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How does a caterpillar change into a butterfly​?

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📓 The short answer

Caterpillars turn into butterflies by digesting their bodies inside a chrysalis and rebuilding them into butterfly parts by using special cells called imaginal discs.

📚 The long answer

If you thought puberty was rough, count your blessings you didn't go through a complete metamorphosis.

Butterflies are among the many animals that go through their lives in two distinct bodies. Early in life they walk around as caterpillars munching on plants. Then after a full-body rebuild inside a chrysalis, they emerge as flying nectar-drinkers.

Welcome to the wild world of butterfly metamorphosis. Let's dive into the details of how this mega-puberty works:

🥚 Stage 1: Egg

A butterfly's life begins when its mother lays eggs on a plant, often on the underside of a leaf to avoid detection by predators. That plant will become the caterpillar's second meal — its first will be its own eggshell.

These tiny eggs will develop not only the parts needed to be a caterpillar but also later a butterfly. They grow "imaginal discs," clusters of cells that later form adult body parts like wings, antennae, and legs. The journey to a butterfly starts at inception.

🐛 Stage 2: Larva (caterpillar)

After hatching from its egg, the butterfly is in its larva, or caterpillar, stage. It now has one job and one job only: EAT.

For the next few weeks, the caterpillar devours leaves to fuel its rapid growth. As it grows plumper, it will molt (shed its skin) several times to transform into a larger version of itself. Some species of butterfly will end up being 100 times larger than when it started.

Eating can also be a defensive mechanism. Some caterpillars will intentionally eat plants that contain toxins, making them poisonous to other predators even after they've transformed into butterflies.

🛡️ Stage 3: Chrysalis

It's "The Final Molt-down" for the butterfly as it molts for the last time to form a shiny, hard chrysalis that protects against extreme temperatures, parasites, and moisture loss.

Now the fun part begins: How do you transform all those caterpillar parts into butterfly parts? You liquefy yourself, of course!

The caterpillar will digest itself, releasing enzymes that dissolve most of its tissues. It's often said that the chrysalis will contain a "soup" of caterpillar parts, but it's probably more accurate to call it a "stew" because not all of its body parts dissolve.

Crucially, the imaginal discs survive this digestion process and use this protein-rich broth to fuel the rapid growth of wings, antennae, legs, eyes, and other butterfly features.

As butterfly parts grow (like the wing vein structure, shown in blue above), some parts get smaller (like the digestive system, shown in red) since butterflies will change their eating habits from fibrous plants to simple nectar. This process of transforming from a caterpillar to a butterfly will take about 2-4 weeks to complete.

🦋 Stage 4: Butterfly

The adult butterfly will emerge from its chrysalis with the help of a hormone that provides the strength needed to bust out. It's a little less dramatic than how the Metapod evolves into a Butterfree in Pokémon, but it's still an amazing process.

And after being folded up for several weeks, the butterfly's wings need to stretch out. It pumps a blood-like substance called hemolymph into its wings so they can expand and harden for flight.

Now the adult butterfly has a new job: make more butterflies. A butterfly will court mates with scents and elaborate aerial dances. Some butterflies lay their eggs close to where they were born, but others, like the Monarch butterfly will embark on continent-spanning migrations to lay their eggs on the other side of the world. Then the cycle will begin again.

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

🌐 Wikipedia article of the week

​Telling the bees​

"Telling the bees is a Western European tradition in which bees are told of important events, including deaths, births, marriages and departures and returns in the keeper's household....After the death of Queen Elizabeth II in 2022, the Royal Beekeeper, John Chapple, informed the bees of Buckingham Palace and Clarence House of her passing and the accession of King Charles III."

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👀 Catch up on other curious questions

• ​What happens to an insect that hitches a ride far from their home?​​
• ​Why do dogs stick their head out the window?​​
• ​Are there more people alive today than have ever lived?​​

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