How The !@#% Does It Do That?
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The other day I came across some caterpillars. These were the larval form of a Pipevine Swallowtail Butterfly. They were well-advanced in their development, being nearly three inches long and every bit as thick as my index finger. Soon, these caterpillars would make the transition to adulthood.
How do they do it? We all know that caterpillars eventually form a sort of cocoon (chrysalis) and that a process goes on inside that transforms them into adults. But, what’s going on in there? I did a little research and the truth, as it turns out, is as fascinating and downright weird as anything I could have imagined. The following story is courtesy of a Scientific American article from 2012.
Butterfly eggs develop little clumps of cells called “imaginal discs” that contain all of the genetic material necessary to form adult organs. There are discs for wings, eyes, legs, internal organs, etc., and each of them is only a few cells in size. When the eggs hatch and the tiny caterpillars emerge, they carry the imaginal discs embedded in their bodies. Those discs stay there through the growth of the caterpillar, basically waiting for the right time. Meanwhile, the caterpillar, which is basically a walking digestive tract, eats and eats, grows and grows. But, the discs for the most part remain dormant, just tiny packages of genetic material embedded in the caterpillar’s body.
At some point the caterpillar acquires enough raw material to supply the energy needed to make the transformation to adulthood. It secretes a chrysalis and the transition begins.
And, the caterpillar dissolves! That’s right, it turns into a fat and protein soup, essentially liquid nutrient. And, from this, the embedded imaginal discs, which don’t dissolve, obtain the energy to build and assemble adult body parts. So the chrysalis is basically a butterfly factory inside of which the imaginal discs cannibalize the body tissues of the caterpillar in order to construct a butterfly. A butterfly is not a modified caterpillar. It is an entirely new organism built out of the caterpillar’s body tissues.
Now, how cool is that?
Pictures taken with a Canon 5Diii, 180 f3.5L Macro Lens, assisted by Canon 600EX-RT Speedlite, ISO 100, “M” setting, f8 @ 1/100.