE effectiveness. Buy from a pest-control supplier, not a grocery aisle. Give a new powder unbroken contact and days, not hours, before you write it off.

Why does one white powder belong in a feed shed while the other belongs only in a pool filter? Heat is the whole difference. Makers roast pool and filter products at high temperature. That heat fuses the glassy diatom skeletons and pushes part of the silica toward cristobalite, a crystalline form. Food grade diatomaceous earth does not go through that oven, so the shells stay intact and the silica stays amorphous.

The two forms do not carry the same risk. IARC puts crystalline silica in Group 1, carcinogenic to humans, for workers who breathe it in as quartz or cristobalite. Amorphous silica sits in Group 3, not classifiable. Most of the mineral in a pest control bag is the amorphous kind, with only very low levels of the crystalline form. One grain protectant lists its mix at under 0.9% total crystalline silica, 10% silica gel and 90% amorphous silicon dioxide. That is the profile you want in a bag you keep near feed or a bed frame.

So skip any bag that just says diatomaceous earth and leaves it there. You want food grade on the front and a pesticide label on the back that names the pests and the places you plan to treat. Some bags also carry an OMRI listed mark, which covers use in certified organic growing rather than the grade itself, so read for both. Pool grade diatomaceous earth cleans water, and calcined diatomaceous earth belongs in a filter tank, not on a coop floor or under a mattress seam.

Is diatomaceous earth safe? For a household that reaches for it now and then, the published record is reassuring in places and disputed in others, with limits worth naming. Most DE is amorphous silica, and IARC rates that form Group 3, not classifiable for cancer in people. Crystalline silica breathed on the job as quartz or cristobalite sits in Group 1. That split is the whole reason the grade on the bag matters, because the pesticide products you buy hold only very low crystalline levels.

The animal data is thin, and it points one way. Rats fed a diet of 5% diatomaceous earth for 90 days gained weight faster, and that was the only effect recorded. Guinea pigs that breathed it for two years ended up with slightly more connective tissue in the lungs. Nothing showed up before the two-year mark.

NPIC ties the amorphous form to mild, reversible lung inflammation and nothing past that. Akhoundi and colleagues read the same material and land somewhere else. They argue the particles settle in the bronchi, alveoli and lymph nodes and never leave. The list they give runs from silicosis to lung cancer and on to nonmalignant respiratory disease. Three things reconcile the two positions: crystalline content, long exposure, and work done in mines.

The silicosis literature describes miners and plant workers breathing dust across years of shifts. The documented diatomaceous earth inhalation risk traces back to that picture, not to the bag you keep in the garage. That is scale, not a clean bill of health. Children may be more sensitive to pesticides in general. No data so far conclude they react more to this one, so treat it as an open question rather than a green light.

Placement decides whether the dust does anything at all. In the French bed bug study, professional-grade dust killed 100% of the bugs under permanent exposure, where the insects had nowhere to walk that was not treated. Cut that contact to 10 minutes and day-10 mortality landed at 100% in one colony and 65% in the other. The litter-conditioner dust in the same test fell from 100% down to 50% and 20%. How to use diatomaceous earth comes down to one choice. Put it where insects stop and stay a while.

How to apply diatomaceous earth in the garden follows the same rule. Dust the soil line, the stem bases and the boards that crawling pests travel along. Leave the open flowers alone. UC IPM rates the honey bee hazard as Low and asks for no bee precaution beyond the label. But the dust kills on contact, whatever walks through it, so keeping it off blooms costs you nothing and protects pollinators. No source gives a rate per square foot for home use, so every question about amount ends at the product label.

By 6 a.m. the white line along my raised beds had turned to gray paste. I had laid it down dry at dusk. Humid summers do that, because overnight dew settles on the soil and the boards long before sunrise, and paste has no dry edges left to abrade anything. Diatomaceous earth and moisture cancel each other out. The dust works only as long as you keep it dry and undisturbed.

Plan to reapply after rain, after a heavy dew and after the sprinklers run. Let the label tell you how soon. Indoors that problem mostly goes away. The same dust that quits on you in a wet bed keeps working in a dry wall void or along a baseboard, as long as nothing wets or sweeps it.

Work in order. Identify the pest first, because placement changes a lot between a cockroach that runs the base of a wall and an aphid sitting on a leaf. Then buy a food grade diatomaceous earth whose label covers the site you plan to treat. Lay down a thin, even film along the routes insects travel and inside the cracks where they rest. Keep it dry and undisturbed, and give it several days before you judge it. Vacuum or sweep the dust away once the pest is gone.

The buying check is the fast part. The bag has to say food grade, and that phrase is doing real work. It splits the amorphous silica product from pool filter powder that has been heated into crystalline silica. Quality still swings hard inside that grade. In a 2024 bed bug trial, dust from a pest management company killed 100% of the bed bugs by day 10 under constant exposure, while a supermarket product reached 15%.

None of the eight dusts in that trial repelled bed bugs at all. This is not a barrier that turns pests away. It is a slow contact killer, and it only reaches the insects that walk into the dust and stay in it, so contact time decides the outcome. A thin unbroken line across a doorway that insects have to cross beats a thick pile off to one side. It is also the wrong tool anywhere the surface cannot stay dry, because wet powder does nothing and you have to reapply after rain.

As organic pest control goes, diatomaceous earth earns a spot in the rotation without carrying a whole program on its own. The two things the published trials measured moving were the formulation you buy and the contact time you create. The brand story on the bag and the promise of an overnight fix sit outside what the evidence supports.