From the largest elephant to the tiniest mouse, the earth is roamed by animals big and small that we can spy from behind telescopes, in hides or on safaris. But what about those that inhabit the subterranean world we rarely see?
Here, we take a look at just some of the curious mammals, reptiles and amphibians across the continents that dig, burrow and tunnel their way through life, invariably at the expense of arthropods like ants and termites and illustratively featuring the word ‘mole’ somewhere in their name.
Underground animals
Naked mole-rats
Small, blind and almost completely fur-free, the fascinating naked mole-rat is one of only a few eusocial mammal species, meaning they live together in large colonies with just one breeding female, the queen.
They inhabit wide webs of tunnels and distinct chambers (think separate larders, sleeping burrows and toilets) running for up to 2.5 miles (4 km), occasionally surfacing for a touch of sunshine.
Omnivorous with long, strong incisors that move independently, they eat roots and bulbs, even their own feces to maximise nutrient intake. Mole-rats live long (a record of 32 years), healthy lives and thrive in dark, low-oxygenated ecosystems throughout the Horn of Africa.
Not only are they one of the weirdest rats and strangest rodents in the world they are also one of the weirdest animals on Earth
Blind snakes
One of the weirdest snakes in the world and part of the typhlopoidea family with more than 200 sub-species, blind snakes are found in tropical regions around the globe, notably in Africa, Asia, America and southeastern Europe.
Although appearance varies by species, they're generally small, thin with short tails, pinky grey and covered in smooth scales, which is why they’re often mistaken for worms despite having tiny eyes underneath their head scales, which greatly reduce their vision.
Sometimes seen on the ground at night or after heavy rainfall, these non-venomous snakes live their lives, which can span from four to 20 years, almost entirely underground, dining on arthropods with a particular penchant for termites and ants.
European moles
The work of a mole is seen far more frequently than the mammal itself, whose short black coats and pointy pink noses reside beneath mole hills that pop up in woodlands, fields and manicured lawns across Europe.
These subterranean dwellers are rarely spied as they are busy using their giant be-clawed front paws to tunnel through as much as 20 metres of earth per day in search of their favourite treat, earthworms, and to build their burrows.
Small and sturdy with a lifespan of up to four years, they are also champions of biodiversity, aerating the soil they churn, distributing seeds, aiding habitat regrowth and soil drainage.
Burrowing asps
Burrowing asps, of which there are 19 species, are unique in the snake world for their ability to inject venom through a virtually closed mouth. As their nickname ‘side stabbers’ suggests, they can push their long-fanged lower jaws out and swing their heads to deliver a stab of highly toxic, although not fatal to humans, venom.
Typically found across the tropical regions of Africa and the Middle East, this manoeuvre is handy for killing prey in confined spaces beneath the ground. Thin, shiny black with a pointy head, these elusive snakes average 50 cm (20 inches) and feed on fellow burrowers, mainly small rodents, amphibians and reptiles.
Mole crickets
Step forward one of nature's most bizarre creatures, the mole cricket. As its name hints, it has the body of a cricket but the scaled-down head, front legs and tiny eyes that resemble its namesake.
Found in grasslands and fields worldwide, and sometimes considered a pest, mole crickets use their spade-like front legs to tunnel both forwards and backwards at speed, where they spend the majority of their lives. Diets vary, as some are herbivores while others are omnivores.
Male mole crickets attract females to their burrows for breeding with an especially loud chirp. Believed extinct in the UK, this chirp led to their rediscovery in the New Forest in the early 2000s.
Rose’s rain frogs
The bulbous Rose’s rain frog, with its white underbelly, brown back, black speckles and look of a scowl, is one of 20 species of the breviceps family of amphibians that live their lives largely nesting below the surface.
Rose’s rain frogs are endemic to coastal areas of the southwestern Cape of South Africa and are generally found in shrubland with soft, sandy soil. Emerging after heavy downpours, they hunt bugs and grubs like ants, termites and woodlice. As they can’t swim, eggs are laid in nests where tadpoles develop in the shell before hatching as fully formed baby frogs.
Mole salamanders
The glossy, spotted-back form of a mole salamander can be found in the southeast and central United States, where terrestrial adults evolve to live in underground burrows they’ve either built or commandeered, coming to the surface to hunt and breed in water. The wider species includes paedomorphic mole salamanders, which remain aquatic and live in bodies of water such as ponds.
With a lifespan of 10 to 20 years, these solitary amphibians, which have short, stocky bodies topped with far larger heads, feast on arthropods, eggs and even other amphibious species.
Sand boas
The sandy-toned sand boa, of which there are 18 species found in dry regions worldwide, spends much of its time, anywhere from 10 to 27 years, with its body below the arid surface, although its head can remain close to the ground ready to strike passing prey.
Despite the name, these slow moving, non-venomous snakes lodge in sandy soil rather than pure sand; they're voracious diggers, arguably one of the best snake excavators in the business.
Reaching between roughly 60 cm and 90 cm (2 ft and 3 ft) in length, sand boas are typically thick snakes with stubby tails covered in strong, keeled scales spattered with intermittent dark spots.
Pocket gophers
The pouchy-cheeked pocket gopher, of which there are no fewer than 41 species endemic to North and Central America, is a small brown omnivorous mammal found largely underground but will venture, rarely and briefly, above the surface for food, especially in summer, and on the hunt for materials to line their burrows.
The typical pocket gopher lives between one and three years in burrows tunnelled in soft, sandy soil. They're easily identifiable by their protruding long incisors, which can close behind their mouths to keep dirt out while digging. They have small ears and eyes, effective whisker-sensors and, crucially, strong claws ideal for tunnelling.
Nine-banded armadillos
While technically not a full-time subterranean resident, the nine-banded armadillo is surely one of the quirkiest fossorials (animals that burrow underground). Covered in hard shells, scales and skin, they spend most of their lives, typically around seven years, in deep burrows across the Americas.
Nocturnal, they have a largely insect-based diet, topped up with small amphibians and reptiles in winter, and can sniff invertebrates through soil up to 20 cm away, their sensitive noses and good hearing making up for their typically poor eyesight, while their sticky tongues are handy for scooping out termites.
For added confusion, not all nine-banded armadillos actually have nine bands as this depends on their location.