Thursday, March 14, 2019

Winter Chrysalis

Sharon Hughes gave me this pupa at our Master Naturalist meeting on Monday.  Her husband found it hanging from the top of the door frame between the screen door and the front door. It looked like a butterfly chrysalis including a telltale string of silk with which it had suspended itself, waiting to spread its wings with the help of gravity.  Alas, winter had caught it and literally frozen it in time.

Kevin Firth identified it before the ink dried on my email request.  This is a spicebush swallowtail chrysalis, characterized by the two diagnostic anterior 'horns'.  We discussed the caterpillars in last June's blog.      The photographs below from the University of Florida will show how the chrysalis is suspended in nature.  The picture, on the bottom left, gives a better idea of where the wings will emerge and you can even make out the spiracles.

Photo by Donald Hall

Photo by Donald Hall

Since this had been found on a door jam outside of the front door, I had little hope that it would survive the freezing temperatures.  Just in case, I kept it in a bug box to watch.  One afternoon as I walked by the kitchen counter (my wife is a saint) I saw something move out of the corner of my eye. Turning to the box, I lifted the opaque lid and there was the eclosing butterfly. I started a video and then moved it to a larger container with an upright dried twig which it immediately climbed up on. 

You can see the video of its emergence here. Watch closely and you can see it repeatedly extend and curl up its proboscis.  When they emerge, the proboscises of butterflies and moths consist of two C-shaped fibers called galeae, which are united after the insect emerges from the pupa, sealing the halves into a flexible tube.  Here you can see the two halves of the proboscis haven't sealed together yet and the left wing is curved and withered although it is flattening out over time. Eventually it was able to fly around in its aquarium.  The bluish color on the dorsal hindwing confirmed it was a female.

Proboscis in two halves
Empty chrysalis

Proboscis sealed at last
The problem now was that the outside temperature was a high of 30 degrees, dropping to 10 degrees at night.  By putting it in our warm house we had interrupted its winter diapause. With a lifespan of several weeks at best, even if it warmed up she had no nectaring sources, no male available, and no food plants for her eggs. She had no outlet for her biological imperative.  In retrospect, her only extremely long shot at reproduction would have been keeping the chrysalis in the refrigerator until our spicebushes leaf out in 10 weeks.

Of course that is all from an anthropomorphic perspective as no one knows what a butterfly perceives.  With a beautiful and delicate creature, it is natural to empathize and impart our human values.  While it was a hopeless situation for this creature, the only realistic response is to to do what Sharon did and in its memory plant spicebush (Lindera benzoin) and sassafras (Sassafras albidum), its alternate host plant, as well as native plants for nectar.  This spring, carpe diem. Then, like Sharon, you'll be able to say "I grow spicebush so that makes me happy to know the little guys have found my plants"

More on proboscis closure is in this paper.
For much more detail on proboscis function try this source, and may the force be with you.