Animals create a variety of subterranean structures, from simple scrapes to intricate tunnel systems. These excavated spaces serve numerous purposes, highlighting how animals adapt their surroundings to meet their fundamental needs. The forms these underground dwellings take are as varied as the creatures that construct them, reflecting specialized adaptations for life beneath the surface.
The Reasons Animals Dig
Animals dig for essential biological and behavioral reasons, primarily centered on survival and reproduction. One motivation is the need for shelter and protection from various environmental threats. Burrows offer refuge from harsh weather conditions, including extreme heat, cold, and heavy precipitation, maintaining a more stable microclimate underground. They also provide a secure hiding place from predators, allowing animals to escape detection and evade capture.
Beyond immediate safety, excavated spaces are crucial for resource management and reproduction. Many species use holes for food storage, caching provisions to ensure a supply during times of scarcity. These subterranean larders keep food safe from scavenging by other animals. Burrows also serve as nurseries, offering a safe and stable environment for raising young away from external dangers.
Digging is also integral to an animal’s ability to hunt and forage. Some predators create tunnels to ambush prey, while herbivores dig to access underground roots, tubers, or insects. For some, burrows function as escape routes, providing a quick retreat when danger approaches.
Architects of the Underground: Common Mammals
Many common mammals are skilled excavators, each leaving distinct signs of their underground activities.
Groundhogs, also known as woodchucks, construct extensive burrow systems. These are often identified by a large main entrance, 10 to 12 inches in diameter, featuring a significant fan-shaped mound of excavated dirt. Their burrows can extend up to five feet deep and 15 to 25 feet horizontally, often including multiple secondary escape holes.
Moles create two primary types of tunnels: surface runways and deeper main burrows. Surface runways appear as raised, often grassless streaks just beneath the lawn’s surface, used for foraging. The deeper tunnels, up to 70 centimeters deep, are marked by volcano-shaped molehills formed from soil pushed to the surface through vertical shafts. These tunnel systems serve as a trap for invertebrates, their primary food source.
Pocket gophers are known for their crescent-shaped or horseshoe-like mounds of loose dirt, with the entrance hole typically off to one side and plugged with soil. Their burrow systems are intricate, featuring main tunnels less than two feet deep, lateral foraging tunnels, and deeper chambers up to six feet underground for nesting and food storage.
Badgers construct large, elaborate den systems called setts, which are extensive networks of tunnels and chambers. Sett entrances are often D-shaped, wider than they are tall, reflecting the badger’s stocky build. These entrances are typically accompanied by substantial piles of excavated soil, especially in well-established setts that can have dozens of openings and extend for hundreds of meters underground. The soil around active sett entrances may appear smooth or “polished” from frequent use.
Foxes also dig dens, often found in secluded areas such as dense thickets, under tree roots, or on hillsides. Fox dens may have multiple entrances, sometimes five or more, providing various escape routes. The presence of odors or scattered prey remains can indicate an active fox den. Foxes may even temporarily use abandoned badger setts.
Rabbits create burrows, often referred to as warrens, which are interconnected underground chambers. A main entrance is typically surrounded by a mound of dirt, though additional, less noticeable entrances may also exist. These burrows can reach depths of nearly 10 feet and span up to 150 feet horizontally, housing multiple rabbits within their communal living spaces.
Voles, small rodents, dig a network of small, pencil-sized holes, typically one to two inches in diameter. These holes are often found in grassy areas or under dense vegetation, leading to shallow surface runways that voles use to travel and forage. Unlike many other burrowing mammals, voles do not create large, conspicuous mounds of soil at their burrow entrances.
Beyond Mammals: Other Digging Creatures
The practice of creating holes extends beyond mammals to a diverse array of other animal groups, each employing unique methods.
Reptiles, for example, include skilled burrowers such as certain snakes and tortoises. Hognose snakes, known for their upturned, shovel-like snouts, burrow headfirst into sandy soil to regulate body temperature, hide from predators, and hunt prey like toads. Gopher tortoises excavate distinctive burrows in well-drained, sandy soils; their burrow entrances are typically half-moon shaped, with a flat bottom and high dome, and are often accompanied by a mound of loose sand called an “apron”. These burrows can shelter over 360 other species.
Amphibians also utilize the ground for shelter. Some frogs and toads can burrow into soft soil, particularly during dry or cold periods, a behavior known as aestivation. This allows them to escape unfavorable surface conditions and conserve moisture. They typically use their hind legs to dig backwards into the substrate.
Insects demonstrate burrowing capabilities, creating structures that range from simple to highly complex. Cicada nymphs emerge from the ground, leaving behind distinct, circular exit holes after spending years developing underground. Ants construct subterranean colonies with networks of tunnels and chambers, marked by small entrance holes, often surrounded by a mound of excavated soil known as an anthill. Various ground-nesting wasps and bees also dig individual or communal burrows in the soil for their nests, often with a single entry point leading to a chamber where they lay eggs and store provisions.
Spiders also create ground holes. Trapdoor spiders are notable for building silk-lined burrows that are capped with a camouflaged, hinged lid made of soil and vegetation. These spiders use their burrows as ambush points, waiting just inside the trapdoor to detect vibrations of passing prey before rapidly emerging to capture them. Their burrows can be up to 30 to 40 centimeters deep and are expertly disguised to blend with the surrounding environment.