Axolotl

The axolotl is a salamander that decided childhood was working out fine and stuck with it. It spends its whole life underwater wearing the feathery gills most amphibians lose in weeks, it can regrow almost any body part it loses, and it exists in the wild in just one place on Earth — a network of canals in Mexico City.

Overview

Axolotls are a type of mole salamander. Their relatives dig burrows on land as adults; the axolotl never leaves the water. It evolved in the cool, deep, permanent lakes of the Valley of Mexico, where staying aquatic was safer than crawling out onto dry, high-altitude land — so natural selection favoured animals that skipped metamorphosis entirely. This trait is called neoteny or paedomorphosis: keeping juvenile features into adulthood.

Physical characteristics

An axolotl has a broad head, a wide mouth fixed in what looks like a permanent smile, tiny lidless eyes, four short legs, and a long finned tail. The showpiece is the set of three feathery external gill stalks on each side of the head, richly supplied with blood, which the animal waves to move fresh water over them.

Wild axolotls are dark brown or greenish with speckles — good camouflage in muddy water. The pale pink and white axolotls everyone recognises are captive colour morphs (leucistic and albino) that would not last long in the wild.

Regeneration

The axolotl’s most famous trait is its ability to regenerate. Lose a leg and it grows back completely — bones, muscles, nerves, blood vessels, skin — in a matter of weeks, with no scar tissue, and it can do this over and over. It can also repair or rebuild parts of the heart, the jaw, the retina, the tail, and even sections of the spinal cord and brain.

How it does this — reactivating a wound site into a bud of stem-like cells that rebuild exactly what was there — is one of the biggest questions in regenerative medicine, which is why axolotls are bred by the tens of thousands in research labs.

Diet and behaviour

Axolotls are ambush carnivores. They lie still on the bottom and, when a worm, insect larva, small fish, or crustacean comes close, snap the mouth open to create a vacuum that sucks the prey in — a feeding method called suction feeding. They have small teeth for gripping but swallow food whole. Adults are largely solitary and will bite at the limbs and gills of other axolotls, which, conveniently, grow back.

Reproduction and life cycle

Breeding is triggered by cooling water and lengthening days. In a courtship “waltz,” the male deposits small cones of sperm on the lake bed and leads the female over them to pick them up. She then lays 100 to 1,000 jelly-coated eggs, attaching them singly to plants and rocks. The larvae hatch after about two weeks looking like miniature adults and are independent immediately. They never metamorphose; they simply grow.

Threats and conservation

The axolotl is Critically Endangered in the wild:

• Habitat destruction. Mexico City has grown over and drained the ancient lake system; only the canals of Xochimilco remain, and they are shrinking.
• Pollution. Untreated wastewater and agricultural runoff have degraded water quality across the canals.
• Invasive fish. Tilapia and carp, introduced for food, eat axolotl eggs and young and compete for prey.

Conservation efforts focus on Xochimilco itself — creating clean, filtered, predator-free “refuge” channels maintained with traditional chinampa farming, and reintroducing captive-bred axolotls — alongside the vast insurance population living in aquariums and labs around the world.