A burrow is a hole or tunnel excavated into the ground by an animal, providing a space suitable for habitation or temporary refuge. This behavior is widespread across the animal kingdom, serving as a fundamental survival strategy in diverse environments. Animals create burrows for various purposes, from seeking shelter to raising their young, demonstrating a remarkable adaptation to their surroundings.
Animals That Dig
A wide array of animals across different classifications are known for their burrowing habits. Mammals are prominent burrowers, including small rodents like mice, voles, and chipmunks, which dig intricate tunnel systems. Larger mammals such as groundhogs, badgers, armadillos, and rabbits construct extensive burrows. The platypus, pangolins, and polar bears also create burrows, with polar bears digging maternity dens in snow or earth.
Reptiles also engage in burrowing, with many lizards, including skinks, horned lizards, and mole lizards, either digging their own tunnels or utilizing existing ones. Some snakes, like the Madagascar blind snake, spend most of their lives underground, while alligators are known to dig dens for refuge. Amphibians, such as various species of burrowing frogs and caecilians, possess muscular bodies and specialized heads to dig into soil.
The insect world is rich with burrowers, from social insects like ants and termites, which build complex underground colonies, to solitary bees and wasps that construct individual nests. Cicadas spend the majority of their lives as nymphs underground, and mole crickets are known for their subterranean tunnels. Even birds participate in burrowing, with species such as puffins, kingfishers, and burrowing owls creating nests in earthen tunnels or using burrows dug by other animals.
Why Animals Burrow
Animals construct burrows for a variety of functions that support their survival and reproduction. A primary reason is protection from predators, as burrows offer a physical barrier and a hidden retreat from threats above ground. This allows many species to quickly disappear underground when danger approaches.
Burrows also provide shelter from extreme weather conditions, including intense heat and biting cold. The ground acts as insulation, maintaining a more stable temperature underground compared to fluctuating surface temperatures. This thermoregulation helps animals conserve energy that would otherwise be spent coping with environmental extremes.
Another purpose of burrows is providing safe sites for raising young. Many species use burrows as nurseries, offering protection for vulnerable newborns from predators and harsh elements. Animals may also store food within their burrows, creating underground pantries to ensure a supply during periods of scarcity or hibernation. In some cases, burrows even serve as traps for prey, such as the conical pits created by antlions to capture unsuspecting insects.
How Burrows Are Built
The construction of burrows involves a range of specialized tools and techniques adapted to each animal’s anatomy and environment. Many burrowing mammals, such as moles, badgers, and armadillos, possess powerful forelimbs and strong, sharp claws specifically designed for excavating soil. These animals can rapidly dig, using their claws to break up the earth and their bodies to push or remove the loosened material.
Some reptiles and amphibians employ their heads or body structures for digging. Mole lizards and worm lizards use their tough, pointed heads to push through soil, while caecilians burrow with muscle contractions that move along their bodies. Insects like termites and some beetles chew through wood or soil to create their tunnels. Other animals, such as burrowing owls, do not always dig their own burrows but instead modify and occupy existing natural crevices or abandoned burrows made by other species like prairie dogs or tortoises.
The type of substrate influences how burrows are built. Animals adapt their digging methods to various materials, including loose, sandy soil, forest floors, and even harder substrates like wood or rock. For example, pocket gophers prefer loose soil for their extensive tunnel systems, while some sea urchins and clams can burrow directly into rock.
The Architecture of Burrows
Burrows exhibit a wide variety of structural complexities, ranging from simple tubes to elaborate multi-chambered networks. The design often reflects the specific needs and behaviors of the animal inhabiting it. Some burrows are relatively shallow, consisting of just enough space for temporary refuge or a simple hiding spot. Others can extend to great depths, reaching up to 30 feet, or stretch for hundreds of meters in total length.
Many complex burrows feature multiple entrances, which can provide escape routes from predators or aid in ventilation. Inside, burrows may contain various chambers, including dedicated areas for nesting, storing food, or sleeping. The network of tunnels connecting these chambers can be intricate, forming extensive systems, such as the warrens created by rabbits or the vast networks of great gerbils visible from satellite images. Although not always explicitly designed for ventilation, the multi-level and interconnected nature of these subterranean homes can contribute to maintaining a stable microclimate within the burrow.