What’s inside a caterpillar cocoon

  • Contrary to popular belief, a chrysalis is not a pouch or a sac with a caterpillar inside. It’s actually the caterpillar’s own body!
  • During metamorphosis, the former caterpillar releases digestive juices that rip apart and dissolve cells in its muscles, digestive system, and other organs. 
  • Then, special groups of cells called imaginal discs divide over and over again, forming wings, eyes, and adult structures.
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Following is a transcript of the video.

What would you do for the power to fly? How about shedding your skin and dissolving your own muscles? Now, believe it or not, that gruesome process is how caterpillars earn their wings. Here’s what you might not know about what’s inside a caterpillar’s “cocoon.”

Contrary to popular belief, this is not a cocoon. Only certain moths build cocoons, which are like a silky sleeping bag that covers the insect. This, on the other hand, is what’s called a chrysalis. It’s not a sack or a pouch; it’s actually the caterpillar’s own body.

When it’s time for the transformation to begin, the caterpillar’s body ramps up production of a hormone called ecdysone, and that causes it to cast off its outer coating, sort of like how a snake sheds its skin. And underneath is a hard shell similar to the exoskeleton of a beetle.

After that, life for the little caterpillar gets oozy. First, it releases enzymes called caspases. These rip apart and dissolve cells in its muscles, digestive system, and other organs. But the enzymes don’t quite liquefy all of the caterpillar. They leave key structures intact, like breathing tubes. At the same time, specialized cells called imaginal discs start waking up.

Before the chrysalis stage, these discs were kept dormant by a series of hormones in the caterpillar’s body. But once the transformation begins, those hormone levels take a nosedive, giving these discs the opportunity to do what they do best: build a butterfly. You see, each disc contains the genetic recipe to form a different adult body part, starting from the inside out.

After one week, the digestive system of the butterfly is well on its way. And by day 16, the adult’s legs, wings, eyes, and mouth are all present and in working order. Now, two weeks is a remarkably short time for all of this to happen, since each imaginal disc starts out with only about 50 cells and must multiply those into thousands just to form a single wing.

And if you checked out the chrysalis around day 16, you might even be able to see those brilliantly colored wings. Because for some species, their chrysalis turns transparent in their final days of metamorphosis.

Now, fully formed, it’s time to hit the road. The chrysalis splits open down the center, and the butterfly escapes. Meanwhile, a reddish liquid spills out. That’s all the waste the butterfly, née caterpillar, produced during its stay. Once its wings expand and harden, it’s ready to mate, pollinate, and slurp nectar to its heart’s desire.

But one of the most interesting parts of all? Research suggests that butterflies and moths can remember their caterpillar days. In one study, researchers trained moth caterpillars to associate an odor with an electric shock, so whenever the larvae smelled it, they’d move away. But even after they transformed into adult moths, they still avoided the scary smell. It makes you wonder what else they could recall from their younger days.

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