Axolotl (Ambystoma mexicanum): Facts, Habitat and Regeneration

What is an axolotl?

The axolotl is an amphibian, a member of the mole salamander family (Ambystomatidae), which also includes the tiger salamanders of North America. Most mole salamanders hatch as gilled larvae in water, then go through metamorphosis, lose their gills and spend their adult lives on land. The axolotl skips that last step.

Instead, it reaches adulthood and breeds while still in its larval body form, a trait biologists call neoteny or paedomorphosis. You can read more in why don’t axolotls turn into salamanders?. Despite its nickname “Mexican walking fish”, it is not a fish at all, as explained in is an axolotl a fish?.

The name comes from the Nahuatl language of the Aztecs. It is linked to Xolotl, a god associated with fire, lightning, death and transformation, and is often translated loosely as “water dog” or “water monster”.

What does an axolotl look like?

An axolotl has a broad, flat head, a wide mouth that seems to smile and small, lidless eyes. Its most striking feature is three pairs of feathery gill stalks that stick out behind the head like a frilly crown. These are covered in fine filaments that take oxygen from the water.

A fin runs along the back from just behind the head to the tip of the long, flattened tail, and continues underneath it. The legs are short and thin, with four toes on each front foot and five on each back foot. The skin is smooth and soft, with no scales.

Wild axolotls are dark: olive-brown to gray, with black spots and small gold or shiny flecks. They can lighten or darken slightly to match their surroundings. The pink and white axolotls seen in pet shops and laboratories are color forms bred in captivity. See what color are wild axolotls? for the full story.

How big do axolotls get?

Axolotls reach adult size at about 18 months to two years old. Most adults are 15–30 cm (6–12 in) long including the tail, and around 23 cm (9 in) is typical. Individuals longer than 30 cm (12 in) are rare. A healthy adult weighs roughly 60–110 g (2–4 oz).

Males and females look much alike. In the breeding season a male has a swollen cloaca (the opening under the base of the tail), while a female carrying eggs looks rounder and plumper.

Habitat and range

The axolotl has one of the smallest natural ranges of any well-known animal. It is native only to the high lakes of the Valley of Mexico, at an altitude of about 2,240 m (7,350 ft). It lived in Lake Xochimilco and Lake Chalco and probably in neighboring lakes such as Texcoco. Since Aztec times those lakes have been drained step by step, and most of the old lake bed now lies under Mexico City.

Today wild axolotls survive mainly in the network of canals and small lakes of Xochimilco, at the southern edge of the city. A small population has also been found in the lake of Chapultepec Park. Axolotls prefer cool, still water with plenty of underwater plants. The water at Xochimilco is usually below about 20 °C (68 °F) and can drop to around 6–7 °C (43–45 °F) in winter.

Diet and behavior

Axolotls are carnivores and were once the top predators of their lakes. In the wild they eat worms, insect larvae, small crustaceans, snails, small fish and tadpoles, and they will also eat smaller axolotls.

They hunt mostly by smell and by sensing movement in the water, and they can also detect weak electrical fields given off by prey. When something edible comes close, an axolotl opens its wide mouth very quickly. This creates suction that pulls water and prey inside. Its teeth are tiny, so it swallows food whole.

Axolotls are solitary and quiet animals. They spend much of their time resting on the bottom among plants and mud, walking slowly with their legs or swimming with sideways strokes of the tail. They can be active by day or night.

Besides breathing through their gills, axolotls have working lungs and sometimes swim to the surface to gulp air. Oxygen also passes through their thin skin. Their gills often look darker when the animal is calm and redder when it is active, because more blood flows through them.

Reproduction, life cycle and lifespan

In the wild, axolotls breed mainly in late winter and spring. Courtship follows the typical mole salamander pattern: the pair nudge each other and circle in a kind of dance, then the male deposits a small packet of sperm called a spermatophore on the bottom. The female picks it up with her cloaca, so fertilization happens inside her body even though there is no mating in the usual sense.

The female then lays her eggs one at a time, attaching each to a plant or stone. A clutch usually contains a few hundred eggs. The eggs hatch after about two weeks, and the tiny larvae are independent from the start, with no parental care. Young axolotls grow quickly and can breed at about one to two years old.

Unlike other salamanders, axolotls never leave this larval stage. They keep growing slowly through life, and their gills and tail fin stay with them as long as they live.

Lifespan in the wild is poorly known because so few wild axolotls remain to study. It is thought to be about 10–15 years. In captivity, axolotls often live 10–15 years, and some individuals have lived longer.

Regeneration: the axolotl’s famous superpower

Axolotls can regrow whole limbs, the tail, and parts of the spinal cord, heart, eyes and brain, usually without any scar. A lost leg is rebuilt with bones, muscles, nerves and skin in the right places over a period of weeks to months.

This ability has made the axolotl one of the most studied animals in biology, with large laboratory colonies in Europe and North America since the 1860s. In 2018 scientists published its genome, which is about ten times larger than the human genome. The details of how a lost limb grows back are covered in how do axolotls regenerate?.

Predators and threats

In the past, the main predators of axolotls were herons, egrets and other water birds, along with large fish. Today the main threats come from people:

• Habitat loss. The lakes of the Valley of Mexico have been drained, filled and built over as Mexico City has grown.
• Pollution. Xochimilco’s canals receive partly treated wastewater, and farm chemicals wash in from the surrounding fields, lowering oxygen levels and harming eggs and larvae.
• Introduced fish. Common carp and tilapia were stocked in the canals and lakes in the late 20th century to support fishing. They eat axolotl eggs and young, compete for food and churn up the bottom.

The axolotl appears to resist the chytrid fungus that has devastated many other amphibians, but its tiny remaining population makes it vulnerable to any new threat.

Conservation status

The IUCN Red List classifies the axolotl as Critically Endangered, with a decreasing population, and it is listed on Appendix II of CITES, which controls international trade. Surveys in Xochimilco recorded about 6,000 axolotls per square kilometer in 1998, about 1,000 in 2003, about 100 in 2008 and only around 35 in 2014. Estimates of the remaining wild adults range from roughly 50 to 1,000.

Conservation work focuses on cleaning the water and keeping out invasive fish. Researchers from the National Autonomous University of Mexico (UNAM) work with farmers who still use the traditional chinampas, the Aztec-era farm plots built between the canals. Some canals beside chinampas are fitted with simple filters and barriers that keep carp out and let axolotls live in cleaner water, while the farmers grow crops without heavy chemical use. More on this in are axolotls endangered?.

Millions of axolotls live in laboratories and aquariums around the world, but nearly all of them descend from a few dozen animals sent to Paris in the 1860s and are genetically different from wild axolotls. They are not a substitute for saving the wild population and its habitat.

Myths and facts

• Myth: the axolotl is a fish. It is an amphibian, related to frogs and newts. See also reptiles vs amphibians.
• Myth: wild axolotls are pink. Wild axolotls are dark olive-brown or gray. Pink and white forms come from captive breeding.
• Myth: there are plenty of axolotls, so the species is safe. The huge captive population hides the fact that the wild animals are close to extinction.
• Fact: an axolotl can change shape if forced. In laboratories, thyroid hormone can make an axolotl lose its gills and become a land-living salamander, but this almost never happens in nature.

Axolotls and people

For the Aztecs the axolotl was both a food and a sacred animal tied to the god Xolotl. In one legend Xolotl escaped death by changing into an axolotl and hiding in the water. Axolotls were eaten in the Valley of Mexico for centuries, and the animal remains a strong symbol of Mexico City today.

The axolotl appears in murals by Diego Rivera and on Mexico’s 50-peso banknote, introduced in 2021. It has also become a worldwide pop-culture favorite in games, toys and cartoons. Many conservationists hope this popularity can help protect the last wild axolotls in the canals of Xochimilco.