News & Articles
Browse all content by date.
A week went by when I didn’t have a chance to check on the monarch caterpillars near the Cable Natural History Museum’s front door. So after I’d waved goodbye to the last fly-tying, canoe-paddling, snack-eating boy, I deserted the pile of dirty camping dishes in the sink, and rushed out to check on my caterpillar crew.
The milkweed looked like it had seen better days. Many leaves were completely missing, while others were chewed down to a yellowing stub. While the evidence of their voracious eating was all around, a quick glance revealed no caterpillars. So I searched harder and harder; checking under each leaf, peering under the pendulous flowers, until I satisfied myself that the caterpillars were nowhere to be found.
A little research confirmed what I suspected. Once a monarch caterpillar has reached its final instar and stops eating, it enters a wandering stage and travels some distance from its host plant to find a safer, less visible place to pupate. Somewhere in the sweetfern thicket on our hill, hang four delicate, pale green chrysalids. (Side note: If you’re wondering about my spelling, both chrysalis and chrysalid are correct terms for the pupa, and chrysalid is easier to make plural.)
Since I had hoped to have a front row seat during the caterpillars’ transformation into adults, I was more than a little disappointed. The blinking orange light of my voice mail inbox soon changed that.
Bob Olson, one of my readers, just had to tell me about his granddaughter, Eve Depew. This bright-eyed six-year-old is raising over 50 monarch butterflies on her back deck in Hayward, WI. She (with the help of her supportive parents) plans to save the monarchs from extinction.
As I chatted with Eve and her mother, Brianne, near the wood and netting butterfly nursery that Eve’s dad built, we kept one eye on the action. A neat line of chrysalids dangled from the sunny side of the frame, interspersed with crumpled, empty shells and their orange-winged owners. (It was too cold to release the seven new butterflies today.)
Hanging in one corner, a brightly striped caterpillar stuck out like a sore thumb. He’s in the J” spouted Eve, “I hope he changes soon!” Looking closer, she noted how the white stripes were looking greenish, and amended her exclamation, “I think he’s almost ready!”
While this caterpillar still looked more like a larva than a butterfly, some important changes had already taken place. During the wandering stage (when Eve must rescue wayward caterpillars off the deck furniture), veins develop that will supply his wings with fluid. As the caterpillar pupates, each wing is shaped and ready for adulthood.
During a pause in the conversation, we looked over to see that the caterpillar’s J was relaxing. “He’s ready!” announced Eve, swinging her blonde braids over her shoulder.
Sure enough, the skin near the back of his head had begun to split, and a small triangle of green showed through. Almost imperceptibly, this triangle grew as his exoskeleton sloughed off and crumpled into a wad near the silk button that attached it to the wood. It is easy to think of a caterpillar spinning a chrysalid around itself, but the delicate green shell is actually the body the caterpillar reveals during its last molt.
I stuck my nose up to the screen for a front row seat, while mother and daughter giggled together, narrating the action and imitating the energetic wiggling and twisting that the caterpillar must do in order to kick off the last of its old clothes without falling. This is no easy feat, as the monarch must pull a small, stick-like cremaster out of its exoskeleton and poke it into the silk button to secure its attachment for the long hall. This is a risky time for the monarch, and Eve told me sadly of one pupa that failed this step, its life ending in a pile of mush on the ground.
The newly-formed pupa looked lopsided to me, and upside down. Eve assured me that this was normal. In a few hours, the chrysalid’s exoskeleton would shape up and harden off.
Throughout my stay, both mother and daughter impressed me with their detailed knowledge of the life cycle. Only when I asked about the mysterious changes that happen inside the chrysalid did Eve furrow her brow and say “I just don’t know.” Scientists are only just beginning figure out the details themselves.
While the pupa is certainly soft and vulnerable as it forms, it isn’t quite the soup of cells that some people imagine. At no time do all the body parts break down, although the chewing, crawling muscles of the caterpillars are reduced to liquid and reformed into the flight muscles of a butterfly. During the final caterpillar instar, clusters of cells called imaginal disks started to grow rapidly. Besides the wings, they have already formed a beating heart, a respiratory system, antennae, legs, and a proboscis. Those parts and others just need more time to develop fully, and old caterpillar parts need to be digested and reabsorbed.
As I sat transfixed by the show, Eve told me how she gathers fresh milkweed (complete hitchhiking eggs and caterpillars) from a neighbor’s field every day, and cleans the copious caterpillar poop out of the enclosure. “She spends hours out here,” her mother said with a proud smile. “I think she’s going to grow up to be a scientist.” In my opinion, this little caterpillar is already well on her way.
For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Lake Alive!” opened May 1, 2015, and will remain open until March 2016.
Find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot, http://cablemuseumnaturalconnections.blogspot.com.