Naturespeak A naturalist's view of the world

June 30, 2008

A Miraculous Transformation

Filed under: Uncategorized — wykes @ 9:13 pm

In the backwards world of blog posts, that which comes after precedes that which comes first. So, when I say this post is part two of our examination of baby Black Swallowtail Butterflies you’ll need to scroll down in order to review part one (“Stepp’n Out and Stink’n Up”).  In the real world, that which comes before precedes that which comes after. Caterpillars eat, grow, and eventually transform into adults.  This is the natural order of things.  Come to think of it, people do the same thing (except we go through a couch potato stage instead of a pupal stage).

  It should be no surprise, then, when I tell you that the larvae we looked at a few days ago have now taken the next big step in their brief careers. They have transformed themselves into the third metamorphic stage known as the chrysalis. 

  No matter how you look at it, this is the beginning of one of nature’s true miracles. Upon reaching their maximum size (which takes about 10 days), the caterpillars say good-bye to their Parsley eating days. They begin to wander about and look for a suitable spot to perform their miracle. In the confines of their small container home, my captives put in a mile of laps as they went around and around the perimeter. In the wild, caterpillars seek a location as far from their food plant as they can get.

  Miracle workers need to choose their spots carefully. A slanting horizontal surface is considered a prime spot – especially if it is under shelter and secreted away from the prying eyes of predators. The larvae weave a silk pad, once they are satisfied with their site selection, and advance forward to the point where they can hook their back feet firmly into the silk.

  A silken support is then woven into place like a lineman’s harness. Multiple threads are repeatedly glued to the surface, brought around behind the head, and then looped around the thorax.  After this step, the larva leans back and allows the harness to support his weight (see above).

  It takes the better part of a day and a night for it to happen, but the final act in this scenario is one where the skin on the back of the caterpillar splits open. The old skin is worked off via a series of gyrations as the newly formed chrysalid creature is slowly revealed. That chrysalis is a reformation of the caterpillar’s body -sans legs. The bright green chrysalis takes on a sleek streamlined look after an hour or two (see here).

  Inside this new hard shelled package, the larva is essentially dissolving into mush. The body is breaking down into simple cells called marginal cells. Body cells revert into simple un-committed entities -similar to stem cells -that can be reassigned to become wings, antennae, and long tubular tongues.

  The root word for chrysalis means “gold” in the ancient Greek tongue. This is an appropriate name if you consider that the chrysalis is like a precious goblet that holds the promise of a new lifestyle. In about a week and a half the miraculous transformation will be complete as the swallow-tailed adult emerges from its green-gold chalice.



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