Axolotl

Name and taxonomy

The name comes from the Nahuatl word āxōlōtl. It has been translated as water dog, water monster, water servant or water twin. The word points to Xolotl, the Aztec god of fire, lightning and the dead, and the twin of Quetzalcoatl. In Spanish the animal is the ajolote, and GBIF also lists Mexican axolotl and Mexican salamander in English. The common name walking fish is wrong, because the axolotl is an amphibian, not a fish.

The species belongs to the family Ambystomatidae, the mole salamanders, in the order Urodela. Some writers prefer the name Mexican axolotl, because people also call the larvae of related species axolotls. In the wild it can be hard to tell from a tiger salamander larva or from a mudpuppy.

Evolution and relatives

The axolotl sits in the genus Ambystoma with the tiger salamander, and it belongs to the tiger salamander species complex. Its closest relative is the eastern tiger salamander of North America. A land-living tiger salamander also breeds in the same water as the axolotl. Many other Ambystoma species keep their larval form for life, or have populations that do. Sirens, mudpuppies and the cave olm are neotenic too, but no hormone can make them change.

Neoteny is thought to evolve where a high lake sits in country that is hostile to a land salamander. The axolotl lacks the hormone signal that tells the thyroid to make thyroxine, which drives metamorphosis. In laboratory animals the trait maps to a small region of one chromosome called met1. Those genes differ from the wild population, so complete neoteny in pets probably comes from artificial selection. The genome was published in 2018 at 32 billion base pairs, about ten times the size of a human's.

Appearance

The axolotl has a wide flat head, small eyes with no lids, and a fin that runs from behind the head to the vent. Three pairs of gill stalks stand out from the neck, each fringed with fine filaments. Four gill slits hide beneath them, lined with rakers that keep food out. The legs are small and weak, with long thin toes. The teeth are tiny and barely visible. Wikidata gives a length of 18 centimetres, which falls inside the range from other sources.

Adults range from 15 to 45 centimetres, with about 23 cm the usual size. Adults weigh about 0.06 to 0.11 kilograms. In the wild the skin is brown to tan, dusted with gold flecks over an olive tone. It can darken or lighten a little by changing its pigment cells, probably as camouflage. Captive animals come in leucistic pink, albino white, grey xanthic and near-black melanistic forms. Breeders often cross these, so a pink animal with pink eyes is common in the pet trade.

A male has a swollen cloaca lined with small papillae. A female has a smaller cloaca and a wide, rounded body when she carries eggs.

Habitat and range

The axolotl once lived across a linked system of lakes and wetlands in the highlands of central Mexico. It is known from Lakes Xochimilco and Chalco, and it probably lived in the larger Lakes Texcoco and Zumpango as well. The Aztecs began to drain these lakes, and the work sped up in the 20th century. Mexico City now covers most of the old lake bed.

Lake Chalco has been drained for drinking water and is gone. Lake Xochimilco survives only as a maze of canals and swamps at about 2,274 metres above sea level. The water there rarely rises above 20 °C and can fall to 6 or 7 °C in winter. The species prefers deep water and channels with thick water plants. A population also lives in the artificial lake in Chapultepec Park.

In 2019 the IUCN put the extent of occurrence at 467 square kilometres. GBIF holds records from 13 countries, but the records outside Mexico come from zoos, laboratories and pets.

Diet and hunting

The axolotl is a carnivore. In the wild it eats worms, snails, water insects, crayfish and small fish. It also eats other salamanders, including its own kind. Animal Diversity Web describes it as the top predator of its lake, which took anything it could catch.

It finds food by smell and snaps at anything that might be a meal. The mouth opens fast, and the drop in pressure sucks the prey in. As it sucks, the gill rakers lock together to close the gill slits. In captivity it takes trout pellets, bloodworms, earthworms and waxworms. Feeder fish can carry parasites, so keepers use them with care. Like other cold-blooded animals, it eats less in cool water because its metabolism slows.

Behaviour and social life

The axolotl is solitary. It may be active at any hour, though the site fields list it as nocturnal. It spends most of its time on the bottom. It breathes through its gills, and it can also rise to gulp air into its lungs. The gulp can push air straight to the lungs or send it back and forth in a four-stroke pattern.

It keeps growing all its life. Some researchers think this constant growth is part of why it regenerates so well. Where carp and tilapia have arrived, wild axolotls move less to avoid being eaten. That stillness costs them hunting and mating chances. Captive animals seem to swallow gravel, and some may use it to grind food, but the evidence is thin.

Communication and senses

Axolotls signal to each other almost only in the breeding season. Then they use sight and scent. For the rest of the year, Animal Diversity Web reports little or no contact between them. They are not known to make any call, which is typical of salamanders.

Their senses are built for dark, weedy water. They can detect the weak electric fields that other animals give off. They also use sight and chemical cues to find prey. Smell matters most in the hunt, and a hungry axolotl snaps at any scent of food. A 2025 study found a two-way signal path between the brain and the eye that is not known in other animals.

Reproduction and life cycle

Wild axolotls breed from March to June. Courtship follows the pattern of other mole salamanders. Each animal nudges the other's cloaca, and the pair then circle each other in a slow dance. The male moves off with his tail waving, and the female follows. He shakes his tail hard for about half a minute and drops a spermatophore, a cone of jelly with sperm on top. The female walks over it and picks it up with her cloaca.

She lays 300 to 1,000 eggs, one at a time, on rocks and water plants. Each egg sits in its own jelly coat, because it needs more oxygen than a frog egg in a clump. The eggs hatch after 10 to 14 days. The larvae are independent at once and get no care. Young from the last season are ready to breed by the next one. The generation length is about 5.5 years.

There is no metamorphosis in the wild. The larva simply grows, keeps its gills and fin, and matures at about 1.5 years, or 18 to 27 months in captivity. A hormone injection can force the change into a land salamander that looks like a plateau tiger salamander. Such an animal grows eyelids, loses its gills and fin, and regenerates far less well. Captive axolotls usually live 5 to 6 years, and some reach 15. Wikipedia gives a wild life expectancy of 10 to 15 years.

Predators and threats

Before people brought in fish, the axolotl had few enemies in its lake apart from larger axolotls. Now Nile tilapia and common carp eat its young and compete for its food. Herons take adults, and great egrets ate several captive-bred animals released in a 2025 study. Large fish are new to the lakes, and Animal Diversity Web blames them for much of the decline.

The larger threat is the water itself. Xochimilco is fed with partly treated wastewater, and its water is low in oxygen. Farm pesticides wash in and kill embryos and larvae, and the survivors show deformities and odd behaviour. The wild population has passed through several bottlenecks, so inbreeding is high and genetic diversity is low. The chytrid fungus has been found on axolotls, but the species resists it and the disease is not thought to threaten it.

Population and conservation

The IUCN lists the axolotl as Critically Endangered, and Mexico lists it as in danger of extinction. Surveys of Lake Xochimilco found 6,000 animals per square kilometre in 1998, 1,000 in 2003 and 100 in 2008. A four-month search in 2013 found none, though two turned up in nearby canals a month later. The wild population is now put at 50 to 1,000 adults. It sits on Appendix II of CITES, which controls trade.

Conservation now leans on captive breeding. Animals raised in semi-natural ponds can catch prey and escape predators with moderate success. The National Autonomous University of Mexico held 100 captive-bred axolotls in 2021, mostly for research. It plans a breeding population in a semi-artificial wetland on the campus. A 2025 release study found that recaptured animals had gained weight in the wild. Released animals may still meet the fate of the wild ones if pollution and invasive fish remain.

Laboratory axolotls carry some tiger salamander DNA, so they may not be a clean stock for reintroduction. Most captive animals descend from a single group of under 36 individuals. Few field studies exist, so the ecology of the wild animal is poorly known.

Relationship with humans

The Aztecs ate axolotls and used them as medicine. Alexander von Humboldt wrote that the conquered Mexicans fed on water plant roots, insects and this doubtful reptile. It is still eaten now and then, roasted or boiled, with the tail dipped in vinegar or cayenne. In 1863 a shipment of 34 adults reached the Jardin des Plantes in Paris. Auguste Duméril was startled when some turned into land salamanders, and the study of neoteny began there.

Vilém Laufberger in Prague first forced the change with thyroid hormone, and Julian Huxley repeated it with ground thyroid. Today the axolotl is a model organism for limb regeneration, heart defects, neural tube closure and stem cells. Its large embryo lets researchers watch a vertebrate develop from the first cell. It is also a popular pet, kept at 16 to 18 °C in a tank of about 150 litres with no gravel. iNaturalist holds 2,889 observations, most of them of captive animals.

In culture and myth

In Aztec myth the gods had to die to set the sun moving, and Xolotl refused. He hid as a maize plant, then as an agave, and at last as an axolotl, but he was caught in the water. The animal took his name and became a symbol of change and of doubleness. Xolotl also ruled over dogs, games, twins and ugly beings, which may explain the name water dog.

Axolotls appear in Diego Rivera's 1951 mural Water, the Origin of Life in Chapultepec Park, and on many walls in Mexico City. The city made the axolotl its official emoji in 2017. In 2021 Mexico put it on the new 50-peso note, which won Bank Note of the Year. By 2025 the Bank of Mexico reported that up to 50 million of the notes were being hoarded.

In Japan a 1980s Nissin Foods campaign named the animal the wooper looper, and the name stuck. The Pokémon Wooper, from 1999, is based on it, and Mudkip in 2002 borrows from it. Minecraft added axolotls in 2020 to draw attention to endangered species. Toothless, the dragon in How to Train Your Dragon, was modelled on the axolotl. Julio Cortázar wrote a short story called Axolotl set at the Paris aquarium, and a star in Cetus was named Axólotl in 2019.