Ants in a lawn can be both beneficial and detrimental to the health and appearance of turfgrass. Their impact depends on the ant species, the size of the colony, and the overall health of the grass. Understanding these nuances is important for deciding whether intervention is necessary.
Physical Damage Caused by Nesting
The most visible harm ants inflict on a lawn comes from their excavation activities near the surface. This results in the formation of small piles of soil, commonly known as ant mounds or anthills. These mounds primarily cause mechanical damage to the lawn rather than biological harm.
When mounds are numerous or large, they can smother the underlying turfgrass, blocking sunlight and creating noticeable bare spots or patches of dead grass. This soil displacement also destabilizes the lawn’s surface, making it uneven and bumpy, which can interfere with routine maintenance like mowing. Running a lawnmower over these hard-packed mounds can dull the blade and scatter the soil, creating a messy appearance.
While a single mound may seem insignificant, a high density of colonies can collectively lead to a significant reduction in turf quality. The damage is largely aesthetic and mechanical, but in severe cases, the soil removal can expose and damage the shallow roots of the grass, causing yellowing and die-off in the immediate vicinity of the nest.
Unseen Benefits for Soil Structure
Despite the surface disruption, ants also play a positive ecological role that promotes the long-term health of the soil beneath the lawn. Their extensive tunneling activities function as a natural form of soil aeration, similar to the work done by earthworms.
As they excavate their complex underground networks, ants loosen compacted soil, which allows for better air circulation, water infiltration, and root penetration. This improved soil structure helps grass roots access oxygen and water more effectively. Furthermore, ants contribute to nutrient cycling by acting as scavengers, breaking down organic debris, dead insects, and decaying plant matter.
This organic material is often incorporated into their nests, enriching the soil with nutrients, including nitrogen, as it decomposes. Their activities promote overall soil fertility and structure.
Indirect Harm Through Pest Management
A less obvious, but potentially more damaging, consequence of ant presence involves their symbiotic relationship with other garden pests. Certain ant species actively “farm” sap-sucking insects, such as aphids, scale, or mealybugs.
Ants protect these pests from natural predators like ladybugs and parasitic wasps in exchange for a sugary waste product called honeydew, which the pests excrete after feeding on plant sap. This protection allows the sap-suckers to thrive unchecked, leading to increased populations that damage the grass and nearby ornamental plants.
The aphids themselves are the direct cause of the plant damage, as they drain the plant’s resources and can transmit plant viruses. The ants’ behavior essentially prevents natural biological controls from regulating the pest population, creating an environment where destructive insects can flourish.
Deciding When and How to Manage Populations
Intervention is generally warranted when the physical damage from mounds becomes excessive, when aggressive or stinging species are present, or when ant activity is clearly linked to an outbreak of sap-sucking pests. Since ants offer benefits to the soil, a targeted approach is preferable to broad-spectrum chemical treatments, which can harm the entire lawn ecosystem.
Mowing the grass at a higher setting (typically 3 to 4 inches) and leaving the clippings helps create an environment that ants find less attractive for nesting. For surface mounds, simply brushing or raking the soil flat when dry can mitigate aesthetic and mechanical issues, preventing mower damage and allowing the grass to recover. Spot treatments or simple displacement methods should be the first resort for persistent colonies, such as pouring a solution of soapy water directly onto the nest.