April 3, 2015
Polyphemus
The large, feathery antennae of this polyphemus moth identify it as a male. These delicate and sensitive structures can detect a single molecule of female moth pheromone from miles away.
Let this be a lesson to you all: The next time someone brings you a cocoon and you promise to store it in a cold place so that metamorphosis will be delayed until the following summer—do it! Don’t be like me and keep it on your desk, pulling it out from time to time to show people you think might be interested. If you do, you’ll have to deal with the same level of regret and guilt I’m experiencing. And let me tell you, it’s no fun.
I suppose I should back up a bit, to a day last summer when Lorayne Hrejsa stopped by. Lorayne is one of our park district school program instructors, a Kane County Certified Naturalist, and a good friend too. On that day, July 15, 2015, she brought us a large canning jar filled with sticks, leaves and, most important, a brand-new cocoon.
Lorayne proceeded to tell us how her neighbors had been spraying insecticide in their yard, at a time when she was outside as well. She looked down and happened to notice—in her words—”a huge green caterpillar running away from the fog.”
She scooped the larva up, marveling at its beauty—and size. She estimated it to be at least as long as her index finger, and about as thick as her thumb. From her description, we were pretty certain that the caterpillar was a species of giant silk moth. The question was, which one?
In the time between when Lorayne picked up the caterpillar and when she went to let it go, it had spun a wondrous creation of leaves and silk—a cocoon that would later on serve as a transformation chamber, as the larva metamorphosed into an adult.
We peered into the jar and tried to make some educated guesses with regard to species. We had basically three “suspects;” cecropia, luna and polyphemus. These species are the “big three” silk moths in our area, that is, the ones most commonly encountered.
Based on Lorayne’s description of the caterpillar, and the design of its cocoon, we ruled out cecropia and put our chips down on either luna or polyphemus. We made up our minds to wait it out and see what emerged in May or June of 2015.
And that’s where the regret sets in.
I had been pretty clear in my promise to Lorayne. I had told her that, as the months progressed from summer to fall, I would step down the cocoon’s storage temperatures accordingly, to mimic the falling temperatures cocoons in the wild outdoors would be experiencing. I figured this process would be a piece of cake, because it’s exactly what we do each year to prepare our Blanding’s turtles for brumation over winter. I also thought, sincerely, that I would stick to it, and that we’d end up with a giant silk moth emerging right on schedule– in late spring or early summer.
What I hadn’t counted on, though, was the number of times I would feel compelled to show off the cocoon over the the ensuing months. I found
myself working words like pupa, diapause and metamorphosis into conversations with friends, neighbors and even total strangers, each time hauling the canning jar out to show off its contents. Afterward, instead of putting it away someplace chilly, like the basement or the Hickory Knolls entryway, I returned the container to its spot on my desk.
By December the cocoon had been joined in its jar by a few other miscellaneous arthropods-in-waiting: a butterfly chrysalis rescued from some wildflower seeds that were being processed; a spider egg sac; and a goldenrod gall fly gall. These objects increased the jar’s teaching value, while simultaneously decreasing the chances that the critters’ development needs would be met.
January,February and March flew by, and I rarely gave the jar a thought, other than the occasional, “Gee, I really should move that cocoon. One of these days…”
The one time I did have the jar in hand, ready to relocate, the temperature outside was -2F; in our vestibule it was 30F. Concerned that the thermal change would be too drastic, I put the cocoon back on my desk.
And now here it is April. I was sitting at my desk Wednesday—April Fool’s Day—when I thought I detected a bit of motion off to the side of my desk. I turned my head and realized, with a mixture of amazement and dismay, that Lorayne’s big green caterpillar—the one I’d promised to properly care for—had metamorphosed into an elegant male polyphemus moth.
The goo that comes along with an eclosing, or emerging, moth was in a puddle underneath the big guy. He hung upside down on the outside of the canning jar, his six hairy feet grasping the seed head of the goldenrod gall’s stem. His wings dangled below his body, growing larger as they filled with fluid.
I was happy for the moth and his successful transformation—he’s a beauty, for sure! But I also was sad that he’s a good month ahead of the time when he could reliably find a mate. And I was filled with guilt, because his predicament was all my fault.
So now, as I write this, Nicodemus Polyphemus (I know it’s corny, but it’s timely. And goofy names are a Hickory Knolls tradition) (some day soon I’ll have to write about Axl Otto the Axolotl) is perched on the screen in my office. I’m not sure what moth eyesight is like, but I’m sure he can sense the great outdoors on the other side of the glass.
Because giant silk moths do all their eating as caterpillars, Nic has no functional mouthparts. He’s only here to find a mate and keep the circle of life going. His huge, feathery antennae are extended, in a vain attempt to detect the pheromones of a female polyphemus.
His only hope lies with me, and my only hope lies with you. If you, by chance, found a cocoon last fall; meant to put it someplace cold but didn’t; and now find yourself staring at a gorgeous, but lonely, female Polyphemus, could you please let me know? Nic and I would both be grateful.
Pam Erickson Otto is the manager of nature programs and interpretive services at the Hickory Knolls Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346 or potto@stcparks.org.