Diatomaceous Earth (DE) is a natural substance used widely for pest control, composed of the fossilized remains of diatoms, which are microscopic, single-celled aquatic organisms. These ancient skeletons are primarily made of silica, which is ground into a fine, soft powder that feels like talc to humans. This article explores the unique physical method by which DE controls pests and identifies the specific insects it eliminates, along with those that are unaffected.
How Diatomaceous Earth Kills Insects
Diatomaceous earth functions purely as a mechanical insecticide, not a chemical poison, meaning insects cannot develop resistance to it. The particles of DE reveal sharp, jagged edges, which physically slice through the protective, waxy outer layer of the insect’s exoskeleton, known as the cuticle. This waxy layer prevents water loss and maintains the insect’s internal moisture. Once this barrier is breached, the DE particles act as powerful absorbents, drawing out the insect’s body fluids and essential oils. This rapid, uncontrolled loss of internal moisture leads to desiccation, which is the ultimate cause of death for the pest.
Pests Vulnerable to Diatomaceous Earth
The effectiveness of DE is concentrated on crawling insects with soft or vulnerable exoskeletons that must come into direct contact with the powder. It is mandatory to use only food-grade DE, which is largely amorphous silica, for pest control in homes and gardens. Filter-grade DE, often used for pools, contains hazardous crystalline silica and must never be used.
Household Pests
Common household pests with high vulnerability to food-grade DE include:
- Bed bugs
- Fleas
- Cockroaches
- Ants
- Silverfish
- Carpet beetles
- Crickets
The powder is effective when strategically dusted into cracks, crevices, and along baseboards where these pests hide and travel, providing a long-lasting physical barrier.
Garden Pests
In the garden, DE controls many soft-bodied pests that damage plants, such as aphids, mites, and thrips. It is also effective against various stages of harder-shelled garden pests, including the larvae of squash bugs, cucumber beetles, and small caterpillars. The desiccant action is also utilized against pests that are not true insects, like spiders, ticks, centipedes, and millipedes. For these pests, the key is ensuring they move through the powder, which takes between 24 hours and a few days to be lethal.
Insects and Organisms Not Affected
Diatomaceous earth is not a universally effective method, as certain insects and organisms are less susceptible to its mechanical action. Flying insects, such as moths, gnats, and houseflies, are not controlled by DE because they do not spend enough time crawling across treated surfaces to accumulate the powder. Larger, mature insects with thick, hardened exoskeletons, such as adult beetles and larger cockroaches, can also resist the abrasive damage to their cuticles.
Organisms that thrive in moist environments are protected from the drying effects of DE. This includes slugs and snails, whose slimy outer layer prevents the powder from adhering to their bodies. Earthworms are also unaffected because they live beneath the surface in damp soil, which neutralizes the DE’s desiccant property. Because DE is non-selective, application should be avoided on flowers or in areas where pollinators are active, as it can harm beneficial insects like bees and ladybugs if they come into direct contact with the dust.
Effective Application and Safety Guidelines
For diatomaceous earth to work, it must remain completely dry, as contact with moisture causes the particles to clump and lose their abrasive and absorbent qualities. Correct application involves using a handheld duster to create a very thin, almost invisible layer of powder over the desired surface. A thick, visible pile of DE is counterproductive, as pests will walk around a large mound of powder.
Effective areas for application include cracks, crevices, wall voids, and under appliances, focusing on the pathways where pests travel. If applying outdoors, reapplication is necessary after any rain or heavy dew to maintain efficacy.
When handling the fine powder, wear a dust mask or respirator, as inhaling the dust can irritate the nasal passages, throat, and lungs. While food-grade DE is considered safe for use around pets and children, wearing gloves is recommended to prevent skin dryness.