By Pat Foster-Turley, Ph.D.
March 17, 2022
My friend Susan Gallion was taking care of our cat Dumela when we recently went away on vacation. As usual, Susan sent me photos of Dumela at her cutest. But one day she texted me a photo. “What is this thing that Dumela is playing with? Whenever I try to take it away from her and put it on a shelf, when I come back the next day it is somewhere else in the house!”
The “thing” was a cylindrical object looking almost like a turd, but upon closer inspection it was lightweight and hollow. “No problem, Susan, it’s a moth cocoon.” One of these empty cocoons show up on our front doorstep every year about this time, and I’ve been saving them. The ones we find are hollow with an open end, where the moth has made its way out to fly as an adult. The empty cocoons are sort of like a ping pong ball—easy for a cat to toss and chase around. These cocoons are a favorite toy for Dumela as Susan discovered for herself.
We know that these are some sort of silk moth cocoon, and that Florida has a number of large attractive silk moths, but which one is it? Since the ones we have found are empty we have no idea. Our best guesses are either a luna moth or a Polyphemus moth, both striking in their adult form, and both forming cocoons made of silk. Butterflies do not make cocoons, they make chrysalises that have a hard shell, are often colorful, and contain no strands of silk. Only moths make cocoons.
Silk moths raised commercially are of a different species that make cocoons with finer strands that can be woven into silk cloth. These commercial silk moths cannot fly and must be farm raised. In Cambodia I visited a silk farm where thousands of these silk enshrouded cocoons are nurtured, the adults raised and the abandoned cocoons are dried and turned into silk cloth in a multi stage process. Cambodia has a variety of silk moths that are adapted to the hot, humid climate there and feed on a native variety of mulberry. Silk moths raised commercially in other places in the world spin fine white silk, not golden threads. Florida silk moth cocoons are made of coarse white strands and not generally used to make silk cloth, although I guess it is possible.
Well now we have a chance to see for ourselves what is inside one of these cocoons. During recent high winds a number of branches from our “self-pruning” river birch tree got blown into our yard. Usually picking up twigs and mowing the lawn is Bucko’s task, but now that I am into building my backyard fire, I eagerly recovered all these dry twigs and sticks and branches and piled them near my fire pit for future use. I thought Bucko would be pleased with my help, but his first comment upon seeing the cleared lawn was “Where is the cocoon?”
Ever more observant than me, Bucko had noticed a cocoon on a branch that he intended to pick up later. We both went out to my new pile of sticks, and sure enough there was a silk cocoon hanging from one of them. And this cocoon has no exit hole and something hard and loose inside. Just maybe the moth is alive therein and it will emerge and reveal its identity.
So now we have clipped the cocoon to a window shade hopefully far above Dumela’s reach and we are examining it every day for any signs of an emergence. In our area Polyphemus moths emerge sometime in March so the time is right. Or maybe it’s a luna moth, with a similar cocoon, but theirs is usually wrapped in leaves and this one was hanging bare from a stem. Only time will tell. Stay tuned.
Pat Foster-Turley, PhD is a zoologist on Amelia Island. She welcomes your nature questions and observations. firstname.lastname@example.org