monarch butterfly pupa / chrysalis
The pupa, or chrysalis stage of metamorphosis is the one which will define the future of this insect more than any other. From here we see the total transformation of the larva, a yellow, black and white-striped caterpillar, as it moves from being earth-bound with sixteen feet to being able to fly thousands of miles on four wings.
From the time the caterpillar sheds its last skin (the 5th instar), it takes nine to eleven days (or longer if it's cold out) for the butterfly to develop inside the chrysalis. (Because monarchs are insects they're cold-blooded and their development is dictated by temperature, as is their ability to fly, etc.)
The word chrysalis is derived from the Greek word 'crusoz' meaning gold.
Within the pupal case, most of the the caterpillar body breaks down through a process called histolysis. Special groups of transformative cells, which remained hidden and inert during the larval stage, now become the directors of the body's reconstruction. These cell groups, called histoblasts, initiate biochemical processes which transform the deconstructed caterpillar into a viable butterfly or moth. This process is called histogenesis, from the Latin words histo, meaning tissue, and genesis, meaning origin or beginning.
Once the metamorphosis within the pupal case is completed, the butterfly or moth may remain at rest until the appropriate trigger signals the time to emerge. Changes in light or temperature, chemical signals, or even hormonal triggers may initiate the adult's emergence from the chrysalis.
If you've ever raised monarchs you might have observed that they usually emerge after dawn if consistently exposed to natural light, like by a window, or if the light in their environment is kept on a consistent schedule that follows natural light patterns. If it's not you may have butterflies emerging at all times of day and night.
an upside-down butterfly develops
The photo above shows what happens as the chrysalis turns clear within hours of the butterfly eclosing, or emerging. It turns from the beautiful jade green to completely clear and you can easily see the wings, etc. You can also see the difference between the male and female by the thickness of the black vein lines on the wings. The male's (3rd from left) are thin and defined, and the female's (4th from left) are thicker. (Also, you can see the way I attach monarchs so I can pin them to the top or side of a cage to emerge. I scrape the silk off the top of a container - I use a sharp, pointed pair of medical tweezers - and then just tape it, along with the top of the cremaster, to a small piece of paper towel. Some people use hot glue guns to attach them to sticks.)
In the photo on the left you can see lots of detail inside the chrysalis. (Keep in mind that monarchs develop upside down, so the head is at the bottom.) The abdomen at the top, then the wings are on both sides. Right down the middle between the wings are the antennae and the tongue, also called the proboscis, which develops completely flat and split in two. It's only after the butterfly emerges that it will join the two sides of its proboscis together and curl it up by its head. At the bottom, beneath the gold dots, are the butterfly's complex eyes.
Their white scales can been seen fairly well on the abdomen at the top. Monarchs are covered with thousands, or millions, of scales all over except for the surface of their eyes.
When a monarch emerges from its chrysalis it will push it open with its feet. The chrysalis will split along the lines of the two antennae and then it will pull itself out and then hang while pumping up its wings with the fluid stored in its abdomen.
It's impossible to look at a monarch chrysalis and not see what looks to be gold on the line at the top and gold dots along the bottom. There are a couple of theories that I've read relating to the purpose of this "gold"; one being that the reflection it creates scares away predators, and the other being that the gold determines the color of the wing scales beneath it, a finding born out of research by Dr. Fred Urquhart from the U. of Toronto.
The cells reflect light like metals do giving the appearance of gold, so while it looks like metallic, it is not.
attaching the chrysalis
If you've ever wondered how a monarch butterfly chrysalis adheres to the silk button it spins, you can see from this photo of the cremaster (black appendage at the top of the chrysalis) that there are many little hooks and they act like velcro when pushed into the silk. Sometimes the chrysalis will fall but most of the time it's a very secure connection that can withstand storms, etc.
I often save some of the silk I scrape off the top of the containers, so if a chrysalis does fall it's easy to push a little silk into the cremaster, which enables me to then hang it elsewhere. I usually tape the silk and cremaster to a small square of paper towel that can be easily pinned inside a cage.
it's a GIRL!
You'll probably need a magnifying glass, but you can tell the sex of a monarch butterfly while it's still in its chrysalis. A female monarch will have a very tiny vertical line just beneath the black cremaster on the "wing side" of the chrysalis, which is the side opposite of the gold line as seen above. If there's not a vertical line as seen on the right, it'll be a male monarch. I once read that it was an eleven-year-old boy who discovered that distinguishing feature!