Diatomaceous Earth (DE) is a popular, natural pest control product derived from the fossilized remains of tiny, aquatic organisms called diatoms. These remains are primarily composed of silica, which is ground into a fine powder. DE can be harmful to bees, especially if it makes direct contact with the insect. Because DE acts through a physical mechanism rather than a chemical toxin, it is non-selective, meaning it can harm any insect, including beneficial ones like bees.
Composition and Mechanism of Diatomaceous Earth
Diatomaceous Earth is composed of amorphous silica, the skeletal remnants of ancient, single-celled algae called diatoms. When these organisms died, their hard, porous shells settled in sediment layers, forming a sedimentary rock called diatomite. The mined powder is exceptionally abrasive and highly absorbent due to the microscopic, sharp, jagged edges of the diatom skeletons.
DE works as a mechanical insecticide against pests with an exoskeleton. When an insect crawls over the powder, the microscopic particles abrade the protective outer layer, known as the waxy cuticle. This layer contains lipids and oils essential for moisture retention. The absorbent nature of the DE then rapidly draws out these fats and oils, causing the insect to lose internal body fluid. This dual action leads to lethal dehydration, or desiccation, which is entirely a physical process.
It is important to differentiate between two main types: Food Grade DE and Filter Grade DE. Food Grade DE consists mostly of amorphous silica and contains less than 1% crystalline silica, making it suitable for pest control. Filter Grade DE is heat-treated (calcined), which converts the silica into a form containing high concentrations of crystalline silica. This grade is harmful if inhaled and should never be used for pest control.
Specific Vulnerability: How Diatomaceous Earth Harms Bees
Bees possess an exoskeleton protected by a waxy cuticle that is susceptible to DE’s mechanical action. Because DE is non-selective, it damages the bee’s protective layer upon contact, just like any other insect. Foraging bees can be exposed by landing on treated surfaces or flying through airborne dust.
A bee’s body is covered in fine hairs that may offer some initial protection. However, if a bee picks up DE, its natural grooming behavior can worsen the situation. As the bee attempts to clean the dust, the abrasive particles are rubbed against the exoskeleton, accelerating damage to the waxy layer.
The risk varies depending on the species. Flying honey bees primarily risk exposure when foraging on treated flowers or dusty surfaces. Ground-nesting bees, such as mason bees, face a higher risk because they crawl through ground-level areas often targeted by DE applications. If a bee covered in DE returns to the hive, the abrasive powder can be introduced into the colony, potentially affecting other bees or larvae.
Mitigation Strategies: Using Diatomaceous Earth Safely
Protecting pollinators requires applying DE in a targeted manner that minimizes direct contact with bees and flowering plants. Adjusting the application timing is highly effective. Apply the powder late in the evening or at night when most bees are inactive. This allows the DE to settle before morning activity resumes.
Targeted application is crucial. DE should only be applied to areas where pests are present, such as ant trails or the base of plants. Avoid dusting flowers, blooms, or leaves where bees collect nectar or pollen. When treating plants, aim for the soil around the base to deter crawling pests.
The application method can also reduce risk. Instead of broadcasting a heavy layer, use a fine, barely visible film of dust. Alternatively, mix Food Grade DE with water to create a sprayable slurry. This wet application minimizes airborne dust clouds that could drift onto non-target areas. Always read the product label to ensure the product is Food Grade.