Finding unexpected piles of soil can be a source of frustration for any homeowner. These mounds of dirt are a visible sign of subsurface activity. The material excavated is typically the result of an animal or insect tunneling for feeding, nesting, or simply moving through the soil. Understanding the source of the debris is the first step toward effective management. This guide will help you identify the creature responsible for the disruption.
Identifying Key Characteristics of Mounds
Identifying the source begins with a careful observation of the mound’s physical features. Homeowners should first examine the overall shape and symmetry of the soil pile. Is the mound a neat, uniform cone, or does it present as a more asymmetrical, fan-shaped deposit?
The texture of the excavated soil provides another important clue. Fine, granular soil suggests a different type of activity than clumpy, moist dirt or small pellets of mud.
A third factor is the location and presence of an entrance hole. Some mounds feature a visible opening directly at the center, resembling a miniature volcano. Other times, the entrance is completely plugged with soil and situated off to the side or buried beneath the center of the pile.
The final piece of evidence is the size of any visible tunnel opening. A larger, wider opening indicates a different type of animal than a tiny, pinhole-sized entry point. Analyzing these characteristics provides the necessary framework for accurate identification.
Mounds Created by Subterranean Mammals
The most common sources of large dirt mounds are subterranean mammals, primarily moles and gophers. Distinguishing between the two requires a close look at the mound’s structure. Moles create what are typically described as “volcano” mounds.
These molehills are generally symmetrical and conical, with the soil finely sifted and uniform in texture. The mole pushes soil up from below as it excavates its feeding tunnels, which are shallow runways used to hunt invertebrates like earthworms and grubs. The main entrance is usually centrally located beneath the mound and completely plugged with soil.
In contrast, gophers produce mounds that are distinctly fan-shaped or horseshoe-shaped. The soil they excavate is often coarser and less uniform than mole soil. This asymmetry is created because the gopher pushes the dirt out of a lateral tunnel opening as it maintains its extensive burrow network.
The main difference lies in the entrance hole, which is always located off to one side of the mound rather than centrally. This side entrance is perpetually plugged with soil, creating the characteristic “plugged crescent” shape. Gophers are herbivores that feed on plant roots and bulbs, making their activity potentially more damaging to garden plants than the mole’s insectivorous tunneling. Observing the difference in mound shape and entrance location is the most reliable way to differentiate between these two common yard inhabitants.
Mounds Created by Insects and Other Invertebrates
Smaller mounds are often the work of insects and other invertebrates. Ant mounds are perhaps the most recognizable of these, consisting of fine, granular soil piled up around a central opening. The size of these hills can vary dramatically, ranging from small piles created by pavement ants to large, complex structures built by species such as fire ants.
The soil in ant mounds is often extremely fine because the ants meticulously carry and deposit individual grains. The visible central opening serves as the primary entrance to their subterranean colony network. While not typically a threat to lawn health, certain species can pose a sting hazard to people or pets.
Another common sight, particularly after rain, are earthworm castings. These are small, messy clumps of excreted soil, which look like miniature coils of dirt left on the surface. These castings are a sign of beneficial activity, as earthworms improve soil aeration and nutrient cycling.
A final type of invertebrate mound is the crayfish “chimney,” found in damp, low-lying, or poorly drained areas. These structures are built from small pellets of mud stacked into a tower. The crayfish digs downward to maintain access to the water table, pushing the excavated mud up and around the opening to form the chimney.
Crayfish chimneys are an indication of persistent subsurface moisture. They are easily identified by their distinct tower shape and the pelletized construction material. Identifying these smaller mounds can help homeowners rule out more severe issues caused by mammals.
Initial Steps for Managing Yard Mounds
Once the source of the mounds has been identified, initial management steps can begin with observation and habitat modification. The first step is to confirm the activity is current by flattening a few of the mounds. If the mounds reappear within 24 to 48 hours, the creature is actively working in that location.
A highly effective initial strategy is modifying the habitat to make the area less appealing. Improving drainage will deter crayfish from building their chimneys and may discourage rodents seeking damp soil. For moles, reducing their primary food source is a non-lethal management option. This involves controlling soil invertebrates, such as white grubs and beetle larvae, which make up a significant portion of the mole’s diet.
Habitat modification also extends to removing potential attractants, such as excess ground cover or heavy layers of mulch near foundations, which can draw in insects and other small burrowing animals. Maintaining a healthy, dense turf can also discourage certain types of tunneling activity near the surface.
For subterranean mammals, homeowners can attempt non-lethal deterrents, such as low-vibration devices placed in the ground. These devices emit subtle sonic pulses that some animals find disruptive, encouraging them to relocate their burrowing activity elsewhere. Physical barriers, like burying hardware cloth vertically around small planting beds, can also provide a targeted defense against burrowing activity near valued plants.