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Hometown Field Guidesby Garden with Lilly

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Plate 3

The chrysalis, outside and inside

On the right, the same chrysalis opened up, as a diagram, in its first days and in the middle, then whole on the last day, when the wings show through the case. It hangs head-end down, so the butterfly's head forms at the bottom.

Watercolor of a jade-green monarch chrysalis hanging by a black stalk from a silk pad under a leaf, with a band of gold dots and the outlines of the folded wing, the leg and tongue cases and the eye bump. Beside it, the same chrysalis at three ages: cut open on its first days, full of soft pale tissue threaded with air tubes; cut open in the middle, with the new wing, legs, tongue, eye and body taking shape; and on the last day, whole, with the orange and black wings showing through the case.
  1. Silk padBefore changing, the caterpillar spins a little silk mat, grabs it with its back legs and hangs upside down in a J.
  2. Hook stalkA black stalk at the top, tipped with tiny hooks, holds on to the silk like Velcro.
  3. Chrysalis skinA chrysalis isn't spun or built. It's the caterpillar's own new skin, which hardens into a green case.
  4. Gold bandThe gold isn't real gold. Stacks of see-through layers bounce light like a soap bubble. Nobody knows for sure why it's there.
  5. Folded wingThis big smooth patch is a folded wing. The wings are already there, pressed flat under the skin.
  6. Leg, tongue and antenna casesThin ridges show where the antennae, tongue and legs lie folded, like clothes packed in a suitcase.
  7. Eye bumpNear the bottom, a smooth bump shows where the big butterfly eyes are forming.
  8. First days: breaking downInside, many caterpillar parts break down into a soft, gooey mix. But it isn't all liquid.
  9. Air tubes, keptMany of the air tubes are already there. In painted lady chrysalises, X-ray scans showed them about 12 hours after the chrysalis formed.
  10. Middle: buildingStarter cells use that gooey food to build new parts: wings, long legs, big eyes and a two-part tongue. The two halves zip together after the butterfly comes out.
  11. Last day: the wings showA day before the butterfly comes out, you can see its orange and black wings through the case. The case hasn't changed; the wings have just got their color.

What happens next

  • The butterfly pushes out, hangs from the empty case and pumps fluid into its crumpled wings to stretch them.
  • It drips a little liquid called meconium. That isn't blood. It's waste saved up inside the chrysalis.
  • Parts of the nervous system are kept and rewired. Moths can even remember a smell they learned as caterpillars.
  • A chrysalis is not a cocoon. Many moths spin cocoons; a butterfly's chrysalis is its own skin.

Sources: Monarch Joint Venture; Monarch Watch; Lowe et al., J. R. Soc. Interface (2013) on X-ray scans of painted lady chrysalises; Blackiston et al., PLoS ONE (2008) on memory through metamorphosis. The "it all turns to liquid" line in some popular articles is a myth.

Don’t rely on a drawing alone to identify a living thing or to decide whether it is safe to touch.

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