Diatomaceous earth (DE) is a popular substance used in gardens and homes as a non-toxic pest control method. It is composed of the fossilized remains of tiny aquatic organisms called diatoms, which are rich in silica. This fine powder controls pests through a physical mechanism rather than a chemical one, offering an alternative to synthetic insecticides. This physical action raises concerns about its impact on beneficial insects, particularly butterflies, which are important for pollination. Understanding how DE affects the delicate life stages of butterflies is necessary for responsible use.
How Diatomaceous Earth Kills Insects
Diatomaceous earth functions as an insecticide due to the microscopic structure of its silica particles. These particles appear as sharp, jagged shards of fossilized shells, and their abrasive nature is the primary mechanism for pest control against insects and other arthropods.
When an insect crawls over DE, the sharp edges scrape away the protective waxy layer, or cuticle, covering the insect’s exoskeleton. This coating is designed to prevent water loss. Once the cuticle is damaged, the porous DE absorbs the insect’s oils and fats. The combined effect of abrasion and absorption leads to rapid dehydration, a process known as desiccation. Insects cannot develop a resistance to this physical method, unlike many chemical pesticides.
The Direct Impact on Butterflies and Larvae
Diatomaceous earth kills butterflies because its physical mechanism does not differentiate between pest and beneficial insects. Any insect in direct contact with the fine powder is susceptible to desiccation. Vulnerability is substantially higher for the larval stage, the caterpillar.
Caterpillars are soft-bodied and slow-moving, spending time crawling across plant surfaces where DE is often applied. Their pliable skin is more easily damaged by the abrasive silica particles than the hardened exoskeletons of adult insects. Continuous contact with dusted surfaces ensures maximum exposure, leading to faster desiccation and a high mortality rate.
Adult butterflies, while possessing a more rigid exoskeleton, are also vulnerable if they land in or crawl through the dust. The powder can damage the delicate membranes of their wings or abrade their legs, impairing their ability to fly and feed. Because the physical action of DE is non-selective, direct application to flowers or feeding areas can harm visiting adult pollinators. The threat is based entirely on physical contact with the dry powder.
Minimizing Risk to Beneficial Pollinators
Users can employ specific application strategies to limit the exposure of beneficial insects while still targeting pests.
Timing Application
One effective technique involves applying the powder only when pollinators are inactive. Butterflies and most other pollinators are active during the day. Applying DE at dusk or in the early evening ensures the powder targets nocturnal or crawling pests while butterflies are resting.
Targeted Placement
Targeted application is necessary; instead of broadly dusting plants, focus the powder only on the base of plants, the soil around the perimeter, or specific leaves where pests are observed. Avoiding application directly onto blossoms and open flowers protects adult butterflies and foraging bees.
Using a Slurry
Another method is to mix DE with water to create a slurry and spray it onto surfaces. While wet, the DE is ineffective, but once the water evaporates, it leaves behind a thin, effective layer of dust that is less likely to become airborne. This technique allows for more precise placement and reduces accidental contact with non-target insects flying nearby. Reapplication is necessary after rain or heavy dew, as moisture renders the DE temporarily ineffective until it dries again.