Diatomaceous earth kills a wide range of crawling insects, including bed bugs, cockroaches, ants, fleas, ticks, silverfish, and termites. It also works against grain-storage pests like weevils and flour beetles, and even some garden pests like aphids and caterpillars. The key requirement is that the pest must come into physical contact with the powder for it to work.
How Diatomaceous Earth Kills Insects
Diatomaceous earth (DE) is made from the fossilized remains of tiny aquatic organisms called diatoms. Under a microscope, the particles have sharp edges and a highly porous structure. When an insect crawls through DE, those edges scratch the thin waxy coating on its exoskeleton. That coating is what keeps moisture locked inside the insect’s body. Once it’s damaged, DE also absorbs the waxy oils directly through its pores, accelerating the process. The insect loses water rapidly and dies from dehydration.
This is a purely mechanical process, not a chemical one. That distinction matters because insects can’t develop resistance to physical damage the way they can to chemical pesticides. It also means DE works on virtually any insect with an exoskeleton, as long as the powder stays dry and makes contact with the body.
Household Pests
DE is most commonly used indoors against cockroaches, bed bugs, ants, silverfish, fleas, and termites. German cockroaches, American cockroaches, and Oriental cockroaches are all susceptible. Pharaoh ants, a notoriously difficult indoor species, also appear on the list of pests DE can control. Silverfish, which thrive in dry indoor environments, are particularly vulnerable because they live in exactly the conditions where DE performs best.
For bed bugs, the timeline depends heavily on the quality of the product and how much contact occurs. In a 2024 study comparing different DE products against bed bugs, a professional-grade DE achieved 100% kill rates within two to four days of continuous exposure. A pet-litter grade DE took eight to ten days to reach the same result. A supermarket-grade product killed fewer than 30% of bed bugs even after ten days. Even brief exposure matters: bed bugs that walked through professional-grade DE for just ten minutes and were then moved to a clean surface still reached 65 to 100% mortality within ten days.
Stored-Food and Pantry Pests
DE has a long history of use in grain storage, where it protects against beetles and weevils that infest cereals, flour, and rice. The pests it targets in this category include rice weevils, granary weevils, maize weevils, red flour beetles, confused flour beetles, lesser grain borers, rusty grain beetles, and khapra beetles. Both adult insects and larvae are affected, though adults with harder exoskeletons sometimes take longer to die than soft-bodied larvae.
Food-grade DE can be mixed directly into stored grain at low concentrations. This is one of its oldest agricultural applications and remains popular in organic farming because it leaves no chemical residue.
Garden and Crop Pests
Outdoors, DE works against soft-bodied pests like green peach aphids, armyworms, and other caterpillar species. Ticks, including cattle ticks, and various mite species are also susceptible. Poultry keepers use DE against red mites and northern fowl mites, which infest coops and feed on birds.
Garden use comes with a tradeoff. DE is non-selective, meaning it can also harm beneficial insects like pollinators if they come into direct contact with it. Applying it in targeted spots rather than broadcasting it widely helps reduce that risk.
Why Humidity and Moisture Matter
DE only works when it’s dry. Moisture clogs the porous structure of the particles and prevents them from absorbing the waxy coating on insects. In laboratory tests, higher humidity levels (around 75%) reduced DE’s effectiveness against grain pests compared to drier conditions (55% humidity), though some formulations held up better than others.
The good news is that DE doesn’t break down permanently when it gets wet. Once it dries out, it regains its insecticidal properties. It can go through unlimited wet-dry cycles without losing effectiveness. Outdoors, you’ll need to reapply after rain or heavy wind simply because the lightweight powder gets washed or blown away. Indoors, it lasts indefinitely as long as it remains in place and stays dry.
How to Apply It
For indoor use, apply a thin, even layer of DE in cracks, crevices, behind appliances, along baseboards, and in other areas where pests travel. A heavier pile is actually less effective because insects will walk around it rather than through it. A fine dusting they can’t avoid is the goal. Hand-pump dusters work well for reaching tight spaces.
DE can also be mixed with water to form a slurry for easier application in hard-to-reach areas. While wet, it has no insecticidal effect, but once the water evaporates, the dried residue works just as it would if applied dry. This method is useful for coating surfaces evenly or applying DE to vertical spaces where dry powder won’t stick.
Wear a dust mask during application. Inhaling the fine particles can irritate your nose, throat, and lungs. The amorphous silica in food-grade DE causes only mild, reversible lung irritation and clears from lung tissue quickly. But minimizing inhalation is still a smart practice, especially during application when airborne dust levels are highest.
Food Grade vs. Pool Grade
This is a critical distinction. Food-grade DE contains less than 1% crystalline silica and is the only type appropriate for pest control, gardening, or any application involving people or animals. Pool-grade (also called filter-grade) DE has been heat-treated in a process called calcination, which converts the silica into a crystalline form at much higher concentrations. Crystalline silica is a serious respiratory hazard linked to silicosis, chronic bronchitis, and other lung diseases with long-term exposure. Pool-grade DE should never be used for pest control.
Food-grade DE is considered practically non-toxic to fish, aquatic invertebrates, birds, and other wildlife. Some products are labeled for direct use on dogs and cats to control fleas and ticks, though you should follow the specific product label for application guidance. Keep the powder away from your pet’s face to avoid eye and respiratory irritation.
What DE Won’t Do
DE is not a fast-acting solution. Even under ideal conditions, it takes hours to days to kill insects, and often longer for larger or harder-bodied species. It won’t kill pests that never touch it, so flying insects are largely out of reach unless they land and crawl through treated areas. It’s also ineffective against pests that live in wet environments, since moisture neutralizes the drying mechanism.
For heavy infestations of bed bugs, cockroaches, or termites, DE works best as one tool within a broader strategy rather than a standalone fix. Its strength is as a long-lasting, chemical-free barrier that continues working for as long as it stays in place.