From
Caterpillar to Chrysalis
Contributed by Dr. Lincoln Brower
Dr. Brower explains: why does the monarch twist and turn so vigorously as the chrysalis forms?
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1) Look at that little black post at the top under a microscope you'd see dozens of beautiful little hooks. As the chrysalid twists, this black post with barbed hooks are getting into the silk. If that little post doesn't get into the silk then the chrysalid will fall to the ground. And if it falls to the ground it will kill the chrysalid because at this stage the chrysalid is incredibly delicate and--it's really just almost a bag of fluid.
2) The second thing that is happening is that — if you watch (the video clip) really carefully — you'll see the larval skin — which now looks almost like a fly that slid up and up and up and up. The chrysalid has to get rid of that because if it doesn't it will stick to the surface and that will deform the butterfly. The butterfly would not be able to get out of its chrysalid unless it gets rid of its skin which messes up the metamorphosis process.
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Scanning
electromicrograph showing the tip of the cremaster post of a monarch
butterfly chrysalid embedded in the silk pad. |
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© Dr. Lincoln Brower, Sweet Briar College. All Rights Reserved. |
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More About the Process
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The 5th instar
larva spins the silk pad. Then it grabs the silk pad with curved hooks
on its two hind prolegs. (The curved larval hooks on the prolegs are NOT
the barbed hooks pictured here.) The caterpillar can then turn around
and hang upside down, split and wriggle its skin up, dislodge the larval
hooks, and then cast off the little rumpled larval skin (the skin flick).
However, the newly formed chrysalid would fall to the ground if it did
not have the cremaster post with its barbed hooks to thrust into the silk.
It embeds the cremasters' barbs by the twisting motion of the abdomen
and the cremaster post. Once the cremaster's barbs are safely into the
silk pad, ONLY then can it pull out the unbarbed larval hooks and toss
off the old larval skin...
For a moment it's suspended-for a split second it's not connected to anything.
(Like transferring a rope between your leg and stomach in mid air.) Somebody
needs to do high speed photography and really look at this moment because
nobody really knows how they do it.
Once the cremaster hooks are embedded, they cannot be dislodged...because
of the barbs. When the adult hatches out of the chrysalid, it leaves the
chrysalid behind, still attached to the silk pad.
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Audio Clip Hear
Dr. Brower Explain |
National Science Education Standards
Science as Inquiry
- Simple instruments, such as magnifiers, thermometers, and rulers, provide more information than scientists obtain using only their senses. (K-4)
Life Science
- Each plant or animal has different structures that serve different functions in growth, survival, reproduction. (K-4)
- Living systems at all levels of organization demonstrate the complementary nature of structure and function. (5-8)
- Plants and animals have life cycles that include being born, developing into adults, reproducing, and eventually dying. The details of this life cycle are different for different organisms. (K-4)
Science
and Technology
Tools help scientists make better observations, measurements, and equipment
for investigations. They help scientists see, measure, and do things that
they could not otherwise see, measure, and do. (K-4)
