Pill bugs, also known as roly-polies, are common crustaceans found in damp areas of gardens, under mulch, or near foundations. While they primarily consume decaying matter, large populations can damage young seedlings and tender plant growth, becoming a nuisance for gardeners. Diatomaceous Earth (DE) is cited as an effective, non-chemical solution for managing these pests. This fine powder acts as a physical control agent, eliminating pill bugs upon contact.
The Mechanism: Why Diatomaceous Earth Kills Pill Bugs
Diatomaceous Earth is a naturally occurring, soft, siliceous sedimentary rock crumbled into a fine powder. This material is derived from the fossilized remains of microscopic, single-celled aquatic organisms called diatoms. Their skeletal remains are composed primarily of silica.
When viewed under a microscope, DE particles appear as jagged, razor-sharp fragments. For pill bugs, contact with this powder is fatal due to desiccation. The fine particles physically abrade the pill bug’s waxy, protective outer layer, known as the cuticle or exoskeleton.
This waxy layer prevents moisture loss, which is critical for a creature that needs high humidity to breathe through its gill-like structures. As the sharp DE fragments scratch through this barrier, the powder simultaneously works as an absorbent, drawing out oils and moisture from the pill bug’s body.
The combined mechanical damage and moisture absorption lead to rapid dehydration. This physical method of control means pill bugs cannot develop resistance to Diatomaceous Earth, unlike chemical pesticides. Effectiveness depends entirely on pests moving across the dry powder barrier.
Choosing the Right Diatomaceous Earth for Home Use
Selecting the right Diatomaceous Earth is important for safety, as two distinct grades exist. The only type recommended for use in the home, garden, or around pets is Food Grade Diatomaceous Earth, which is composed almost entirely of amorphous silica.
Food Grade DE contains a low concentration—typically less than two percent—of crystalline silica. This composition makes it safe for use where inhalation by humans or pets is possible. It is recognized for pest control and as an anti-caking agent in the food industry.
Conversely, Filter Grade, often marketed as Pool Grade DE, is unsuitable for pest control applications. This grade is thermally treated, or calcined, which changes its structure. The heat processing converts much of the amorphous silica into a high concentration of crystalline silica, sometimes reaching sixty percent.
Crystalline silica is toxic when inhaled and poses a serious respiratory hazard to mammals, including humans and pets. Always confirm the product label states “Food Grade” before purchasing.
Practical Application for Effective Control
For Diatomaceous Earth to work, the environment must be dry, as moisture renders the powder ineffective by causing it to clump. Begin by clearing away organic debris like mulch, leaf piles, or boards that provide damp hiding spots for the pill bugs. The goal is to create a dry, exposed surface.
A light, even dusting is more effective than applying a thick layer of powder. A bulb duster or a shaker container with a perforated lid allows for the application of a thin, visible film over the affected area. This fine layer ensures pill bugs readily contact the powder as they move.
Target the primary pathways and harborage sites. This includes dusting around the perimeter of garden beds, along concrete foundations, and under elevated structures like potted plants or steps where humidity is trapped. Applying a band of DE around the base of vulnerable plants creates a protective barrier the pests must cross.
Because water neutralizes the physical effect of the powder, reapplication is necessary after rainfall or heavy watering. Maintaining a continuous, dry barrier is the only way to ensure ongoing control. Regular inspection indicates when the powder has been disrupted and needs refreshing.