Moles are small, specialized insectivores that spend nearly their entire lives beneath the soil surface. Although rarely seen, the visible evidence of their constant activity is the characteristic mound of earth, commonly known as a molehill. Understanding the purpose of these mounds requires looking at the mole’s motivation for digging and the mechanics of soil disposal.
The Primary Purpose of Excavation
The mole’s life is defined by a continuous need to find food, making excavation an activity necessary for survival. Moles are high-energy animals that must consume a large amount of food daily, primarily consisting of earthworms and insect larvae. The extensive tunnel system they construct serves as a passive trap line, where invertebrates naturally fall into the passages and are later collected by the mole.
These tunnel networks are not random; they represent a permanent, defended territory providing constant access to prey. The mole must continually patrol and maintain this system, which can span hundreds of feet in length. Digging is also necessary to establish permanent living spaces, including deep resting chambers and nesting areas.
The constant need for food drives the mole to expand its network, especially when existing tunnels become unproductive or resources shift due to environmental changes. This perpetual movement of soil is therefore a direct result of the mole’s predatory lifestyle. The entire structure of the burrow system is focused on maximizing the capture of soil-dwelling invertebrates to meet the animal’s high metabolic demands.
How the Molehill is Constructed
Molehills are created specifically for disposing of excess soil excavated during the construction of deep tunnels or chambers. When the mole digs its main, deep tunnels, it dislodges a significant volume of earth. This displaced soil cannot be compressed into the tunnel walls, especially when tunnels are being expanded or a larger nesting chamber is being built.
To manage this spoil, the mole pushes the loose dirt up a vertical shaft, or ‘run,’ connecting the active tunnel to the surface. The mole uses its powerful, spade-like forepaws to shove the soil plug upward through this shaft. This action results in the characteristic conical or volcano-shaped mound of loose, fine soil at the surface, marking the exit point of the vertical run.
The mole may return to the same shaft multiple times to expel more soil as it continues its work below ground, adding to the size of the mound. Once the necessary soil has been expelled, the mole often plugs the vertical shaft from below. This soil disposal mechanism is separate from the tunnel creation itself and is solely for removing earth that cannot be compacted elsewhere.
Surface Ridges Versus Deep Tunnels
The visible signs of mole activity are not uniform; molehills represent only one type of subsurface construction. Molehills are associated with the excavation of deep, permanent tunnels and living quarters, which occur far below the root zone. The large volume of earth removed from these deeper structures necessitates expulsion to the surface.
In contrast, the raised lines or ridges seen across a lawn are created by shallow, temporary foraging tunnels. These tunnels are just beneath the grass roots, allowing the mole to hunt for prey close to the surface. In this shallow digging, the mole pushes the loosened soil upward against the turf, creating a raised, soft ridge rather than ejecting the dirt entirely.
These surface runs are quicker to construct and are used primarily for feeding. The deep tunnels that result in molehills are built for long-term habitation and connectivity within the territory. The presence of a molehill indicates that the mole is engaged in a major construction or repair project at a significant depth, while a surface ridge is a sign of active, shallow hunting.