Diatomaceous earth (DE) is a naturally occurring powder used for pest control in homes and gardens. This substance is derived from the fossilized remains of diatoms, microscopic, single-celled aquatic organisms. The resulting fine, chalky powder is primarily composed of amorphous silica. For household and garden use, choose food-grade DE, as industrial versions contain higher levels of crystalline silica, which can be hazardous when inhaled. The unique physical structure of this powder is the basis for its effectiveness against crawling insects.
How Diatomaceous Earth Works
Diatomaceous earth functions as an insecticide through a physical, non-chemical mechanism, preventing pests from developing resistance. Under a microscope, the powder is composed of sharp, jagged particles. These remnants of diatom shells act as abrasive agents against pests.
The mechanical action begins when an insect crawls across the powder, causing the microscopic edges to damage its protective outer layer, the exoskeleton or cuticle. This physical disruption is accompanied by the powder’s highly absorptive nature. DE absorbs the protective waxy layer (made of lipids) from the insect’s cuticle.
Removing this waxy layer compromises the insect’s ability to retain moisture, leading to uncontrolled water loss. The pest dies from fatal dehydration, a process called desiccation, typically within 24 to 72 hours. Since the method relies on physical abrasion and moisture absorption, it is considered a mechanical killer.
Pests Controlled by Diatomaceous Earth
Diatomaceous earth is most effective against small, crawling insects with a hard exoskeleton that move through treated areas. Its abrasive and drying properties are lethal to common household pests. DE is highly effective against bed bugs, fleas, and cockroaches, which hide in cracks and crevices where the dust can be applied.
In the garden, DE controls many pests that feed on plants.
Common Garden Pests
- Aphids
- Thrips
- Cucumber beetles
- Potato beetles
- Earwigs
- Silverfish
- Mites
These pests are all susceptible to the desiccation process. Successful elimination relies on direct contact, as the insect must physically pick up the dust particles. Pests with a tough, waxy cuticle or those that move slowly, like ants and carpet beetles, are good candidates for control. The time it takes to kill a pest varies based on its size and the thickness of its exoskeleton.
Pests Diatomaceous Earth is Ineffective Against
The mechanical action of diatomaceous earth is not universally effective, having limitations based on an organism’s biology and behavior. Pests that lack a hard, waxy exoskeleton are not susceptible to physical damage and dehydration. For example, soft-bodied creatures like slugs and snails are not reliably controlled by DE because their moist, slimy coating acts as a protective barrier against the powder’s drying effects.
Flying insects, such as house flies, wasps, and mosquitoes, are largely unaffected. They do not crawl across dusted surfaces long enough to accumulate a lethal dose, and are too fast and agile for static dust application. Furthermore, very large or mature insects with exceptionally thick exoskeletons, such as some large beetles or certain cockroaches, may tolerate minor exposure and survive the initial abrasion.
The presence of moisture also renders DE temporarily ineffective. If the powder gets wet from rain, dew, or high humidity, its absorptive capacity is compromised. It stops working until it completely dries out, making outdoor application challenging in wet climates.
Safe and Effective Application Methods
For diatomaceous earth to work, it must be applied as a very fine, thin layer that is barely visible. Applying a thick, noticeable pile of powder is counterproductive, as pests will walk around a large mound rather than through it. A thin application, often achieved using a bellows duster, a bulb duster, or a flour sifter for small areas, ensures the pest contacts the dust without being deterred.
For indoor pest control, the dust should be strategically placed in cracks, crevices, behind appliances, and along baseboards where crawling insects travel. After pests are eliminated, the remaining powder should be cleaned up, typically by vacuuming. When applying DE outdoors, dust the perimeter of a home or garden beds during dry weather; moisture will require reapplication.
Safety precautions are important to protect the respiratory system from the fine particles. While food-grade DE is non-toxic, inhaling the dust can irritate the lungs. Wearing a dust mask or respirator, especially when dusting large areas, is advisable to prevent inhalation. Keep children and pets away from treated areas until the dust has settled or been cleaned up.