Many frog species do burrow, and the behavior is far more common and varied than most people realize. More than 95% of burrowing frogs dig hind feet first into the soil, a method unique among land vertebrates, while a small minority go headfirst using specially shaped skulls and powerful forelimbs.1PubMed. Burrowing in frogs Frogs burrow for reasons ranging from surviving scorching deserts to amplifying their mating calls, and the underground lifestyle has driven some of the most dramatic body modifications found anywhere in the amphibian world.
How Frogs Dig
The overwhelming majority of burrowing frogs back into the ground rear end first. They use their hind legs in alternating, scooping motions to push soil aside, gradually sinking below the surface. This works because frog hind limbs are already positioned toward the back and sides of the body, and the muscles that power jumping double as effective digging tools. Some species have a hardened, spade-like bump on the inner edge of the hind foot called a metatarsal tubercle, which functions essentially like a built-in shovel blade. In dedicated burrowers like the Asian painted burrowing frog (Glyphoglossus molossus), the hind limb has additional modifications that angle the spade for maximum soil displacement and boost the force of the lower leg during digging.1PubMed. Burrowing in frogs
A handful of species take the opposite approach and burrow headfirst. The shovel-nosed frogs of Africa (genus Hemisus) are the best-known example. In these frogs, the skull, shoulder girdle, and forelimbs have been extensively reorganized compared to non-burrowing relatives. Their skulls are pointed and reinforced, their shoulders sit unusually far forward, and their forelimbs are broad and powerful. They essentially ram their heads into the ground and push soil backward with their front legs, more like a mole than a typical frog. Forward-burrowing frogs tend to have wider, sturdier upper arm bones with proportionally larger joint surfaces and muscle-attachment ridges, giving them the leverage needed to push through compacted earth.2Biological Journal of the Linnean Society. Comparative morphology of the humerus in forward-burrowing frogs
Why Frogs Go Underground
Frogs are permeable creatures. Their skin lets water pass through easily, which is great for absorbing moisture from damp surroundings but catastrophic in dry or freezing conditions. Burrowing solves this problem by giving them access to stable, humid soil layers where the temperature swings are gentler and desiccation is far less likely. In arid regions, digging underground is often the difference between life and death during the dry season.
Desert-dwelling species take this survival strategy to an extreme by entering a state called estivation, which is essentially the warm-weather equivalent of hibernation. The frog digs down, stops eating, and dramatically slows its body functions. The green-striped burrowing frog (Cyclorana alboguttata) of Australia can slash its whole-body metabolism by about 82% within five weeks of going underground.3Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. Metabolic depression during aestivation in Cyclorana alboguttata This is not a crude shutdown; the frog selectively dials down energy use in some organs while actually increasing it in others. Muscle and liver metabolism drop sharply, but kidney activity goes up, presumably to manage waste during the long underground fast. Most organs shrink to conserve energy, while leg muscles hold their size so the frog can dig its way out and move when rains finally arrive.
At the genetic level, estivation involves sweeping changes in which genes are switched on and off in skeletal muscle. Researchers who sequenced the muscle transcriptome of estivating Cyclorana found changes related to preventing muscle wasting, fighting oxidative damage, reshaping the internal cell skeleton, and managing programmed cell death.4PubMed. Frogs and estivation: transcriptional insights into metabolism and cell survival in a natural model of extended muscle disuse In other words, the frog’s body actively works to keep muscles from deteriorating during months of complete stillness, which is a problem that human medicine has struggled with in bedridden patients and astronauts in microgravity.
The Cocoon That Seals In Moisture
Some desert frogs have an additional trick. As they settle into their underground chamber, they shed layers of skin that dry into a parchment-like cocoon enveloping their entire body. This cocoon, formed from a single cell layer of shed outer skin, acts as a moisture barrier, dramatically reducing water loss through the frog’s otherwise highly permeable surface.5PubMed. Cocoon surrounding desert-dwelling frogs The frog may remain sealed inside this cocoon for months, breathing through just a tiny opening at its nostrils, waiting for the vibrations of rain hitting the ground above to trigger its emergence. Several unrelated frog lineages across Australia, Africa, and South America have independently evolved this cocoon strategy, which speaks to how effective it is as a solution to the same environmental problem.
Soil Preferences and Digging Behavior
Not all soil is equally inviting to a burrowing frog. When given a choice between wet sand and wet clay, green-striped burrowing frogs consistently chose sand. They buried themselves faster in sandy soil and dug deeper burrows.6Canadian Journal of Zoology. Effect of soil type on burrowing behavior and cocoon formation in the green-striped burrowing frog, Cyclorana alboguttata This makes intuitive sense: sand particles are loose and shift easily under the scraping motion of a hind foot, while clay compacts and resists displacement. For anyone who has tried to dig a hole in hard clay versus beach sand, the frog’s preference needs little explanation.
This matters ecologically because soil type can determine whether a burrowing species can actually persist in a given area. A patch of habitat might have the right rainfall pattern and food supply, but if the soil is too rocky or too dense with clay, a frog that relies on underground estivation simply cannot use it. Land-use changes that alter soil composition or compaction, like agricultural tillage or construction, can effectively eliminate underground refuges even when the surface looks fine.
Burrows as Megaphones
Burrowing is not just a survival tactic. Some frogs use their burrows as acoustic tools. Male frogs of the genus Eupsophus in South America call from inside their underground chambers, and the burrow’s shape amplifies those calls significantly. Playback experiments showed that calls broadcast from within a burrow gained an average of 3 to 6 decibels at a distance of one meter from the opening, compared to the same call played in the open.7PubMed. Extended amplification of acoustic signals by amphibian burrows A few decibels might not sound like much, but in acoustics a 6 dB gain roughly doubles the perceived loudness, meaning the burrow functions like a natural megaphone.
The amplification works both ways. Sounds from outside, including calls from rival males and bird vocalizations, were boosted by more than 6 dB inside the burrow. So the resident frog gets a louder broadcast to attract females and simultaneously gets a better listen to what is happening around it: where competitors are calling and whether predators are nearby. The burrow effectively serves as both a speaker and a parabolic microphone, which is a remarkably elegant dual function for what looks like a simple hole in the ground.
Feeding Underground
Most frogs surface to hunt, but a few species feed almost entirely below ground. The Mexican burrowing toad (Rhinophrynus dorsalis) is considered the most specialized underground ant and termite feeder among frogs. It spends nearly its entire life buried in loose soil, using a pointed, almost blob-like body to push through the substrate and a sticky, protrusible tongue to lap up ants and termites in their tunnels.8Journal of Zoology. Feeding specializations of the Mexican burrowing toad, Rhinophrynus dorsalis (Anura: Rhinophrynidae) Rhinophrynus surfaces only during heavy rains to breed in temporary pools, then vanishes underground again. Several other unrelated frog lineages also feed on subterranean invertebrates, but none seem as committed to it as this species.
Feeding underground means the frog does not have to risk predation at the surface to eat. It also means access to a food supply that is reliably present year-round in many tropical and subtropical habitats. The tradeoff is extreme body specialization: Rhinophrynus has tiny eyes, reduced limbs, and a body plan that looks almost nothing like a typical frog. It is so odd-looking that it was placed in its own family, the only living member of its lineage.
Cold-Climate Burrowing and Winter Survival
Burrowing is not only for desert heat. In temperate and subarctic regions, frogs dig into soil or leaf litter to survive winter. The wood frog (Lithobates sylvaticus) is famous for tolerating actual freezing of its body tissues, but even freeze-tolerant frogs do not just sit on the surface and hope for the best. They select sheltered spots under leaf litter or just below the soil surface, and their choice of microhabitat profoundly affects whether they survive the winter. Research has shown that the minimum temperature a wood frog experiences and the depth at which it settles into the substrate both explain significant variation in winter survival.9PubMed. Snow cover and late fall movement influence wood frog survival during an unusually cold winter
Snow cover plays a crucial role here, acting as an insulating blanket. A frog buried a few centimeters down under a thick snowpack may experience temperatures many degrees warmer than the air above. Modeling work on wood frogs has shown that differences in burrow depth and the concentration of cryoprotectants (sugars the frog produces to protect its cells from ice damage) interact with winter climate to determine the risk of lethal freezing and the risk of burning through energy reserves before spring breeding.10Ecosphere. Modeling the distribution of niche space and risk for a freeze‐tolerant ectotherm, Lithobates sylvaticus A frog that digs just a little deeper or picks a spot with better snow insulation can meaningfully shift its odds. This is part of why climate change and unpredictable snow years are concerning for these species: the margin between survival and death underground is surprisingly thin.
The Indian Purple Frog and Extreme Underground Living
If you want to see how far the burrowing lifestyle can reshape a frog, look at Nasikabatrachus sahyadrensis, the Indian purple frog. This species, found only in the Western Ghats mountain range of India, spends nearly its entire adult life underground. It occupies a deeply ancient position on the frog family tree, having diverged from its closest relatives tens of millions of years ago. Its life history is remarkable: the tadpoles live in mountain torrents, clinging to rocks with a large suction-cup mouth, then undergo one of the most dramatic metamorphoses known in frogs.11PubMed Central. From Clinging to Digging: The Postembryonic Skeletal Ontogeny of the Indian Purple Frog, Nasikabatrachus sahyadrensis (Anura: Nasikabatrachidae)
As they transform from tadpoles into juvenile frogs, their skeletons are rapidly overhauled. Young metamorphs initially dig backward, like most frogs, using a shortened lower leg bone and hardened structures on the hind foot. But as they grow, they appear to switch to headfirst burrowing, relying on a wedge-shaped skull, a shoulder girdle that sits unusually far forward, and spatula-shaped forelimbs. The adult purple frog looks almost nothing like what most people picture when they think “frog”: it has a bloated, purplish body, a tiny pointed head, and stubby limbs. It surfaces only briefly during the monsoon to breed, sometimes for as little as a few weeks per year. The rest of its life is spent underground feeding on termites and ants.
Convergent Evolution Among Burrowing Frogs
One of the more striking findings from studying burrowing frogs is how often unrelated lineages have converged on the same body plan. In Australia, researchers compared body shape between burrowing species from two distantly related frog families, the ground frogs (Myobatrachidae) and the tree frogs (Hylidae), which diverged from each other tens of millions of years ago. Despite that deep evolutionary separation, burrowing species from both families showed strong convergence in body shape, meaning they independently evolved similar proportions in response to the same underground lifestyle.12PubMed. Convergent evolution across the Australian continent: ecotype diversification drives morphological convergence in two distantly related clades of Australian frogs Short limbs, robust bodies, wide heads, and enlarged metatarsal tubercles keep appearing in burrowing frogs wherever they evolve, regardless of ancestry. The underground environment, it seems, imposes a narrow set of design solutions, and evolution keeps arriving at the same answers.
This pattern repeats globally. Headfirst burrowers in Africa and India share features like reinforced skulls and forward-shifted shoulders, even though they are not closely related. Backward burrowers on every continent converge on the spade-footed body plan. The consistency of these solutions suggests that the physics of moving through soil are demanding enough that there are only a few ways a frog-shaped animal can solve the problem efficiently.
Skin Microbes and Underground Health
Living underground exposes frogs to a world of soil microorganisms, and their skin microbiome may play a protective role. Amphibians globally face threats from the chytrid fungus Batrachochytrium dendrobatidis (Bd), which attacks the skin and has devastated frog populations on multiple continents. Researchers studying frogs that have persisted in the wild despite the presence of Bd found that their skin bacteria carry a wide variety of gene clusters linked to antifungal activity. These include genes for producing known antifungal compounds like fengycin and viscosin, as well as enzymes that break down chitin, a key component of fungal cell walls.13PubMed Central. Amphibian skin bacteria contain a wide repertoire of genes linked to their antifungal capacities
The connection to burrowing is indirect but worth noting. Frogs that spend time in soil are constantly in contact with environmental bacteria, and some of those bacteria colonize the skin and become part of the frog’s defensive microbiome. The soil environment itself, with its rich microbial diversity, could be a source of beneficial bacteria that help protect burrowing frogs against skin pathogens. Research in this area is still early, but the idea that burrowing frogs might gain some disease resistance simply from where they live is an intriguing possibility. Different bacterial families produce distinct antifungal compounds through different molecular mechanisms, so a frog with a diverse skin microbiome effectively carries a broader chemical arsenal.
Spadefoot Toads and an Evolutionary Puzzle
Spadefoot toads (family Scaphiopodidae in North America, Pelobatidae in Europe) are perhaps the most familiar burrowing frogs in the Northern Hemisphere. They spend most of their lives underground in arid or semi-arid habitats and emerge en masse after heavy rains to breed explosively in temporary pools. Their tadpoles are famous for developing at breakneck speed, racing to metamorphose before the pool dries up. It seems obvious that rapid larval development would be an adaptation to desert life, but the data paint a more nuanced picture.
A comparative study across spadefoot species found no relationship between how quickly the tadpoles developed and the aridity of the climate where those species live.14PLOS ONE. Evolution of Rapid Development in Spadefoot Toads Is Unrelated to Arid Environments The rapid development appears to have evolved before spadefoots moved into deserts, not in response to living there. This is a good reminder that just because a trait seems perfectly suited to an environment, it does not mean the environment drove its evolution. The burrowing habit and the fast tadpole development may have predisposed spadefoots to colonize arid regions, rather than the desert selecting for those traits after the frogs arrived.
This kind of evolutionary pre-adaptation, where an existing trait opens the door to a new lifestyle, shows up repeatedly in burrowing frogs. The powerful hind limbs that frogs already had for jumping turned out to be reasonably good for digging too, which likely made the evolutionary leap to burrowing easier than it would be for an animal starting from scratch. Once underground, natural selection then fine-tuned the details: harder spades, shorter legs, wider bodies, flatter skulls.