Rebuilt from the inside
How Does a Caterpillar Become a Butterfly?
Inside the chrysalis the caterpillar is largely dissolved and reassembled.
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Step 1 of 5
The caterpillar's only job is eating.
It is a feeding machine with strong jaws, and can grow thousands of times its hatching weight in a few weeks.
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Step 2 of 5
Then it seals itself away.
It attaches to a stem and forms a hard case. It cannot eat, cannot flee, and cannot change its mind — it is entirely committed.
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Step 3 of 5
Most of the body is dissolved.
It does not rearrange itself. It takes itself apart and starts again. Enzymes break the caterpillar down into a soup of cells and nutrients. Almost nothing of its old structure survives intact.
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Step 4 of 5
Special cell clusters build the new body.
Groups of cells present since hatching, called imaginal discs, use that soup as raw material to build wings, legs and eyes.
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Step 5 of 5
Some memory survives the rebuild.
Experiments show butterflies can still avoid a smell they were trained to dislike as caterpillars — so parts of the nervous system persist.
A freshly emerged butterfly must pump fluid into its crumpled wings and wait for them to harden before it can fly.
The short version
The caterpillar dissolves itself into a soup of cells, and clusters called imaginal discs — present since it hatched — build a butterfly out of the wreckage. Some of its trained memories survive the process.
Try it yourself
Raise a caterpillar in a ventilated jar with fresh leaves. The chrysalis darkens a day before the butterfly emerges.