Mole rats are rodents adapted for a subterranean existence, spending nearly their entire lives underground. These animals have evolved a specialized set of behaviors and physical traits that allow them to construct and inhabit extensive burrow systems. Their constant digging carves out a complex world hidden from view.
The Digging Mechanism
The primary tool for a mole rat’s excavation is its large, ever-growing incisor teeth. These teeth are positioned outside the mouth, a feature that allows the animal to dig without getting soil in its mouth. The lips seal tightly behind the incisors, forming a barrier against dirt and debris. This dental adaptation is supported by powerful jaw muscles, with about a quarter of the animal’s total musculature dedicated to closing the jaws for digging.
While the teeth do the heavy work of breaking up the soil, the mole rat’s limbs play a secondary but important role. The forelimbs are used to scrape and gather the soil loosened by the teeth. Then, using their hind feet, which have hairs between the toes that act like a broom, they kick the accumulated earth backward through the tunnel.
A kinematic analysis of their digging reveals a specific sequence of movements. The process begins with the animal anchoring its upper incisors into the soil. With the upper teeth held stationary, the lower incisors are then elevated, scooping soil upward. This is followed by a quick, downward rotation of the head, which dislodges the soil and drops it beneath the head, ready to be kicked away.
The Purpose of Tunnels
The tunneling of mole rats is driven by the need to find food, creating extensive foraging networks. Mole rats are herbivores, feeding on the underground parts of plants like roots, bulbs, and tubers. Since they do not travel above ground, burrowing is the only method they have to locate these food sources, which are often patchily distributed.
The burrow system includes distinct chambers used for different activities. Deep within the network are nesting chambers, often lined with soft plant material, where the colony raises its young. Other designated areas serve as toilets, helping to keep the main living quarters clean.
The tunnels themselves also serve various functions based on their depth. Superficial tunnels are often used for foraging and can help with thermoregulation, as the animals can move into warmer, sun-heated shallow areas. Deeper tunnels provide access to larger food sources and connect to the main living chambers, offering protection from predators and environmental extremes.
Cooperative Tunneling and Burrow Systems
In species like the naked mole-rat, the construction of vast underground networks is a social effort where individuals work together in an organized fashion to excavate new tunnels. This process resembles a “chain gang,” where one mole rat works at the front, digging with its teeth, while a line of workers behind it passes the loosened soil back. The last mole rat in the chain kicks the soil out of a surface opening, often creating small, volcano-like mounds.
This cooperative digging allows colonies to create immense and complex burrow systems that can span several kilometers in total length. A single colony’s tunnel network can cover a large area, connecting its various specialized chambers.
Different members of the colony may have different roles in the tunneling process. While some individuals specialize in digging at the tunnel face, others are responsible for transporting the excavated soil or defending the colony. This division of labor, particularly in eusocial species like the naked mole-rat, allows for the continuous and efficient expansion of their underground world.