More About the Process

The 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.

Video Clip

Monarch Metamorphosis

.mpg file 192 Kb)

Watch for the caterpillar's skin to fall away from the chrysalis

Audio Clip

Hear Dr. Brower Explain

(.wma file, 15 Mb)
.wav file, 1.4 Mb)

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)