Diatomaceous Earth (DE) is a naturally occurring, soft, sedimentary rock crumbled into a fine, off-white powder. This substance is composed almost entirely of the fossilized remains of diatoms, which are microscopic, single-celled algae from ancient waterways. The unique structure of these fossils forms the basis of DE’s utility as a pest control agent against various mite populations. This article explores how diatomaceous earth works to eliminate mites and the appropriate methods for its safe application.
The Physical Mechanism of Diatomaceous Earth
Diatomaceous earth’s ability to kill small arthropods is purely physical and not chemical. The powder consists of silica-based skeletons that, when viewed under a microscope, appear as razor-sharp, abrasive edges. These microscopic shards feel like a fine powder to human touch but act like broken glass to a mite.
When an arthropod crawls across a layer of DE, the sharp edges scrape and damage the waxy, protective outer layer of its exoskeleton. This physical disruption compromises the pest’s natural barrier against moisture loss. Diatomaceous earth also possesses a high degree of porosity, which allows it to absorb the oils and fats from the damaged cuticle.
The combined effect of abrasion and absorption causes the mite to rapidly lose essential body fluids, a process known as desiccation. Since the pest cannot restore this lost moisture, death typically occurs within a period ranging from a few hours to a couple of days, depending on environmental conditions. Unlike traditional chemical pesticides, arthropods cannot develop resistance to this mechanical mode of action.
Specific Effectiveness Against Mite Species
Diatomaceous earth is highly effective against small, soft-bodied organisms like mites. Its success, however, is heavily dependent on the mite species and its habitat, as direct contact with the dry powder is required for it to work.
Pest mites that live on surfaces, such as spider mites, poultry mites (red mites), and bird mites, are effectively controlled by direct contact with DE. In agricultural or poultry settings, applying DE to coops, nests, or plant foliage ensures the mites must crawl through the dust to reach their hosts, leading to desiccation. For garden pests like spider mites, the challenge is application, as the mites often hide on the moist undersides of leaves where dry DE powder does not adhere well.
The limitations of DE become apparent when considering house dust mites, which are a major source of indoor allergens. These mites live deep within fabrics, mattresses, and carpets, thriving in high-humidity environments. Since DE loses its efficacy when wet and is difficult to distribute throughout dense fibers, it is not a practical solution for their control. While some studies suggest DE can reduce environmental moisture, applying it for direct dust mite eradication in a home environment is often impractical and poses an inhalation risk.
Safe Handling and Application Methods
When selecting diatomaceous earth for pest control, use only the “Food Grade” variety. This type contains amorphous silica and is purified for safe use around humans and animals. Avoid “Filter Grade” (or pool grade) DE, which contains crystalline silica that can be hazardous when inhaled.
Safety during application is paramount, primarily to avoid inhaling the fine dust particles, even the food-grade type. Individuals applying the powder, especially those with pre-existing respiratory conditions, should wear a dust mask and gloves to prevent lung irritation. Keep children and pets away from the area until the dust has fully settled.
For maximum effectiveness, DE must be applied as a very thin, barely visible layer, as thick piles can deter mites from crawling over it. The powder must remain completely dry to maintain its abrasive and desiccating properties. If it becomes damp from rain, dew, or humidity, its effectiveness is significantly reduced, requiring reapplication once the area dries. A duster tool or fine flour sifter can help ensure the powder is distributed lightly and evenly in cracks, crevices, and along entry points where mites are likely to travel.