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A Path from the app

What an axolotl actually is.

This is the Path that every Gillo account starts with: 16 short lessons on the axolotl, in four units. After it you can say what the animal is, how it regrows a limb with no scar, where the last wild ones live, and why laboratories keep it.

Units
4
Bites
16
Lesson time
83 min
Price
Free

By the Gillo team · Last updated November 10, 2026

Who it is for

A parent who wants to keep up with a child that loves axolotls. No biology is assumed.

Built from field surveys, keeper guides and the regeneration literature.

Unit 1 of 4

What it is

A salamander that never grows up: gills, lungs, neoteny

  1. 1. A salamander that refused to grow up · 5 min · 5 questions

    • An axolotl is a salamander that never finishes growing up.
    • Pink means captive-bred. Wild axolotls are dark and mottled.

  2. 2. Gills, lungs and a third option · 5 min · 4 questions

    • The frills are gills. It also has lungs, and it breathes through its skin.
    • Curled gills mean stress. Fluffy gills mean the water is right.

  3. 3. Can it grow up? Only if you push it · 5 min · 4 questions

    • Thyroid hormone makes an axolotl grow up. On its own, it stays a kid.
    • Staying in the water worked while the lake was good. Then the lake changed.

  4. 4. Water monster: the name and the numbers · 5 min · 4 questions

    • Axolotl is Nahuatl for “water monster”. The god Xolotl hid as one.
    • Millions in tanks. A few hundred, at most, in the wild.

Unit 2 of 4

Regrowth

The blastema, what grows back, why there's no scar

  1. 5. It doesn't scar. It rebuilds · 6 min · 4 questions

    • Other animals seal the wound. An axolotl regrows the part.
    • Legs, tail, jaw, spinal cord, heart and brain can regrow. The animal can't.

  2. 6. Inside the bud · 6 min · 4 questions

    • Cells step back, divide, and rebuild. Without a nerve, nothing grows.
    • Cells know where they are, so they rebuild only what's missing.

  3. 7. Age, limits and the scar question · 6 min · 4 questions

    • Regrowth fades with age but never stops, as long as it stays larval.
    • A thin skin roof instead of a scar is what lets the bud form.

  4. 8. Why it matters to us · 5 min · 4 questions

    • We have the same genes. The question is what turns ours off.
    • Regrows parts, not itself. Keeps the trick by staying a kid.

Unit 3 of 4

Where it lives

Xochimilco, cold clean water, and what is killing it

  1. 9. One lake inside a megacity · 5 min

  2. 10. Cold, clean and dark · 5 min

  3. 11. The invaders: carp and tilapia · 5 min

  4. 12. Chinampas and the comeback plan · 5 min

Gillo writes the Bites of this unit when you reach it, so only the titles are here.

Unit 4 of 4

Why scientists love it

A century in the lab and a genome ten times ours

  1. 13. A century in the lab · 5 min

  2. 14. 32 billion letters · 5 min

  3. 15. The regeneration map · 5 min

  4. 16. What it could mean for us · 5 min

Gillo writes the Bites of this unit when you reach it, so only the titles are here.

The first Bite, in full.

This is what you read in Bite 1, “A salamander that refused to grow up”. In the app, Gill reads it to you, and questions come between the parts.

It's a salamander that refused to grow up.

An axolotl is a salamander. Most salamanders start life in the water with feathery gills, then lose them, grow lungs and move onto land.

An axolotl skips that part. It keeps its gills, stays in the water and keeps its larval body for its whole life. Biologists call this neoteny.

In the wild it lives in one place: the canals of Lake Xochimilco in Mexico City, where it is critically endangered.

Nearly every axolotl alive today lives in a lab, an aquarium or someone's living room. The pink ones you see online are a captive-bred color. Wild ones are dark and mottled.

The one line to keepAn axolotl is a salamander that never finishes growing up.

Pink is a pet-shop color.

Wild axolotls are dark: brown, olive, mottled with gold flecks, which is good camouflage on a muddy canal floor. The pale pink animal with red gills is a leucistic form, bred in captivity for over a century. It is not an albino. Its eyes are dark.

There are others: white albinos with red eyes, golden albinos, and a dark melanoid with no shine at all. Every one of them is the same species. Color tells you where the animal came from, not what it is.

The one line to keepPink means captive-bred. Wild axolotls are dark and mottled.

Questions people ask.

Is this course free?

Yes. This Path comes with the app on every plan, Free included, and it does not count as one of your new Paths for the month.

How long does the course take?

It has 16 Bites of 5 to 6 minutes, so the lessons are about 85 minutes in all. Each unit ends with a check, and the Path ends with a capstone that you pass at 80 percent.

Do I need to know biology?

No. It is written for a beginner. Each new word, such as neoteny or blastema, is explained when it first appears and then comes back in the questions.

Why are the last two units not shown in full?

The first two units are written by hand and are the same for everyone. Gillo writes the Bites of units 3 and 4 when you reach them, so this page shows their titles only.

Can I get a course like this on another topic?

Yes. That is what Gillo does. You type a topic or bring a document, and Gillo builds a Path in the same shape: four units, 16 Bites, checks and a capstone.

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