Mexican Mole Lizard

ReptileMexico

Sep 15

Bipes biporus

The Mexican mole lizard digs intricate tunnels that run below the surface of the soil. To regulate its body temperature, the mole lizard moves to tunnels at different depths — it spends cooler mornings near the surface and as the day heats up, it moves deeper and deeper below ground.

The dry soil bulges as something long and sinuous moves beneath the surface. The shape moves below a desert scrub and the soil churns, revealing the coils of a pink, cylindrical body. As it surfaces, it unveils more and more of its serpentine length, unwinding to some 20 cm (8 in) long and lined with vertical rings, like some oversized earthworm. But at one end, the creature's body terminates in a scaley, flattened nub set with beady black eyes and a wide gummy-looking mouth. Just beneath this simple head, are a pair of tiny limbs, each brandishing five long-clawed digits and forming wide, shovelling shapes — very much like the paws of a mole.

This creature straddles the line between myth and reality. It looks like the larval form of a wyrm, or an unnatural hybrid of several real-world species. Its body — long and cylindrical, shining, ringed, and pink — is that of an earthworm. Its bony head, decorated in a mosaic of different-sized scales, looks like a primitive lizard. While its forelimbs — its only limbs — are stubby, clawed shovels, borrowed from a burrowing mole.

Mexico's Mysterious Monster

This creature's name, the Mexican mole lizard, sheds little light on its mysterious origins — it's certainly not a mammalian mole and it's not quite a lizard either — but it does reveal its place of dwelling.

The Baja California peninsula juts from the northwestern tip of Mexico like a rugged arm reaching into the Pacific. On one side are the battering waves of the ocean, on the other, the rich deep waters of the Gulf of California. In between are deserts and windswept dunes, scrub forests and coastal plains, supported by a spine of jagged mountains. ¹

This mole lizard ranges from the flat Magdalena Plain along the southern coast to the sands of the Vizcaíno Desert further north. The soil here is loose and dry; perfect for burrowing. And the mole lizard is fossorial, or, in other words, adapted to burrowing. Its limbs look so mole-like because they've evolved to serve the same function; pushing soil out of its way. And its body, while looking very worm-like, moves more like some types of snakes. The technical term is 'concertina locomotion', but what it amounts to is this: the mole lizard anchors a part of its body against a tunnel wall, then pushes the front portion of its body off of that anchor point to inch forward. Then it re-anchors and repeats. All the while, its front limbs shift soil and stabilise its body — and with no hind limbs to speak of, its back end slithers smoothly through its tunnels.

The mole lizard's life is one of darkness and confined spaces within winding tunnels just beneath the surface of the soil. Its intricate tunnel system stretches out wide horizontally but doesn't seem to go very deep — according to one study, at least, which discovered most mole lizards at a depth of 4 cm (1.6 in) and a max depth of 15 cm (5.9 in). But, more research needs to be done to define the extent of this creature's subterranean limits.

The mole lizard's tunnels do go deep enough to create a gradient of differing temperatures. Ectothermic — with its body temperature largely determined by its surrounding environment — the mole lizard regulates its internal temperature by moving between different depths. During the cooler hours of the morning, the mole lizard spends time in the upper spaces of its subterranean home, perhaps just 2.5 cm (1 in) below the surface. But, as the sun fully rises, baking the upper layers of the soil, the mole lizard escapes the sweltering heat by moving into deeper chambers where the soil remains cool. Through these daily migrations, the mole lizard stays active year-round, no matter the temperature of the surface world.

Bowel-ripper or Bug-eater?

Among the locals of Baja California, there circulates a tale of an insidious creature. A creature that preys on people when they're at their most vulnerable. It lies in wait, hidden, until its victim must relieve himself. When he squats to do his business, the creature springs up into his, um, orifice. It tunnels through his insides, just like it does through the soil, ripping and tearing through his guts until a truly unpleasant death takes him.

As far as is known, there exist no butt-burrowing creatures in Baja California, and the Mexican mole lizard certainly has no wish to end up inside a person's digestive tract. It is, in fact, completely harmless to humans. The mole lizard's actual targets are much smaller; ants, termites, cockroaches, or any other number of small invertebrates and their eggs or larvae. Once the mole lizard sets upon a large meal — say, a party of ants — it'll eat until its stomach is full, munching on them with its conical teeth.

To catch its prey, it must sometimes venture outside of its tunnel system, to the surface. It does so at dusk when the sun is in retreat. Spending so much time in the dark below, the mole lizard's skin lacks the melanin that gives surface-dwelling animals colour and protection from the sun's rays. The mole lizard even appears to lose pigment throughout its life; starting out a vivid pink and turning pale white as it matures. You could take a flashlight to the mole lizard's skin and watch it turn translucent.

The mole lizard leaves its tunnel system through exit holes concealed beneath rocks or logs. With its pin-prick eyes and lightless subterranean home, its vision is as poor as you'd expect. Its hearing, however, is surprisingly good. Many animals, highly specialised for a subterranean existence, "hear" by feeling vibrations via direct contact with the soil, rather than by picking up soundwaves travelling through the air. Conversely, the Mexcian mole lizard has retained structures within its ears, connected to the deep folds of skin on its neck, which allow it to pick up airborne sounds — likely an adaptation for hunting above ground. Once its meal is caught, the mole lizard slinks back to its burrow, down into its tunnels to consume its prey.

A Hypogean Hunt

A spotted leaf-nosed snake (*Phyllorhynchus decurtatus*) — hunter of the Mexican mole lizard.

The mole lizard's forays to the surface expose it to the dangers of lizard-eating birds, badgers and skunks. But its deadliest predators hunt it in its own home. A mole lizard's tunnels are shaped to fit its form; perfect for long, cylindrical, serpentine bodies. Burrowing snakes, like the spotted leaf-nosed snake, slither through the sand in search of prey. By burrowing into a mole lizard's tunnel system, the snake essentially discovers a highway to its next meal. The mole lizard is pursued by an agile killer through a narrow maze of its own making.

While it has no offences, the mole lizard has one defence — albeit one that comes at a permanent price. With a snake closing in behind it, the mole lizard can detach its tail, leaving the appendage behind to wriggle and distract its pursuer, or possibly block the tunnel and prevent the serpent from following further. However, this appears to be a one-time trick, as the mole lizard's tail doesn't regrow. Still, it's better to lose your tail than your life.

The Legged Legless Lizard

We've seen how the mole lizard burrows and moves, where it lives (underground) and where it doesn't (up people's butts), what it eats and what eats it. Knowing all of that, can we finally determine what it really is?

Clockwise from top; a Florida worm lizard (*Rhineura floridana*), red worm lizard (*Amphisbaena alba*), and checkerboard worm lizard (*Trogonophis wiegmanni*).

Well, it’s certainly a reptile, with its scaley skin and ectothermic ("cold-blooded") physiology. It belongs to the order Squamata, with the snakes and lizards, but it's not really either of those. It is part of a group known as the amphisbaenians — around 180 species commonly referred to as worm lizards. This common name is very apt for the majority of amphisbaenians, even more so than for the mole lizard, as most of the 180 species are completely limbless, with almost indistinct heads. This group likely evolved its legless-ness separately from snakes and is actually thought to be more closely related to lizards (and considered true lizards by some taxonomists).

Some examples of amphisbaenians include the Iberian worm lizard, Florida worm lizard, and smallhead worm lizard — which could easily be confused for earthworms (if they keep their mouths shut) — and the chunkier checkerboard worm lizard, crooked worm lizard, and red worm lizard.

A four-toed mole lizard (*Bipes canaliculatus*) on the top and a three-toed mole lizard (*Bipes tridactylus*) on the bottom.

The Mexican mole lizard, along with its two cousin species, make up a unique group within the amphisbaenians — unique in that they're the only ones with any limbs. The mole lizards, in the family Bipedidae and its sole genus Bipes, are named for their 'bipedal' (two-limbed) body plans. Interestingly, each of the three species has a different number of digits on their remaining front limbs; the Mexican ², sometimes called the five-toed worm lizard, has five digits on each, the four-toed mole lizard has four, and the three-toed has three. While they seem to lack any hindlimb at all, an X-ray will reveal tiny vestigial bones — remnants of legs their ancestors once walked upon.

Animals of the Baja California Peninsula

From top to bottom; a white-tailed antelope squirrel (*Ammospermophilus leucurus*), zebra-tailed lizard (*Callisaurus draconoides*), and Gila woodpeckers *(Melanerpes uropygialis*).

¹ Despite being mostly quite dry and scrubby, the Baja California peninsula hosts a bounty of interesting animals.

Several of the species that occur here also range more widely throughout North America. White-tailed antelope ground squirrels lay belly down on shady rocks to cool down. Zebra-tailed lizards dash across burning sands with their toes curled upwards, alternating between their front and hind limbs. Odd burrowing owls dig dwellings in the sands and bound about on stilt-like legs. Kit foxes, with their large ears and small statures — the smallest canids in N. America — slink out of their dens at night to hunt kangaroo rats and jackrabbits. Coveys of rotund California quail roam the scrublands, scratching at the ground for tidbits to eat. Gila woodpeckers and tiny elf owls peek out of their saguaro cacti nesting hollows. In the mountains, bighorn sheep bash heads in in concussive clashes. While pronghorns sprint across the lowlands, unmatched in speed, chased by the ghosts of American cheetahs.

From top to bottom; a red diamond rattlesnack (*Crotalus ruber*), Baja California legless lizard (*Anniella geronimensis*), and vaquita (*Phocoena sinus*).

In addition to all the sprinters, fliers, and borrowers, the peninsula is home to a serpentine menagerie that would beguile any herpetologist. There are rosy boas, both coastal and desert, non-venomous striped racers and very-venomous red diamond rattlesnakes. There are coachwhips, sidewinders, king snakes, and thread snakes, among many others.

There are also more exclusive species, rarely, if ever, found outside of the peninsula and its surrounding islands. Just off the coast lies the island of Espiritu Santo, where the black jackrabbit (a close relative to the black-tailed jackrabbit) lives predator-free, sheltered from the jaws of foxes and coyotes by a stretch of sea. Several lizard species bask in the Baja California sun — from blue rock lizards to spiny-tailed iguanas to horned lizards that resemble spiky whoopee cushions — weathering the heat and aridity with their tough, scaly skin. The peninsula even has its own endemic legless lizard (quite unrelated to the worm and mole lizards). At the peninsula's very southern tip lives an endangered vesper bat called the peninsular myotis while Santa Catalina Island, in the Gulf of California, is home to an endemic and critically endangered rattlesnake.

Speaking of the Gulf of California, it would be remiss to not at least mention the wildlife found in Baja California's surrounding seas. The gulf has been called the "world's aquarium" and is one of the most diverse marine environments on Earth, with a recorded 6,000 animal species (and an estimated 6,000 more to still be discovered). There are mammalian goliaths like blue and fin whales, there is the whale shark — the largest shark to ever live — and the giant Humbolt squid. Five of the seven living sea turtle species frequent these waters. 900 species of fish have been recorded here and over 5,000 species of micro-invertebrates. California sea lions and southern elephant seals rest upon the beaches, while birds — gulls, pelicans, sandpipers, cormorants, etc. — line the shores. One final animal worthy of mention is a little porpoise; the vaquita. The smallest of all living cetaceans, this critically endangered species (with only around 10 - 20 individuals left) is found only at the northern end of the Gulf of California.

² Technically, all three mole lizard species could be called the "Mexican mole lizard", not just the five-toed (Bipes biporus), since they're all endemic to Mexico.

**Where Does It Live?**

⛰️ Deserts and shrubslands, where it burrows in loose soil.
📍 The Baja California peninsula in Mexico.

‘Least Concern’ as of 01 March, 2007.

IUCN

Size // Small
Length // 18 – 24 cm (7.1 – 9.4 in)
Weight // 85 grams (3 oz)
Activity: Diurnal and Crepuscular☀️/🌅
Lifestyle: Solitary 👤
Lifespan: Over 3 years
Diet: Carnivore
Favorite Food: Small invertebrates 🐜
Class: Reptilia
Order: Squamata
Family: Bipedidae
Genus: Bipes
Species: B. biporus

The Mexican mole lizard is endemic to the deserts and shrublands of the Baja California peninsula in northwestern Mexico.

This species can grow to be as long as 24 centimetres (9.4 inches). As it matures, its body turns from a vivid pink to a pale white.

The mole lizard moves using 'concertina locomotion' — anchoring one part of its body against the tunnel wall, pushing the front portion of its body off of the anchor point to move forward, then re-anchoring at a further point and repeating.

Its two limbs have five fingers each; tipped with sharp claws and flattened like the forepaws of a mole. Indeed, it uses them much as a mole does, to push dirt out of the way as it digs.

The Mexican mole lizard's most dangerous predators are snakes, especially burrowing snakes, which pursue the mole lizard through its tunnel system.

To escape predators, the mole lizard can drop its tail — leaving it behind to wriggle and distract its attacker or block the path of a tunnel. Its tail, however, doesn't regrow, so it can only pull the move once.

Able to move to warmer or cooler parts of its tunnel system, the Mexican mole lizard can stay active year-round, no matter the temperature of the above world.

This lizard has no hindlimb anywhere along its lengthy body — not visible ones, anyway. But, under an X-ray, you can see the tiny vestigial bones that made up the hindlimb it's ancestors once had.

The mole lizard is a reptile, but not exactly a lizard. It belongs to a group called amphisbaenians, which contains over 180 species commonly referred to as 'worm lizards'.

Including the Mexican mole lizard, there are three mole lizard species. The other two are the four-toed mole lizard (Bipes canaliculatus) and three-toed mole lizard (Bipes tridactylus). They're all endemic to Mexico and are the only amphisbaenians with limbs.

Each mole lizard species has a different number of digits. The Mexican mole lizard is also called the five-toed mole lizard, because of its five-toed forelimbs.

Slight content warning!
There is a belief among some locals in Baja California that, when an unwitting person squats to relieve themselves, the mole lizard will burrow up the person's orifice and kill them by tearing their intestines.

The mole lizard is actually harmless to humans.