Earthworms are segmented invertebrates often associated with healthy ecosystems, but their activity can create problems for managed landscapes. The primary reason people seek removal is the appearance of small, muddy mounds known as castings—piles of nutrient-rich excrement deposited on the surface. These castings disrupt the smooth finish of lawns, sports fields, or ornamental gardens. Reducing their presence often requires specific cultural adjustments and, in some cases, direct intervention.
Assessing the Necessity of Removal
Before implementing any removal strategy, it is important to understand the significant ecological role earthworms play in soil health. Earthworms are often described as “ecosystem engineers” because their burrowing activities physically alter the soil structure, which benefits plants and other organisms. These underground tunnels create channels that dramatically improve soil aeration, water infiltration, and drainage.
Earthworms also accelerate nutrient cycling by consuming and digesting organic material, such as dead roots and surface thatch. Their castings are significantly richer in available nutrients like nitrogen and phosphorus than the surrounding soil, effectively acting as a natural fertilizer. However, this beneficial activity becomes problematic when high populations of surface-casting species, such as the common nightcrawler, disrupt closely mowed areas. The resulting bumpy surface can interfere with ball play, cause mowing equipment to scalp the turf, or ruin the aesthetic of a high-value lawn.
Cultural and Environmental Control Strategies
Targeting the environment to make it less hospitable is the most sustainable long-term method for reducing earthworm populations. Earthworms prefer soils that are moist, rich in organic matter, and near-neutral in acidity; altering these conditions discourages their presence. One cultural strategy is modifying the soil’s pH level, as earthworm activity decreases significantly below a pH of 6.0. Applying acidifying agents like ammonium sulfate or iron sulfate can shift the pH to a less favorable range.
Reducing surface food sources is also effective, since casting species feed on organic debris like grass clippings and surface thatch. Collect grass clippings instead of leaving them, and regularly dethatch or aerate the turf to break down excessive organic matter. Proper water management influences worm activity, as earthworms stay closer to the surface when the soil is excessively moist. Implementing deeper, less frequent irrigation cycles encourages worms to burrow deeper, reducing surface casts.
In professional turf management, applying coarse sand topdressing can serve as a physical deterrent. The abrasive sand particles irritate the earthworm’s skin, making the top layer of soil less comfortable and potentially reducing casting activity.
Direct Removal and Chemical Options
Physical Expulsion Methods
For immediate or targeted reduction, active removal measures are available, though they must be used with caution. Physical expulsion uses irritant solutions to force the worms out of their burrows for surface collection. A common, less toxic method involves drenching the affected area with a solution containing saponins, natural compounds found in products like crushed tea seed pellets.
Saponins act as a surfactant that irritates the earthworm’s mucous membranes, causing them to quickly emerge. A single application of saponin-based products can expel a high percentage of worms and suppress casting for several weeks. Diluted mustard powder solution is another non-lethal expellant, though its effectiveness varies based on concentration and soil conditions.
Chemical Control Limitations
Chemical control options are highly regulated. No pesticide is currently registered by the U.S. Environmental Protection Agency (EPA) specifically for earthworm control in residential settings.
Some insecticides and fungicides, such as carbaryl, thiophanate-methyl, or imidacloprid, are toxic to earthworms as a side effect when targeting other pests. However, their application is rarely legal solely for worm removal. Regulatory bodies, such as those in the UK, have revoked the use of certain chemicals, recognizing earthworms as beneficial species.
Using any chemical product inconsistently with its label is illegal and poses risks to wildlife, the environment, and human health. Therefore, cultural controls remain the safest and most recommended approach.