Dozens of animal species dig holes in the ground, from tiny solitary bees that leave pencil-width openings in garden paths to gopher tortoises that excavate tunnels stretching several meters long. The answer to this question depends heavily on where the hole is, how big it is, what shape the surrounding soil takes, and what part of the world you live in. Mammals get most of the blame when mysterious holes appear in a yard, but reptiles, amphibians, birds, crustaceans, and a surprising variety of insects are equally prolific diggers.
Moles and Pocket Gophers
If you find raised ridges snaking across a lawn or fan-shaped mounds of loose soil with no visible entrance, the most likely culprits in North America are moles or pocket gophers. These are among the most specialized burrowing mammals on the planet, and they operate almost entirely underground.
Moles belong to the family Talpidae and are built for digging in a way that few other mammals can match. Their forelimbs have evolved for a style of excavation called humeral rotation digging, where the entire upper arm bone rotates to power broad, paddle-like front paws through soil. This approach is so distinctive that researchers studying mole bone structure have described it as unparalleled among other digging animals.1PubMed Central. Bone microstructure as an indicator of digging ability in moles (Talpidae, Eulipotyphla) Moles eat earthworms and grubs, so their tunnels tend to follow shallow, winding paths just below the surface. The classic sign of mole activity is a raised ridge of earth you can press down with your foot, rather than a visible hole.
Pocket gophers leave more obvious evidence. They push excavated soil out of their tunnels, creating crescent- or fan-shaped mounds with a plugged hole off to one side. Researchers who have mapped pocket gopher tunnel systems found that adult gophers build longer and more expansive burrow networks than juveniles, and that the overall length and area of their tunnels shrink when soil has a high clay content, since clay is harder to dig through.2Journal of Mammalogy. Effects of Species, Sex, Age, and Habitat on Geometry of Pocket Gopher Foraging Tunnels Interestingly, regardless of species or habitat, the basic branching geometry of pocket gopher burrows stays consistent, suggesting an underlying foraging strategy shared across the family.
Both moles and pocket gophers are solitary and territorial, so a single animal can be responsible for a surprisingly large amount of surface disruption. Telling them apart usually comes down to mound shape: moles leave symmetrical, volcano-like mounds, while pocket gopher mounds are lopsided crescents.
Badgers and Other Medium-Sized Mammal Diggers
When the holes in the ground are bigger, the list of suspects shifts. In North America, the American badger is one of the most powerful excavators in the animal kingdom. Badgers are built low and wide with massive front claws, and they dig primarily to hunt burrowing rodents. A study of badger hunting behavior found that excavating entire burrow systems was their most common technique, though they also plugged the exits of ground squirrel tunnels to trap prey inside, accounting for up to about a quarter of their hunting actions in some years.3Journal of Mammalogy. Hunting Techniques and Tool Use by North American Badgers Preying on Richardson’s Ground Squirrels
The holes badgers leave behind are substantial. They create large, fan-shaped mounds of displaced soil while digging out rodent burrows, and these mounds persist in the landscape long after the badger has moved on. Research in shrub-steppe ecosystems found that nearly all active and recently crusted badger mounds still had excavation holes present, while about a third of older, recovering mounds also retained visible openings.4Journal of Mammalogy. Mounds of the American Badger (Taxidea Taxus): Significant Features of North American Shrub-Steppe Ecosystems These mounds are large enough to be considered significant landscape features that alter local soil dynamics.
Other medium-sized mammals that dig conspicuous holes include groundhogs (woodchucks), foxes, armadillos, and various ground squirrels. Groundhog burrows often have a large main entrance with a mound of dirt and one or more hidden bolt holes nearby. Fox dens tend to be wider than they are tall, sometimes with multiple entrances. Armadillos, common in the southeastern United States, dig cone-shaped holes a few inches across while rooting for grubs, in addition to their larger sleeping burrows.
Tortoises and Burrowing Reptiles
Not all ground holes are made by mammals. The gopher tortoise, native to the southeastern United States, digs some of the most impressive burrows of any reptile. These tunnels can extend several meters underground and provide stable temperature and humidity year-round. The gopher tortoise is considered a keystone species precisely because of these burrows: more than 60 vertebrate species and over 300 invertebrate species have been documented using them.5Ichthyology & Herpetology. Gopher Tortoise (Gopherus polyphemus) Vertebrate Burrow Commensals within a Private, Working Forest Landscape Even abandoned tortoise burrows continue to attract other animals, as research has shown that the composition of vertebrate visitors does not differ between active and abandoned burrows, suggesting the physical structure itself provides resources like shelter and stable microclimate regardless of whether the tortoise is still using it.
Monitor lizards in Australia and parts of Asia also dig burrows, as do various skink species around the world. But perhaps the most charming reptilian diggers are rarely seen because they spend most of their lives underground.
Toads That Dig Themselves Underground
Spadefoot toads are amphibians equipped with hard, keratinized “spades” on their hind feet that let them dig backward into soil. They spend the dry months buried underground, emerging only after heavy rains to breed in temporary pools. Research on the western spadefoot in southern California found that these toads strongly prefer sandy or loamy soils with low clay content for burrowing, and they overwhelmingly chose sites covered in leaf litter over areas dominated by grass or shrub cover.6PubMed Central. Movement and habitat selection of the western spadefoot (Spea hammondii) in southern California A spadefoot encountering a site composed entirely of leaf litter had roughly a 94% probability of choosing to burrow there, compared with only about 30% for a grassy site.
Studies on the Iberian spadefoot toad in Europe have explored how burrowing depth changes in response to environmental stress. These toads dig deeper in dry sand than in damp sand, apparently seeking underground moisture, and they also adjust their depth in response to the scent of predators like wild boar.7Journal of Zoology. The roles of sex and morphology in burrowing depth of Iberian spadefoot toads in different biotic and abiotic environments The holes spadefoot toads leave are small and often invisible at the surface, since the toad backs in and the soil closes over it. You would rarely notice them unless you happened to see the toad in the act.
Birds That Live in Holes
Burrowing owls are among the most recognizable birds that nest underground, standing on long legs at the entrance to a ground hole with an almost comically stern expression. But here is the thing: burrowing owls rarely dig their own burrows. On the Canadian prairies, the primary excavators of the burrows that owls use for nesting are Richardson’s ground squirrels and badgers.8Canadian Journal of Zoology. Factors associated with nest- and roost-burrow selection by burrowing owls (Athene cunicularia) on the Canadian prairies The owls show a clear preference for badger-sized burrows with taller tunnel entrances and prominent soil mounds.
In areas where burrowing owls nest among prairie dog colonies, similar selectivity applies. Owls choose nest burrows with longer tunnels, more neighboring burrows nearby, and active prairie dog presence in the surrounding area.9The Journal of Wildlife Management. Multiscale Habitat Selection by Burrowing Owls in Black‐Tailed Prairie Dog Colonies This dependence on other animals’ holes makes burrowing owls vulnerable when those digging species decline. Other birds that nest in ground holes include kingfishers, which tunnel into riverbanks, and various species of puffins and shearwaters that dig nesting cavities into soft coastal soil.
Insects and Ground-Nesting Bees
Some of the most abundant and least recognized hole-makers are insects. If you notice small, pencil-width holes appearing in bare patches of garden soil or sandy paths, ground-nesting bees are a strong possibility. Roughly 70% of bee species worldwide nest in the ground rather than in hives. These bees excavate vertical or angled tunnels into soil, pushing up small mounds of excavated material called tumuli at the surface.10PubMed Central. Automated Detection and Monitoring of Ground-Nesting Bee Nests Using Drone Imagery and Deep Learning Each tiny mound represents one bee’s nest entrance.
Solitary bee species create simple, linear, unbranched tunnels that they use for a single season and then abandon, allowing the burrows to gradually decay and fill in.11Geoderma. Morphology and temporal evolution of ground-nesting bee burrows created by solitary and social species quantified through X-ray imaging Social ground-nesting species tend to build more complex, branching tunnel systems that persist longer. The sheer number of individual nests in an aggregation can be striking: thousands of tiny holes clustered in a small area of bare soil, each belonging to a single female bee provisioning her own brood cells underground.
Cicada killer wasps produce larger and more conspicuous holes. These hefty wasps dig burrows in well-drained soil, leaving a characteristic mound of excavated sand at the entrance with a shallow furrow leading away from the opening where the wasp pushed material to the edge of the tumulus.12Journal of Insect Science. Intra- and Interspecific Prey Theft in Cicada Killers (Hymenoptera: Apoidea: Sphecius) The burrow entrance is roughly the diameter of a finger, and the mound can be several inches high. Despite their intimidating size, cicada killers are not aggressive toward people and are simply provisioning their underground nests with paralyzed cicadas for their larvae to eat.
Antlion Pits
Not every hole in the ground is a burrow. Antlion larvae, the immature stage of a delicate winged insect, construct cone-shaped pitfall traps in dry, sandy soil. These pits function as prey-catching devices rather than shelters. The larva buries itself at the bottom of the cone and waits for ants or other small insects to stumble over the rim and slide down the steep walls.
The engineering behind these pits is more sophisticated than it looks. During construction, the antlion selectively lines the pit walls with fine sand particles. Larger grains, which have a lower angle of repose, tend to roll to the center and get flung out by the larva, leaving the walls coated in material that is especially slippery for walking insects.13Animal Behaviour. The biophysics of pit construction by antlion larvae (Myrmeleon, Neuroptera) The resulting surface is treacherous: prey that steps onto it triggers miniature avalanches that carry it toward the waiting jaws below.
Some antlion species build simple inverted cones, while others construct more geometrically complex traps. One species studied in detail builds a pit composed of two nested inverted cones, with a shallow outer cone near the surface and a steeper inner cone dug deeper into the substrate.14Journal of Experimental Biology. Fine sand particles enable antlions to build pitfall traps with advanced three-dimensional geometry Maintaining these traps is an ongoing process. Sand continuously accumulates at the center as prey struggles or as wind blows debris in, and the larva throws it back out to keep the slopes steep and close to the angle at which they will collapse under an insect’s weight.15PubMed Central. Sand-throwing behaviour in pit-building antlion larvae: insights from finite-element modelling
Crayfish Chimneys and Coastal Crab Burrows
If you spot mud chimneys, small turrets of rolled mud pellets stacked a few inches high, rising from wet ground near ditches, streams, or low-lying yards, burrowing crayfish are the architects. Several crayfish species dig deep burrows to reach the water table, and the structure of the burrow depends on how deep the groundwater sits.16Animal Behaviour. Burrowing behaviour in the crayfish, Cambarus diogenes diogenes girard Some species build elaborate, branching burrow systems topped with prominent chimneys made from pellets of excavated mud.17Journal of Crustacean Biology. Evaluation of a Crayfish Burrowing Chamber Design with Simulated Groundwater Flow These chimneys can appear far from any visible water source, which often surprises people who associate crayfish strictly with streams and ponds.
On sandy ocean beaches, ghost crabs dig some of the most visible burrows around. These semi-permanent holes dot the upper beach zone, and their size and placement are governed by the physical properties of wet sand. Ghost crabs build where the sand is moist enough for grain cohesion to prevent tunnel collapse, and they keep tunnel diameters small enough to avoid structural failure.18PubMed Central. Physical constraints on sand crab burrows: Mechanical properties of wet sand explain the size and spatial distributions of burrows on beaches Ghost crab burrow density is used by ecologists as a tool for assessing beach health, since the crabs are sensitive to human disturbance like foot traffic and vehicle use.19Regional Studies in Marine Science. Burrow occupation rates and spatial distribution within habitat of the ghost crab Ocypode quadrata (Fabricius, 1787): Implications for impact assessments
Why Ground Holes Matter for Entire Ecosystems
Animals that dig holes are often described as ecosystem engineers because their excavation reshapes the landscape in ways that benefit many other species. Research in Tasmanian woodland found that the pits left behind by digging mammals acted as traps for organic matter and moisture. Soil inside foraging pits had higher fertility and water content and was significantly softer than undisturbed ground nearby, and these effects were strongest in habitats where the soil was naturally dry and nutrient-poor.20PubMed Central. Ecosystem engineering by digging mammals: effects on soil fertility and condition in Tasmanian temperate woodland In other words, digging animals create micro-sites that concentrate resources in otherwise harsh environments.
The gopher tortoise burrows mentioned earlier illustrate a different dimension of this effect: they provide physical refuge. Hundreds of species shelter in tortoise burrows, from indigo snakes and gopher frogs to various invertebrates. When the animal that digs the burrow disappears from a landscape, the cascade of consequences can be severe. A study on meerkats in arid environments found that meerkats cannot excavate their own sleeping and breeding burrows and depend entirely on holes abandoned by other species. If the distribution or abundance of those burrow-building species changes, meerkats and other secondary users face real survival and reproductive costs.21bioRxiv. The bind of the burrow: space use is dominated by selection for burrow habitat over foraging habitat in an arid-adapted carnivore
How to Tell What Made the Hole
When you find a mysterious hole in your yard or on a hike, a few features help narrow down the suspect list. Size is the most obvious clue. Holes under a centimeter wide in bare or sandy soil are usually insects: solitary bees, wasps, or beetles. Holes a couple of centimeters across with loose soil mounds point toward small rodents, moles, or chipmunks. Fist-sized or larger holes with significant excavated soil suggest something bigger like a groundhog, badger, fox, or tortoise.
Shape of the displaced soil matters too. Crescent-shaped mounds usually mean pocket gopher. Symmetrical, conical mounds suggest a mole. Fan-shaped mounds of large volume point to badgers. Mud chimneys in wet ground mean burrowing crayfish. A characteristic furrow leading away from a finger-width hole in sandy soil is a telltale sign of a cicada killer wasp. Perfectly conical pits in dry sand, a few centimeters across with no mound, are antlion traps.
Location provides context. Holes near water or in saturated ground suggest crayfish or muskrats. Holes on sandy beaches are ghost crabs. Holes in open grassland near prairie dog towns might belong to burrowing owls. And clusters of tiny holes appearing in a sunny patch of compacted soil in spring often belong to ground-nesting bees that will be gone in a few weeks.
The Deep History of Burrowing
Burrowing is ancient. Some of the earliest trace fossils from over 500 million years ago, around the Ediacaran-Cambrian transition, were once interpreted as burrows made by worm-like organisms tunneling through seafloor sediment. These markings in stone were taken as evidence that animals first began actively moving through and disrupting the ground during this period. However, researchers have questioned whether all of these early traces really were burrows in the traditional sense, or whether some might have been external molds created by organisms that displaced sediment through growth rather than active digging.22PubMed Central. Were the First Trace Fossils Really Burrows or Could They Have Been Made by Sediment-Displacive Chemosymbiotic Organisms? The debate matters because if the earliest “burrows” were not actually dug, the timeline for when animals first began actively engineering their environment shifts forward.
Regardless of when it first appeared, burrowing has evolved independently in virtually every major animal group: mammals, reptiles, amphibians, birds, insects, crustaceans, arachnids, and worms. The strategy solves a remarkably consistent set of problems across all of these lineages: temperature regulation, predator avoidance, moisture conservation, and access to underground food. That convergence is part of why so many different animals produce holes that, at a glance, look confusingly similar. A hole is a hole, but the animal behind it could be almost anything.