The Natural Habitat and Unique Appearance of Axolotls: What Makes Them So Fascinating?

The axolotl (Ambystoma mexicanum) has deep roots in ancient mythology. According to Aztec legend, the god Xolotl transformed himself into this small, feathery creature to evade capture, giving rise to the species in the lakes near present-day Mexico City.

As one of the earliest modern zoo inhabitants, 34 axolotls were transported from Mexico to the "Jardin zoologique d'acclimatation" in Paris in 1864, alongside deer and wild dogs. But where do axolotls live in the modern world, and what explains their otherworldly appearance?

Where Do Axolotls Live?

Axolotls, a sizable and endangered salamander species, inhabit freshwater environments, particularly Lake Xochimilco in southern Mexico City. Despite being nicknamed "Mexican walking fish," they are amphibians, not fish.

What Do Axolotls Look Like?

In their natural habitat, axolotls typically display dark brown or black coloring with speckles. However, leucistic or albino variations are frequently observed, especially in domesticated settings.

Wild axolotls are undeniably adorable, with their rounded heads and perpetual smiles, making them popular in the pet trade. This charm is partly due to neoteny, a phenomenon where they retain juvenile characteristics into adulthood.

For example, adult axolotls possess functional lungs and can breathe through their skin, similar to other amphibians. However, they retain large, feathery external gills, a feature most amphibians lose after their juvenile stage.

Axolotls have tiny, fragile webbed feet and a lengthy, tadpole-like tail adorned with a translucent fin. Since they don’t rely on their feet for land movement, their tails help them navigate through water efficiently.

Stable Habitat, Stable Features

Researchers believe axolotls retain their juvenile traits because their natural habitat is exceptionally stable. Unlike other salamanders, such as tiger salamanders, which inhabit wetlands that periodically dry up, axolotls didn’t need to shed their gills or adapt to terrestrial environments.

Wild axolotls developed in an environment with constant water availability and minimal aquatic predators. This stability allowed them to avoid the energy-intensive process of adapting their bodies to changing conditions.

The Axolotl's Life Cycle

In captivity, axolotls can live up to 15 years, but their lifespan in the wild is usually limited to five or six years. They become sexually mature at one year old. Although generally solitary, wild axolotls begin seeking mates during February's breeding season, with males using pheromones to locate females.

During mating, the male performs a courtship display by shaking his tail toward the female. Once she accepts, she nudges him with her nose, prompting him to release a sperm packet onto the lake floor. The female then collects it to fertilize her eggs.

After laying hundreds of eggs among weeds or rocks, the female wild axolotl abandons them, providing no parental care to the hatchlings.

Newly hatched axolotls, driven by hunger, have been known to nibble on their siblings' legs and tails. This behavior is harmless, as their remarkable regenerative abilities allow the lost limbs to grow back.

Pink Predators

In their natural habitat, axolotls once reigned as apex predators in the lakes, wetlands, and canals of central Mexico. Unlike most salamander species, which transition to land and breathe with lungs as adults, axolotls spend their entire lives underwater, relying on their feathery gills for respiration.

Despite their gentle appearance, axolotls are fierce carnivores, preying on worms, mollusks, insects, larvae, and even small fish in the wild.

Regenerative Abilities

The Aztec mythos surrounding axolotls highlights their near-immortality, as they can regenerate almost any lost body part with ease. While lizards can regrow tails, flatworms can regenerate halves, and starfish can regrow limbs, axolotls surpass them all by regrowing virtually any body part within weeks.

"Among vertebrates, salamanders are unique in their ability to regenerate without scarring," explained David Gardiner, a professor at the School of Biological Sciences, University of California, Irvine, during a 2019 interview. "While other salamanders can regenerate, axolotls excel at it."

Once Europeans discovered axolotls' regenerative capabilities, they transitioned from zoo curiosities to becoming one of the most significant and enduring laboratory animals in scientific history.

Georges Cuvier, often hailed as the Father of Paleontology, studied axolotls to determine if Carl Linnaeus was justified in separating the Amphibia and Reptilia classes. Cuvier theorized that axolotls, with their lifelong gill-based respiration, were a type of lizard stuck in a larval stage — what paleontologist Stephen Jay Gould called a "sexually mature tadpole." (While Cuvier was occasionally correct, this was not one of those times.)

Due to their adaptability in laboratory and aquarium environments, 19th-century zoologist Auguste Duméril distributed axolotls to labs across Europe. This led to disturbing experiments where scientists mutilated axolotls to explore the boundaries of their regenerative capabilities.

Scientific Studies Surrounding Axolotls

Researchers are fascinated by axolotls, aiming to harness their extraordinary limb regeneration abilities for human medical applications. Axolotls can regrow limbs, heart tissue, eyes, spinal cords, and even parts of their brains, continuously producing new neurons throughout their lives — a trait shared, though less efficiently, by human brains.

"Axolotls are now pivotal in regeneration research," Gardiner explained. "For centuries, we've known that embryonic structures can repair themselves when parts are removed. However, in most animals, like mammals, this ability diminishes after embryonic development. Axolotls and other salamanders can revert to an embryonic-like state, reactivating dormant developmental programs. Humans possess these programs but lose access to them post-embryo. Essentially, we've evolved both the capacity to regenerate and mechanisms to suppress it."

Axolotls can be forced to metamorphose into gill-less adult salamanders through iodine or thyroxine injections or iodine-rich diets. However, post-metamorphosis, their regenerative abilities significantly decline.

The Dangers Facing Wild Axolotl Populations

Despite their extraordinary regenerative abilities, which allow them to reaccess embryonic states to heal and regrow body parts, wild axolotls struggle to survive in their natural habitats. Their ecosystems are increasingly threatened by invasive predators, pollution, and habitat destruction, challenges even their remarkable resilience cannot overcome.

The lakes surrounding Mexico City, once a thriving habitat for axolotls, are now polluted due to outdated wastewater systems. Additionally, invasive species like tilapia and perch, which axolotls naturally prey on, have further disrupted their environment, pushing the species toward endangerment.

Conservation Efforts

To protect the endangered axolotl, the Mexican government and various conservation organizations are working tirelessly to restore the lakes and natural habitats crucial to the species' survival.

One approach involves creating stationary floating habitats known as chinampas — rafts constructed from aquatic plants, mud, and wood, which were historically used as floating gardens in ancient Mesoamerican cultures.

Centuries ago, when the Aztec capital of Tenochtitlan occupied the area now known as Mexico City, the Aztecs cultivated vast networks of chinampas. These agricultural systems formed shallow, protected canals where axolotls flourished.

Following the arrival of European conquistadors in 1519, the Aztec civilization was dismantled, the chinampas were destroyed, and the canals and lakes were drained.

Today, the wild axolotl population is confined to Lake Xochimilco. Efforts are underway to eliminate invasive species that threaten axolotls and reintroduce chinampa-based agriculture. The aquatic vegetation of chinampas not only provides a habitat for axolotls but also helps purify the lake water by filtering out toxins.

Ecotourism centered around these chinampas has played a significant role in funding conservation initiatives for axolotls.

Captive Axolotl Populations

While wild axolotls face significant challenges, captive populations are thriving. They are now the most globally widespread amphibian species.

Driven by scientific interest in their regenerative abilities, millions of axolotls reside in laboratories worldwide — far outnumbering their wild counterparts. Beyond research, axolotls are also popular pets, particularly in Japan, where they are even served as a deep-fried delicacy in certain restaurants.

Important Notes for Pet Owners

Before acquiring an axolotl, ensure it is legal to keep one as a pet in your area, as regulations vary. Since axolotls are fully aquatic, their tanks must be completely filled with water, with a 15- to 20-gallon (57- to 151-liter) tank being ideal.

Similar to small fish, axolotls should never be picked up or handled. Additionally, they should not be housed with other pets, whether fish or another axolotl, as they are solitary creatures and do not coexist well with others.

By adhering to these simple guidelines, you’ll find axolotls to be resilient and low-maintenance pets. However, it’s crucial to treat this critically endangered species with the utmost care and respect.