A mole hill, or mole mound, is the most common visible evidence of a subterranean mammal’s activity beneath the surface of a lawn or field. These piles of excavated earth are the byproduct of a mole’s tireless digging, establishing a complex underground network. While often viewed as a nuisance that disrupts the aesthetic of a yard, the presence of a mole hill signifies a hidden world of complexity. Understanding the structure and purpose of these mounds offers insight into the life of the mole.
The Anatomy and Purpose of Mole Hills
A mole hill is characterized by its distinct, conical, or volcano-like shape, where displaced soil is pushed upward through a central vertical shaft. This mound is essentially a waste pile of fine, loose dirt removed from the mole’s deep, permanent tunnels. The size varies depending on the mole species and soil conditions, but it is typically a rounded heap with no visible entrance hole on its side.
The formation of the hill serves the mechanical purpose of clearing the main thoroughfares of the mole’s habitat, often located between 12 and 18 inches below the surface. A mole uses its broad, powerful front paws to loosen the soil, which is then pushed to the surface through an exit route that is immediately plugged from below. The hill also performs a secondary function by acting as a form of ventilation, helping to circulate air within the tunnel system. New mole hills generally increase in frequency in spring and autumn as moles expand their territories or as young moles disperse.
Distinguishing Mole Hills from Other Mounds
Correctly identifying a mole hill is important because other burrowing animals, such as gophers, create similar surface disturbances. A mole hill is typically symmetrical and circular with the opening plugged centrally, making it look like a miniature volcano. The soil found in the mound is often finely textured because it has been excavated from deeper layers of the ground.
Gopher mounds, in contrast, usually present a crescent, horseshoe, or fan shape, with the entrance hole plugged off-center. The difference in mound structure reflects the animal’s primary behavior: moles are insectivores tunneling to hunt earthworms and grubs, while gophers are rodents that tunnel primarily for foraging on plant roots. Moles use their mounds to dispose of excess soil from deep runs, whereas a gopher creates its mound by backfilling a lateral tunnel used to access the surface.
The Subterranean World Beneath the Hill
The mole hill is merely the exit point for the intricate tunnel system lying beneath the ground. Moles maintain two primary types of tunnels: deep main runs and shallow surface runs. The deep tunnels, which create the visible mole hills, are permanent, firm-walled highways used for travel and protection, often extending 12 to 18 inches or more below the ground.
These deep networks include specific chambers for nesting, raising young, and storing food, creating a self-contained underground city. Moles have a high metabolic rate, requiring them to constantly patrol their tunnels, which function as pit-fall traps for earthworms and other invertebrates. A single mole is an incredibly efficient excavator, capable of extending its tunnel system by as much as 150 feet in a single day under optimal conditions.
The shallow tunnels, known as surface runways, are temporary hunting galleries just beneath the turf and are indicated by raised ridges in the lawn, not conical hills. These temporary runs are used as the mole explores new feeding areas, following the movement of its prey. This constant digging helps aerate the soil and improves drainage, but the construction and maintenance of the deep, permanent system results in the characteristic mole hill.