What is an axolotl?

By Alice Lipscombe-Southwell

Published: Wednesday, 09 March 2022 at 12:00 am

This goofy little animal is an inhabitant of Mexico, and its name comes from the Aztec god of fire and lightning, Xolotl. According to the stories, Xolotl transformed himself into an axolotl in order to avoid being sacrificed. While his ruse didn’t work and he was eventually slain, the axolotl continues to be an iconic animal that has fascinated humans for centuries. The amphibian defies biological laws like metamorphosis, and can even regenerate lost body parts, making it an important research subject in labs around the world.

The axolotl is a species of salamander. Salamanders are a type of amphibian, which is the group that also includes newts, frogs and toads.

Amphibians need water to reproduce (although there are a handful of species that have evolved some ingenious methods to get around this). They’ll lay their eggs in water, and then larvae will hatch out and gradually metamorphose into the adult form, which can live on the land.

Axolotls, however, never really grow up. They are ‘neotenous’, which means that – unlike most amphibians – they do not metamorphose into lung-breathing, land-living adults. Instead, they retain juvenile features such as gills, tails and a preference for living in water.

What do axolotls look like?

With their bald heads, button eyes and gummy smiles, axolotls are undeniably cute… and weird.

Adult axolotls measure about 30cm in length, from the tip of their nose to the end of the tail, with the biggest individuals achieving up to 45cm in length. They can tip the scales at around 300 grams.

Aside from their chunky bodies and comically short limbs, they sport some seriously outrageous headgear in the shape of six feathery gills that frame their adorable baby faces. Those gills – which can also be seen in other species of young amphibians – allow them to extract oxygen from the water, so they can breathe. Along with their gills, axolotls have very reduced lungs, and they are occasionally seen taking little gulps of air at the surface.

Where do axolotls live?

The axolotl is native only to Mexico City’s Lake Xochimilco. This is a high-altitude region with a water temperature that rarely rises above 20°C. They used to live in Lake Chalco as well, but this was drained in the 1970s to prevent flooding. Their numbers are decreasing due to pollution and the expansion of Mexico City encroaching upon their habitat. As a further blow, introduced freshwater fish eat the axolotl eggs and its preferred insect prey.

Are axolotls endangered?

The IUCN Red List of Threatened Species lists axolotls as critically endangered. According to a paper published BioScience in 2015, axolotls have experienced a catastrophic collapse over the past couple of decades. In 1998, researcher Dr Luis Zambrano González counted 6,000 axolotls per square kilometre. By 2008, just 100 of the amphibians were found per square kilometre. More recent data suggests there are fewer than 36 per square kilometre.

Meanwhile, captive populations are thriving in labs around the world, and the endearing amphibians also make popular pets. In recent years, millions of gamers have got to know these animals after they were introduced as playable characters in Fortnite in 2020. The following year, the axolotls popped up in the lush caves biome of Minecraft.

How can we save the axolotls?

“The first consideration is that we cannot save the wild axolotls without restoring their habitat. Therefore, to protect the axolotls in the wild – before thinking about reintroductions – it is necessary to restore the wetland. All the attempts to introduce axolotls failed because of that,” says Zambrano González. “We are working on restoring the habitat, which is intrinsically linked with the pre-Columbian culture. For that reason and others – such as reducing genetic diversity and introducing axolotl diseases – it is not advisable to generate a programme of captive-bred reintroduction.”

According to research carried out by Zambrano González and others, the crucial first step in developing refuges for the axolotls is improving water quality. This change would be beneficial to native species like the axolotl, but would also be better for the crops, making it an attractive option for farmers.

Read more about amphibians:

Why are scientists interested in axolotls?

These weird animals have fascinated scientists since they were first brought to Paris from Mexico in 1863. Researchers have found that the animals have an extraordinary ability to regrow whole limbs, eyes, heart tissue, bits of brain, and segments of spinal cord when injured, restoring the body parts to full functionality. They will even readily accept transplanted limbs from other individuals.

It is possible to induce an axolotl to undergo metamorphosis by exposing it to thyroid hormones. However, this will hinder the animal’s ability to regenerate, and may also affect its microbiome, according to research published in the journal Scientific Reports in 2018.

A study published in Nature sequenced the genome of the axolotl to 32 billion base pairs – 10 times bigger than the human genome. At the time, it was the largest genome of any animal, but it has since been overtaken by the lungfish with 43 billion base pairs. Its genome revealed specific sequences that may be responsible for limb regeneration.

What do axolotls eat?

Axolotls will eat pretty much anything they can fit into their mouth! In the wild, their diet includes worms, freshwater insects, crustaceans and small fish. They are also cannibalistic animals, and will take bites out of each other if there is not enough food available.

Axolotls kept as pets or in the lab will be fed worms, shrimp or bits of fish. As the animals have undeveloped teeth, they go for the ‘vacuum’ method of feeding, sucking anything small enough into their mouths.