Diatomaceous Earth (DE) is a popular, naturally derived substance used for non-chemical pest control. This fine, white powder is highly effective against various insect pests, leading many to adopt it for use around their properties. Concern arises when considering beneficial insects like the honey bee, whose populations are already under pressure. Because DE kills insects through a physical process rather than a chemical one, its safety near active bee colonies and foraging areas is questioned. This article clarifies the composition of DE, explains the mechanism by which it eliminates pests, and provides methods for its safe application to protect honey bees.
Understanding Diatomaceous Earth
Diatomaceous Earth is a soft, sedimentary rock easily crumbled into a fine powder, composed primarily of silicon dioxide, or silica. This material consists of the fossilized remains of diatoms, which are single-celled algae that constructed intricate, hard shells over millions of years. When harvested and milled, these microscopic skeletons form a highly porous, absorbent powder.
It is important to differentiate between the grades of this product, as not all are safe for use as an insecticide. Only Food Grade Diatomaceous Earth is suitable for pest control applications, containing less than one percent crystalline silica. Other industrial forms, such as Filter Grade or Pool Grade DE, are often heat-treated in a process called calcining, which significantly increases the concentration of crystalline silica. This calcined form is hazardous and should never be used for pest management or around animals.
The Mechanism: Why DE Kills Insects
The effectiveness of Food Grade DE against insects is due to a physical action, not toxic chemical properties. Under a microscope, the tiny silica particles resemble shards of glass with razor-sharp edges. When an insect crawls across the powder, these abrasive edges mechanically damage the insect’s protective outer layer, known as the cuticle.
The insect cuticle is a waxy, lipid-rich layer that prevents internal moisture loss. Once the microscopic particles pierce this barrier, the highly absorbent DE draws out the protective lipids and internal body fluids. This rapid moisture loss is called desiccation, and it is the cause of death for the pest. Because the mechanism is physical, insects cannot develop resistance to DE, though mortality often occurs within 24 to 72 hours after exposure.
Using Diatomaceous Earth Safely Around Honey Bees
The physical killing mechanism of Diatomaceous Earth means that any insect, including the honey bee, is susceptible to its effects upon direct contact. If a foraging bee lands on a surface dusted with the powder, the particles can adhere to its body hairs, potentially leading to cuticle damage and desiccation. Therefore, the safety of DE relies entirely on the precision and timing of its application to minimize exposure to non-target insects.
Targeted Application
A primary safety rule is to never apply the powder directly to the blossoms, flowers, or foliage of plants where bees are actively foraging. Instead, focus the application on the ground, around the base of plants, or in crevices where target pests, such as ants or slugs, are known to travel or hide. This limits the exposure to pests that crawl rather than fly.
Timing of Application
Application timing is a highly effective way to protect foraging bees. Honey bees are generally most active during the warmer daylight hours, so applying DE late in the evening or at dusk is advisable. This allows the powder to settle and be effective against nocturnal pests before the bees begin their foraging trips the following morning.
Wet Application Methods
To further reduce the risk of airborne dust drifting onto flowers, DE can be applied as a wet slurry or spray. It only becomes effective as an insecticide once the water has dried completely. This method helps to target specific areas and prevents the fine particles from becoming suspended in the air where bees might fly through them. If a bee contacts the powder, its fuzzy body hairs may offer some temporary protection, but the risk of death remains. Preventative application measures are the most reliable safety strategy.