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?

Listen to Dr. Brower

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.

The 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.
Scanning electromicrograph showing the tip of the cremaster post of a monarch butterfly chrysalid embedded in the silk pad.
Images © Dr. Lincoln Brower, Sweet Briar College. All Rights Reserved.

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)