Finding unexpected piles of dirt in your yard can be a frustrating mystery, disrupting the appearance of a manicured lawn. These mounds are visible evidence of activity occurring just beneath the surface. Subsurface animals, insects, or worms push soil to the surface as they excavate new tunnels, expand existing burrows, or deposit waste. Identifying the unique shape and composition of the dirt pile is the first step in understanding the creature responsible and deciding if action is necessary.
The Volcano Shape: Identifying Mole Hills
The most common source of large, raised soil deposits is the mole, an insectivore that spends nearly its entire life underground searching for food. Mole hills are distinctively symmetrical and conical, giving them a classic volcano-like appearance as the excavated soil is pushed straight up from below. The mole uses these mounds to clear soil from its main tunnel system, which can be 12 to 18 inches deep. These mounds typically lack a visible, open entrance hole because the mole plugs the opening from below. The soil within a mole hill is often coarser or chunkier, consisting of displaced subsoil. Moles also create shallow feeding tunnels just beneath the grass surface, which appear as raised, spongy ridges connecting the deeper mole hills. Their tunneling is a continuous process driven by high metabolic needs, as they hunt primarily for earthworms, grubs, and other soil invertebrates.
The Fan Shape: Identifying Gopher Mounds
A gopher mound presents a contrasting profile, offering a clear visual distinction from a mole hill. Gophers are rodents, and their mounds are generally asymmetrical, taking on a flatter, fan, or crescent shape. This shape is created because the gopher pushes excavated soil out of a lateral tunnel at an angle, depositing it to one side of the entrance. The defining characteristic is the presence of a distinct soil plug that seals the entrance hole, which is always offset to one side of the mound. This plug acts as a defense mechanism, keeping predators out and regulating humidity and temperature within their deeper burrow system. Gophers are herbivores, so their extensive tunnels are often located near plant roots, which serve as their primary food source.
Smaller Piles: Ant Nests and Earthworm Castings
Smaller deposits of soil on the lawn or garden often indicate the presence of insects or worms. Ant nests, commonly called anthills, are typically small, conical piles of fine, granular soil or sand. This material is the excavated debris from the ants digging their vertical and interlocking underground chambers. Earthworm castings are another small, common sight, often appearing as dark, wet, bumpy deposits on the soil surface. These small heaps are the excrement of certain earthworm species after they have digested organic matter and soil. While they can be a minor nuisance on fine turf, earthworm activity is beneficial because their castings are rich in nutrients and their tunneling aerates the soil.
Management and Removal Strategies
Effective management depends on correctly identifying the creature causing the disturbance, as the best solutions are species-specific.
Moles and Gophers
For moles, the most reliable control method is trapping within the active subsurface tunnels or main runways. Since moles are driven by their diet, reducing their food source by treating the lawn for grubs can help deter them, though this may not be a complete solution if earthworms are abundant. For gophers, trapping in the main runway is also the most effective removal strategy. Locating the main tunnel is accomplished by probing 8 to 12 inches away from the plugged side of a fresh mound. Exclusion is another method, involving burying galvanized hardware cloth or mesh at least two feet deep to create a physical barrier around vulnerable areas like garden beds.
Ants and Earthworms
Ant nests and earthworm castings require little intervention unless they are directly interfering with a structure or a specialized lawn. Ant nests can often be dispersed with a strong stream of water or minor localized treatments. Earthworm castings should be tolerated whenever possible, but they can be broken up and dispersed by raking the area when the deposits are dry.