Diatomaceous Earth (DE) is often sought as a natural pest control solution when ground bees appear on a lawn. The sudden appearance of small, volcano-like dirt mounds signals the presence of these insects, prompting a search for an immediate management method. Understanding how this naturally occurring substance interacts with the unique biology and behavior of ground bees is necessary to evaluate its effectiveness as a control option.
Understanding Ground Bees
The bees commonly found nesting in the ground are typically solitary species such as mining bees (Andrena), cellophane bees (Colletes), or sweat bees (Halictids). These insects are not colony dwellers like honey bees or yellow jackets, but rather individual females that dig their own nests, sometimes in large, aggregated groups in a small area. The nests appear as small, often temporary, dirt mounds with a single, pencil-sized hole at the center, typically found in areas with sparse vegetation, loose soil, or poor drainage.
These bees are non-aggressive and rarely sting unless they are stepped on or trapped, as they do not have a hive to defend. Ground bees are important native pollinators, often emerging early in the spring to pollinate fruit trees and other early-blooming plants. Their activity is generally short-lived, lasting only about three to six weeks before the new generation of larvae develops underground for the rest of the year.
How Diatomaceous Earth Works
Diatomaceous Earth (DE), specifically the food-grade variety, is a naturally occurring powder made from the fossilized remains of ancient, single-celled algae called diatoms. These fossils are composed primarily of silica and have rigid, microscopic skeletons. When processed into a fine powder, the particles possess sharp, jagged edges that are harmless to humans and pets but harmful to insects.
The substance kills insects through a mechanical process, meaning pests cannot develop resistance to it. When an insect crawls across the powder, the sharp edges scratch and damage the protective, waxy outer layer (the cuticle) of the exoskeleton. This damage allows the insect’s internal moisture to escape rapidly, a process known as fatal desiccation. The powder also absorbs lipids and moisture, accelerating dehydration until the insect dies.
Effectiveness Against Ground Bees
Diatomaceous Earth is effective in killing any insect, including a bee, that comes into direct, sustained contact with the dry powder. However, its practical effectiveness against ground bees is often limited by environmental conditions and the insects’ behavior. The fundamental challenge is that DE loses its abrasive and desiccating properties when it becomes wet or damp, which is common in outdoor soil environments.
Ground bees spend most of their time inside their underground nests, only encountering the powder when entering or exiting the burrow. For the powder to be effective, it must be applied in a dry, thin layer directly in their path and remain completely dry. If the soil around the nest entrance is moist from dew, rain, or irrigation, the DE will quickly clump and become inert. The non-selective nature of the product also means that any beneficial insect will be harmed if they crawl through the treated area.
Safe Application and Alternatives
To minimize risk to other foraging pollinators, food-grade DE should be applied directly around the nest entrance. Application should be performed late in the evening or very early in the morning when the bees are dormant inside their nests. It is important to wear a mask during application to avoid inhaling the fine silica dust, as mineral dust can cause respiratory irritation.
Because ground bees are beneficial and their nesting season is temporary, non-lethal management strategies are preferred. Ground bees favor dry, bare, or sandy soil for nesting, so changing the soil conditions is the most effective deterrent. Applying a thick layer of mulch or compost over the affected area can discourage nesting by physically blocking access to the soil.
A simple and effective method is to increase irrigation in the area. Ground bees avoid wet soil, and regularly watering the section of lawn where the nests are located will encourage the bees to relocate to a drier site. Maintaining a thick, dense turf or groundcover will also eliminate the bare patches of soil these bees seek out. Recognizing the short duration of the nesting period allows for temporary tolerance, which preserves these valuable pollinators.