Caterpillar to Chrysalis
Contributed by Dr. Lincoln Brower
explains: why does the monarch twist and turn so vigorously as the chrysalis
This is a
really critical stage in the life history of the monarch because this
is truly when the caterpillar has just become a chrysalid and it has just
shed its skin. There are two things that are happening when it twists:
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.
caterpillar spins a silk pad. When it transforms into a chrysalis,
barbed hooks hold strands of the silk so the chrysalid won't fall
to the ground.
electromicrograph showing the tip of the cremaster post of a monarch
butterfly chrysalid embedded in the silk pad.
© Dr. Lincoln Brower, Sweet Briar College. All Rights Reserved.
More About the Process
caterpillar's shed skin looks like a fly.
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.
file 192 Kb)
for the caterpillar's skin to fall away from the chrysalis
Dr. Brower Explain
file, 15 Mb)
file, 1.4 Mb)
Science Education Standards
instruments, such as magnifiers, thermometers, and rulers, provide more
information than scientists obtain using only their senses. (K-4)
- Each plant
or animal has different structures that serve different functions in
growth, survival, reproduction. (K-4)
systems at all levels of organization demonstrate the complementary
nature of structure and function. (5-8)
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)
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)