Moles are subterranean mammals known for their digging capabilities and their life spent almost entirely underground. They create intricate tunnel networks that serve multiple purposes. These animals, though small, significantly influence their environment through their constant excavation.
Adaptations for Efficient Digging
Moles possess physical adaptations for efficient digging. Their forelimbs are large, broad, spade-like, and have powerful claws. Rotated outward from the body, these forelimbs resemble oars, allowing them to push soil aside with force. An extra bone in their wrist, sometimes called a “false thumb” (os falciforme), widens their digging surface for shoveling.
Strong shoulder muscles power these forelimbs, generating lateral force about 30 times their body weight. Their body shape is cylindrical and streamlined, reducing friction as they move through soil. Additionally, their short, velvety fur can lie in any direction, preventing soil from getting trapped and allowing them to move both forward and backward within their narrow tunnels with ease. These combined features contribute to their remarkable ability to excavate and navigate their underground habitat.
Factors Influencing Digging Speed
The speed at which moles dig varies depending on several factors. Moles can excavate new tunnels at 12 to 18 feet per hour. In optimal conditions, such as soft, moist, and crumbly soil, they can dig even faster, potentially reaching up to 20 feet per hour. This allows them to create tunnel systems extending up to 150 feet daily.
Soil type is a primary determinant of digging speed; moles prefer loose, well-drained soils rich in organic matter. Conversely, compacted clay soils or dry conditions make digging more challenging and can slow them down. Different mole species may also exhibit varying digging efficiencies based on physical characteristics. The purpose of the digging influences speed; exploratory tunnels, often shallower, might be created more quickly than deeper, more permanent main burrows. Younger, more vigorous moles can expand their tunnel networks more rapidly than older ones.
The Purpose of Mole Tunnels
Mole tunnels serve multiple functions for survival. A primary purpose is foraging for food, as moles are insectivores with a high metabolism, consuming a significant portion of their body weight daily in earthworms, grubs, and other insects. Their tunnel systems act as traps, allowing them to collect invertebrates that fall in.
Beyond food, tunnels provide shelter from predators and a stable environment for raising young. Deeper tunnels, often 6 to 12 inches underground, serve as living spaces, nesting chambers, and food storage. Shallow surface tunnels are primarily for hunting and appear as raised ridges. Moles also use tunnels for thermoregulation, moving deeper underground in cold or dry weather to follow food and escape extreme temperatures. These networks are central to their solitary lifestyle.