Moles are subterranean insectivores, mammals perfectly adapted to life beneath the soil surface. Species like the eastern mole (Scalopus aquaticus) use powerful forelimbs and specialized claws to excavate extensive tunnel networks. Digging is their primary method of hunting, creating shelter, and establishing territory. Not all tunnels are constructed equally, with different purposes dictating how far beneath the surface they extend.
Shallow Foraging Tunnels Versus Deep Runs
The most frequently observed sign of a mole’s presence is the raised ridge of soil snaking across a yard, which marks the shallow foraging tunnel. These temporary pathways, often located only 1 to 10 inches beneath the surface, are active hunting grounds. A mole patrols these runs to intercept earthworms, insect larvae, and other invertebrates. The soil is simply pushed up to create the path, which is why these runs are visible and easily collapse.
In contrast, the mole establishes more permanent, deeper routes that serve as subterranean highways. These deep runs are typically found between 12 and 24 inches down, sometimes extending further in favorable soil conditions. They are structurally sounder due to increased soil compaction at that depth, making them suitable for repeated use. Unlike foraging tunnels, these main arteries are carefully constructed and remain hidden from view above ground.
The Central Den and Nest Chamber
The deepest structure in a mole’s network is the central den, a chamber that serves as the animal’s home base. This spherical or oval chamber is often situated below the frost line to ensure stable temperatures and protection from harsh weather. Connecting to the deep runs, the central den is typically constructed at depths ranging from 18 inches to over 3 feet below the surface.
Within this chamber, the mole constructs a nest using dried grasses and leaves, providing a safe location for sleeping and raising young. The mound of soil often seen directly above this chamber, known as a molehill, is the result of the mole excavating and pushing earth upward. The den’s depth and robust construction ensure it acts as a refuge from predators and environmental extremes.
Environmental Factors Affecting Tunnel Depth
The depth of any mole tunnel is not static; it fluctuates based on the surrounding environment and seasonal cycles. Soil composition plays a role, as moles find it easier to dig deeper in loose, sandy loam than in dense, compacted clay. The availability and movement of their invertebrate prey influence where a mole excavates its foraging tunnels.
During drought or freezing temperatures, the worms and grubs migrate deeper into the soil to seek moisture or avoid the cold. Consequently, moles follow their food source, temporarily deepening their foraging runs. The lower limit for all tunneling activity is determined by the water table, as moles cannot maintain tunnels that are constantly flooded.