Saturday, August 21, 2010

Monarch Cremaster SEM

Every year, millions of Monarch caterpillars change into chrysalises.  During this change, the caterpillar literally sheds its skin and becomes a chrysalis.  As it slips out of its skin, it must let go with its legs and hold on with its cremaster, the black stem at the top of the chrysalis.

The two lowest black dots of a Monarch chrysalis are called 'holdfast tubercles'.   A pupating caterpillar/chrysalis is literally suspended by two tiny holdfast tubercles for a moment as it withdraws its cremaster from underneath its old skin and grasps its silk button with the tip of its cremaster.  Long ago scientists discovered that the tip of the cremaster is covered with tiny hooks.  These hooks become tangles with the loops of the silk pad it had made before pupating.
This step is critical.  If the cremaster doesn't grasp the silk button and falls onto most surfaces, it ruptures.  The chrysalis breaks open upon impact with the surface below it.  We still often hold our breath as we watch this critical moment during pupation ... STRESS ... will it make the reach?  Will someone bump the table?  Will wind blow at the wrong time?  Will an animal pass by and knock it off the stem before it finishes? 

We were given Scanning Electron Microscope (SEM) images of the tip of a Monarch cremaster, along with permission to use the images.  This is an image of a Monarch cremaster with its hooks locked into the loops of its silk button.  No wonder it holds so well! 

The cremaster's hooks and silk pad's loops are much like Velcro®.  Unlike  Velcro®, the hooks and loops make a connection so tight that if one simply pulls at the chrysalis, the chrysalis will break before the hooks pull loose from the silk pad. This protects the cremaster from being blown loose in storms. 

It is good to be reminded again that God was there first.  He created everything.   How wonderful it is to rest in the knowledge that such a God is still here, handling things from year to year, month to month, week to week, day to day, hour to hour, minute to minute, and even second to second.  What a stress relief!

Genesis 1: 20-25
And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven. And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good. And God blessed them, saying, Be fruitful, and multiply, and fill the waters in the seas, and let fowl multiply in the earth. And the evening and the morning were the fifth day.

And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earth after his kind: and it was so. And God made the beast of the earth after his kind, and cattle after their kind, and every thing that creepeth upon the earth after his kind: and God saw that it was good.