Diatomaceous Earth (DE) is a naturally occurring powder used for pest control. This fine dust is composed of the fossilized remains of diatoms, which are microscopic, single-celled aquatic algae. The shells are primarily made of silica, which gives DE its insecticidal properties. DE provides an effective alternative to chemical insecticides, targeting crawling insects in the home and garden through a purely physical action, meaning pests cannot develop resistance.
The Physical Mechanism of Pest Death
DE’s effectiveness against crawling insects is entirely mechanical. The crushed diatom fossils possess microscopic, sharp edges that are harmless to mammals but devastating to small pests. As an insect crawls across the dust, the sharp silica particles abrade the protective waxy layer of its exoskeleton, known as the cuticle.
This slicing compromises the insect’s outer defense, which is essential for retaining moisture. Once the cuticle is breached, the porous DE absorbs the epicuticular lipids and body fluids through the damaged areas. This rapid loss of moisture causes the insect to dehydrate quickly, a process known as desiccation. The pest cannot recover from this fluid loss, leading to death, usually within a day or two of initial contact.
Food Grade Versus Filter Grade
It is important to understand the difference between the available grades of Diatomaceous Earth. Only “Food Grade” DE should be used for household and garden applications, particularly where people or pets may be present. This grade is composed of amorphous silica, meaning the particles have no definite crystalline structure. Food Grade DE is uncalcined (not heat-treated) and contains less than one percent crystalline silica.
Conversely, “Filter Grade” or “Pool Grade” DE is heat-treated through calcination to improve filtration. This treatment converts amorphous silica into crystalline silica, which is a known inhalation hazard. Due to its high crystalline silica content, filter grade DE is unsuitable for general pest control and should only be used for industrial purposes, such as pool filtration. Regardless of the grade, wearing a dust mask and gloves during application is prudent, as inhaling any fine dust can irritate the lungs.
Practical Application for Pest Control
Effective use of Food Grade DE depends on proper application technique and placement. The powder must be applied as a very thin, almost invisible layer, often requiring the use of a bulb duster or similar puffer tool. If the layer is too thick, crawling pests will instinctively avoid traversing the pile, rendering the treatment ineffective.
The goal is to place the fine dust in areas where insects are known to travel or hide, such as cracks, crevices, and wall voids. Applying a narrow line along baseboards, under sinks, behind appliances, and around window frames and door thresholds is effective.
Common pests controlled by this method include:
- Ants
- Cockroaches
- Bed bugs
- Fleas
- Silverfish
DE only works when it is completely dry, so it must be reapplied if it becomes wet from rain, humidity, or cleaning. For outdoor perimeter defense, focus on dry areas and reapply after any significant moisture exposure.