Friday, July 24, 2015

Monarch Chrysalids

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 seven-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 to 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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

As the developing monarch butterfly gets close to completion, the exoskeleton of the chrysalid becomes transparent and brightly colored wings show through. Photo by Emily Stone. 

Six-year-old Eve Depew is raising more than 50 monarch butterflies in an effort to protect them from weather, predators, and all the dangers of the wild. She hopes her efforts will help their populations recover. Photo by Emily Stone.

Friday, July 17, 2015

Boys on the River: Imitators and Attractors

The first ten miles of our trip went quickly. Once their paddles hit the water, the six teenage boys on our Paddle the Namekagon canoe trip didn’t want to stop. Looping around wide, lazy corners. Bouncing through short sections of mild rapids. Getting the hang of steering…and learning how to duck, or how to extricate the boat from tree branches when the steering didn’t work. My co-leader (a National Park Service Intern) and I gave them paddling tips, encouragement, and a lunch break, but mostly we just hung back and let them be boys on a river.

Arrival at the campsite meant learning how to set up new tents, laying out sleeping bags, and then an eagerly anticipated swim.

With the boys cooled off and tired out (for a few minutes anyway), our guest instructor came in. John Kudlas is a long-time outdoorsman and Museum volunteer. As a retired high school biology teacher, he is a wealth of knowledge and skills. Soon the boys were off on a scavenger hunt, looking for aquatic plants, identifying forest trees, and even collecting macroinvertebrates – the insects that spend at least part of their lives in the river.

With practiced efficiency, and his usual humor, John made sure the boys knew how important those invertebrates are. Both the aquatic nymph stages and the flighted adults of things like stoneflies and mayflies are water quality indicators, as well as good fish food. At the mention of fish, I saw the boys perk up their ears. As a surprise treat, John whipped out fish hooks, homemade hook vises, spools of thread, feathers, and fur, and soon the aspiring anglers were creating artificial flies for fly fishing.

This was delicate work, and the boys’ concentration was palpable. I noticed the tip of at least one tongue bitten in concentration. The long, brown nymphs each pair soon created were “imitators,” or artificial flies that seek to deceive fish by being a lifelike imitation of their insect prey. The boys were in good company. Humans have been creating imitators since at least 200 AD, and the term “artificial fly” was made popular by Izaak Walton’s 1653 book, “The Compleat Angler.”

By the mid to late 1800s, fly fishermen had expanded from tying flies that just imitate prey, to tying “attractors” – more colorful, abstract flies that don’t look like prey, but somehow incite aggression and attract strikes from fish.

Our boys followed the same progression in their fly tying.

After an easy morning paddle, we met Ranger Jeff at a large landing site. Since the Namekagon River is National Wild and Scenic Riverway—a unit of the National Park Service—we get incredible support from a host of park rangers along our journey, as well as some funding from the St. Croix River Association.

As it turns out, Ranger Jeff provided the real “bling.” A picnic table at the grassy landing was all set up and waiting for us. Here were professional hook vises for each student, as well as brightly colored foam sheets, vivid pink and naturally colored feathers, sparkly tinsel, and scope for the imagination. Ranger Jeff has a passion for teaching the next generation about fishing, and it showed in his enthusiasm, preparation, and carefully thought-out teaching progression.

As Ranger Jeff walked the kids through the fly tying steps, I could see both their eagerness to do things right for Jeff, and their confusion over how this odd hodge-podge of materials would become an artificial fly. Cutting foam, wrapping thread, folding, wrapping again, adding feathers, and wrapping some more—both the method and a form gradually took shape. Soon we had a swarm of brightly colored, flashy artificial flies with polka dots, eyes, tails, tufts, and even a comical unibrow.

Ranger Jeff gave the boys some free time then, to stretch their legs and get out their wiggles. He also put out a book of fly-tying patterns, opened up a case of professionally tied flies, and gave the boys the option of tying a second fly. After about ten minutes of Frisbee, they were all back at the table, heads bent to the task.

With the basic techniques mastered, the boys had soon created a second swarm of brightly colored flies, this time with multi-colored mantles, artfully layered feathers, and gracefully flowing tails. Thought definitely not imitators of life, these works of art looked like they could attract a crowd, and hopefully a fish, too.

Then for the real test. Ranger Jeff rigged each of the boys up with a fly rod and an artificial fly—hook and all. We waded into the shallow water at the river’s edge, and began to cast. Back and forth, the lines arched gracefully (mostly) over their heads and out into the current. Flies landed briefly on the surface, dancing in the ripples. Once again, the boys’ concentration was palpable. Cool water rushed around their knees. Flowing sand nestled around their feet. The jokes paused. Time slowed.

Imitators. Ranger Jeff stood in the middle of the row of young anglers casting again and again. I noticed the boys glance sideways at him from time to time, then turn back to their own rods with a focus on emulating his graceful motions.

Attractors. The river is its own lure: its peace, its beauty, its constant motion; the promise of challenge, adventure, and fun. And perhaps, if you tie the perfect fly, and cast the right way, the strike of a fish on your line.

In the preface of “The Compleat Angler, Izaak Walton wrote, “No man is born an Artist nor an Angler.” That may be true, but I think that on this trip we inspired a few of each.

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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, July 10, 2015


Lunch bag in hand, I hurried up the Cable Natural History Museum’s front walk, ready for another day at the office. On a whim, I detoured over to one of our native plant gardens. The round, pink cluster of flowers on a common milkweed drew me in, and I leaned over to inhale a big dose of their heady aroma.

As I finished drinking in their sweetness, my eyes opened, and then popped open wider. Caterpillar! There was no mistaking this wrinkly, black, yellow, and white-striped critter. Monarch butterfly caterpillars are as distinctive and easy to identify as their orange and black adults. Only an inch or so long, this little one was lying quietly on the upper surface of the leaf.

For a second, I worried about the folly of its bold, sunny perch. Shouldn’t it be hiding away in the shadows, safe from the hungry eyes of birds? It only took me a second to remember that monarch caterpillars don’t need to worry about that. As they munch on milkweed leaves, monarch caterpillars accumulate toxins from the plant’s milky sap in their bodies.

Not only do these chemicals make the caterpillars taste awful, they also cause any bird who eats the caterpillar to puke it back up. The bird remembers the experience, associates it with the caterpillar’s bright warning colors, and tends not to repeat the experiment. One caterpillar may sacrifice its life for the survival of its siblings.

So, with this protection in place, monarch caterpillars can focus on their most important task: eating. Monarch eggs are tiny – the size of a pencil tip – and develop for only four days before they hatch. The resulting caterpillar has a lot of growing to do. Over the course of just two weeks it will eat almost constantly. All that chewing takes a strong jaw – the average caterpillar's head contains 248 individual muscles. The goal: increase its body mass to more than 200 times what it was at birth. To accomplish this, a caterpillar eats its own bodyweight in food – milkweed leaves – each day. Some caterpillar species gain 20% of their bodyweight in a single hour. If I were to do that, the lunch bag still clutched in my hand would need to weigh over 28 pounds!

As they balloon in size, monarch caterpillars shed their skin five times throughout their larval life, each time revealing a larger skin waiting just beneath. Each stage is called an “instar.” The final time a caterpillar sheds its skin, it exposes the beautiful, jade-green chrysalis, and the monarch pupates.

Intrigued now, I squatted among the plants to look for more caterpillars, or eggs, or chrysalises. In my experience, two- and three-year old humans are the best height for executing caterpillar treasure hunts. Although no toddlers were available to help at the time, just taking their perspective won me two more tiger-striped larvae hanging out under leaves.

The basking caterpillar on the leaf’s upper surface still bothered me, though. Why not be better safe than sorry? With a little research, I soon turned up a scientific study in the Journal of the Kansas Entomological Society from 1981 that addressed that question. Rawlins and Lederhouse also noticed the basking behavior of monarch caterpillars. They, too, asked “why?”

What the researchers found, is that more often than not, the caterpillars rested in the sunshine in the middle of the day. Not only did they stay on the upper surface of the leaf, they also oriented their body broadside to the sun, for absorbing maximum solar radiation. The resulting increase in body temperature (up to 14 degrees Fahrenheit above the ambient air temperature) actually helped them to eat, digest, and grow faster.

In addition, the researchers hypothesized that increasing their visibility to birds actually helped caterpillars teach more potential predators about their toxic taste.

Female butterflies facilitate their caterpillars’ basking behavior by preferentially laying eggs on milkweed plants in the full sun, instead of in shady, wooded areas.

At night, caterpillars reverse their technique. On all but the warmest nights, caterpillars hide out underneath the leaves, shielding their body heat from the cold pull of the stars.

As the sun began to set outside my office window, I decided to go check on my little buddy to see if his behavior had changed. The dusk was cool and sweet. There he was, perched just where I left him. Only now, a crumpled gray wad of old skin lay next to him on the leaf. Was I imagining it, or did he seem a little bigger? While he rested, a neighboring caterpillar gnawed furiously at the jagged edge of another leaf. Grow, caterpillar, grow!

Friday, July 3, 2015

Home Again: Clay-colored Sparrow

A light rain was just starting to taper off as we crashed through the brush. The spicy fragrance of crushed sweet fern tickled our noses pleasantly. Birds sang all around us. Pushing through the clumps of head-high, stump-spouting scrub oak and red maple, we stepped carefully over the sooty remains of trees. Coming up on a long, narrow open area, a tall metal pole appeared out of nowhere – like finding the lamp-post in Narnia.

With a little squinting, we soon noticed some filmy, black netting strung from the pole, 30 feet through the open area, and hitched to a matching pole. A few raindrops sparkled on the web. Here, our small group of Wisconsin Master Naturalist students gathered around Jim Bryce, a retired biologist with the USDA Forest Service and National Park Service, and long-time bird bander.

Briefly, Jim explained how the mist net works. The fine black threads are nearly invisible, and they are strung to form long, floppy pockets. When an unsuspecting bird flies into the net, it drops into a pocket, and gets tangled in the net. Then a bander can carefully extricate the bird for processing.

As he talked, we noticed a flutter at the far end of the net. “Looks like we got one,” observed Jim, as he pushed toward it through the brush. And then, with considerably more excitement in his voice, “It already has a band! This must be the same clay-colored sparrow we caught last year!”

Returns – re-catching a previously banded bird at least three months later – are rare in the banding world, but they provide a wealth of information. From these recaptured birds, scientists have learned about the incredible 24,000 mile round-trip migration that Arctic terns complete each year; the wintering habitat of Bicknell’s thrushes; and the maximum known age for a wild bald eagle (32 years, 10 months). However, only about 1% of small birds are ever caught again.

“This is the perfect habitat for clay-colored sparrows,” Jim explained as he gently untangled the banded sparrow’s feet, feathers, and beak from the net. The Forest Service has been managing this area as open brushland, using fire to keep out the trees and provide the dense, shrubby, cover that many species need. That’s why we were stepping over burned logs and pushing through thickets of fire-dependent plants on the way here.

Clay-colored sparrows need this brushy habitat. Females build their nests in the lower branches of impenetrable thickets, preferring a spot with as little light penetration as possible for protection from predators. A low nest is good for the fledging chicks, too, since they hop to the ground before they can fly, and hide in dense thickets nearby while their parents feed them for a few more days. Unlike most other species, adult clay-colored sparrows forage outside of their nesting territory throughout the whole process. This leaves more food available near the nest for the flightless chicks.

Mostly due to a loss of their preferred brushy habitat, clay-colored sparrows have been in a slow decline over the past 40 years. That is one reason why the Forest Service’s management plan here in the Moquah Barrens on the Bayfield Peninsula is so important. Our returning sparrow is proof that they are doing a good job. Jim’s annual bird banding here will help to quantify their success.

When we finally got the sparrow extricated from the net and back to the processing table, we confirmed that he was in fact the same bird -- band # 53262 -- we caught last year in that same place. Male clay-colored sparrows return to the same territory year after year, but pairs do not mate for life. Instead, each year during migration the females find a new mate and follow him home.

The government will be following him now, too. At the end of each year, Jim reports all of his banding data to the USGS Bird Banding Laboratory. They’ll make note of this return. The Forest Service will be interested in that information, too, since it helps to validate their management plan. If we or someone else catches our little friend for a third time, they can report it to the laboratory, too, and we’ll gain even more information.

Jim spent a few minutes with our bird, measuring his wing length, tail length, and weight. Once the data was collected, a student placed our little brown-and-white streaked friend gently on the ground. We held our collective breath for a second as he got his bearings, and then with a flutter he was gone.

As we turned back to the table to process more birds, we heard the characteristic bzz-bzz-bzz song of a clay-colored sparrow, claiming this beautiful brushland as home.

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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, June 26, 2015


A pungent, earthy, vibrant aroma seemed to squirt out of the bog with every sinking footstep. Even through the soles of my muck boots I could enjoy the varying textures of this living carpet. Soggy sphagnum moss offered almost no resistance, while the skeletons of tough twigs buried within the moss crackled, bent, and snapped. At some point in each footfall, the cushion of living and dead plants pushed back toward me just enough so that I didn’t fall through.

Bogs are a unique, almost alien landscape, with a charm all their own. Funny plants, few trees, and a wonderful, squelchy, squashy, shaky, shivery, sucking substrate can turn adults back into giggly, wiggly kids. These twenty-two Wisconsin Master Naturalist Volunteer trainees were no different as they spread out to explore the Secret Bog.

Squatting down next to a domed hummock, I peered into a miniature jungle. Delicate vines of bog cranberry – with bright pink, swept-back petals on their tiny flowers; the wiry lattice of leatherleaf twigs; and bog laurel’s leaning stems with deep green leaves all poked their heads out of the mat of sphagnum moss like drowning rats. Sphagnum moss may be the bog’s bully – pulling itself up on the stems of others, using woody plants like scaffolding – but it is also the reason that the bog is here.

Sphagnum’s primitive leaves are like tiny sponges, and can absorb up to 26 times their own weight in water. This can raise the water table. Such a saturated environment is low in the oxygen that microbes need to accomplish decomposition, so nutrients stay locked up in dead vegetation. To deal with the lack of available minerals, sphagnum shoots hydrogen ions into its environment, dislodging scarce nutrients for its own use. This acidifies the bog, which further limits what plants can grow there.

Life is not easily discouraged, though, and a special suite of plants thrives in sphagnum’s world.

Peering over the side of the hummock, a sparkle caught my eye. Looking closer, I discovered a cluster of bright pink, hairy spoons, only an inch or two high. “Sundew!” I squealed, pulling over the nearest student naturalist to exclaim about it with me.

Round-leaf sundew are beautiful little plants, with a circumboreal distribution (around the Northern Hemisphere), and a penchant for animal flesh. Well, a taste for insects and spiders at least.

Sundews love the sunny, moist habitat created by sphagnum, but they still need to eat. Nitrogen is a limiting nutrient in bogs. Some plants get their nitrogen through complex root systems and relationships with fungi, while others conserve it with the austerity of evergreen leaves. Sundews catch bugs.

The sparkle that caught my eye was actually a drop of “dew” clinging to the tip of a tiny tentacle. The bowls of sundew’s spoon-shaped leaves are dotted with these tentacles. Long ones hold a drop of sweet, sticky nectar that attracts and entraps prey. Once an unsuspecting insect has been mired in this mucilage, the leaf curls inward. This response to touch is known by the comical term: thigmonasty. From the bug’s perspective: thing most nasty.

Death usually occurs within 15 minutes, as the prey succumbs to exhaustion or is suffocated by the goo. Shorter tentacles, with drops of digestive enzymes at their tips, make contact with the prey and reduce it to nutrient-rich soup, which is absorbed through the leaf surfaces. The valuable nitrogen is use to make chlorophyll, enzymes, proteins, and seeds.

The seeds are produced in a delicate, white-petaled flower held aloft on a long stalk. But how, might you ask, does the insectivorous sundew avoid eating its own would-be pollinators? In nature’s wisdom, a completely different set of bugs is attracted to the flower from those who are lured in by the saccharine dew.

The group of students was lured in, too, a few at a time, to look at the impressive patch of sparkling leaves. As we headed back to solid ground for our closing discussion, I plucked a little cluster of sundew leaves to bring in for a closer look. At first I was annoyed when the tentacles stuck stubbornly to my finger. Then I chuckled at my own surprise. It seems that Master Naturalists are no more immune than bugs to the cloying charms of sundew.

Friday, June 19, 2015

Chicken of the Woods

“Did you see that giant chicken!?” exclaimed my co-worker Jayme as she stepped out of her Jeep in my driveway. My puzzled look must have answered her question. “There’s a huge chicken of the woods right next to your driveway! It’s bright orange. I can’t believe you missed it!”

Jayme’s excitement was warranted. Chicken of the woods (a.k.a sulphur shelf) are choice edible mushrooms, and she is an enthusiastic mychophagist (mushroom-eater) and wild forager. A little embarrassed that I had missed such a neat find, I joined her and Steve, her partner, on a quick hike back up our long gravel drive. “I won’t tell you where it is,” she teased, “let’s see if you can find it yourself.”

Once I was looking, it wasn’t hard, but I did discover why I hadn’t seen it before. Tucked away up a steep bank, several yards back in a balsam thicket, the cluster glowed orange on the cut stump of a fallen tree. We grabbed baby birch stems and kicked our toes into the dirt, clambering up the near-vertical road cut.

It was impressive. Nearly two feet across, with layer upon layer of rippling brackets giving it a ruffled appearance, the yellow edges and undersides contrasting with rich, orange caps – this mushroom was beautiful.  It is also unmistakable. David Arora, author of “Mushrooms Demystified”, includes chicken of the woods in his “foolproof four.” Upon closer inspection, we found that the cluster was fresh, clean, and flexible. Just ripe for eating.

We reached into the mass, and gently tugged free a few of the most fresh and tender looking caps. The flesh was cool and moist to the touch, with a texture like fine velvet. Part of this consistency comes from it being a polypore. Unlike stereotypical mushrooms with the umbrella-like cap and radiating gills, polypore mushrooms are composed of many small, vertical tubes. Reproductive spores are produced on the sides of the tubes, and use gravity to disperse out of the bottom opening. From there, the spores use wind and animals to disperse them into a new home, eventually growing more mushrooms.

The pore structure also contributes to the succulent, stringy texture of the caps, which reminds some people of chicken meat. Soon we had tugged free enough caps to share with everyone for dinner.

Cooking mushrooms is extremely important for both safety and nutrition. Heat can denature toxins, kill nematodes, and break down tough cell walls to give our bodies access to nutrients. After wiping off a few specks of “trail spice,” we added the orange caps to a warm skillet in a pool of melted butter and garlic. With a lid to help keep in the juices, the “chickens” were soon sizzling merrily.

The first bite was the best: chewy but tender, with a light lemony undertone and a touch of the savory umami flavor, too. Though we wanted to keep eating, each of us tasted only a couple of small pieces. Chicken of the woods causes mild stomach upset in some, and allergic reactions in a very few. With any wild mushroom, it is best to try only a little at first, to gauge how your body will react.

After a comfortable night, I headed back to the stump to collect more. The wood still looked solid, so I suspect that this fungus will be back again next year. Chicken of the woods is a parasite (it kills trees) and saprobe (it decomposes dead trees), most commonly on oaks. After years of decay, it renders the wood – especially the heartwood – into a friable mess of brown cubes. Until then, it may fruit in the same place year after year.

And until then, I will continue making it part of my dinner. As I pulled off more chunks for my skillet, I noticed slugs and flies dotting the yellow undersides of the brackets. In just a few days, its brittle flesh would be riddled with insects, slug trails, and beetle holes. The fungus will die back. The decomposer will decompose.

The tree feeds the fungus. The fungus feeds the animals. Eventually the soil will feed a tree. And somewhere in that cycle, is me.

Chicken of the Woods, Photo by Emily Stone

Saturday, June 13, 2015

Old Turtle

The old turtle scraped at the sand with her naily toes as the kids gathered in a wide circle around her. Sometimes I get questions about dinosaurs on field trips, but they don’t fit into the Museum’s focus on Northern Wisconsin species. Today, instead, the first- and second-graders got a close-up look at a creature who has existed on Earth for over 40 million years, with direct ancestors much older than dinosaurs.

Quietly and respectfully, the students observed as the mother slowly finished excavating a depression for her precious cargo at the edge of the boat ramp’s asphalt. We commented on her smooth, algae-covered shell and enormous claws on her webbed feet. Once, I caught a glimpse between her hind leg and knobby tail of a smooth, white eggshell sliding into the nest.

The size and age of a female snapper, and the number of eggs she lays each year, are all connected. A mother turtle will only lay a clutch of eggs equal to about 7% of her body mass each year, and some years not at all. This helps make sure she’ll have enough energy to survive the winter, and translates into somewhere between 11 and  87 eggs, with an average of 34 eggs per clutch in northern populations.
Because of this trend, female snapping turtles don’t mature until they are eight inches long -- big enough support a clutch of about 22 eggs. With our short growing season in the north, that can take 19 years. This big mamma was well over a foot long. How many years must it have taken her to grow that big?

One reason that snappers grow so slowly is that they are ectotherms who use their environment to regulate body temperature. In the summer, they sun themselves to warm up. After a long winter, they have to wait until the shallows reach at least 40 degrees in order to become active.  Even then, they don’t start eating until the water temperature reaches about 60 degrees. This means that in cold northern lakes, snapping turtles may go nine months without eating.

Once they do warm up enough to eat, over half of their diet is vegetation. Snapping turtles are important scavengers, and may improve fisheries by eating the slow, bottom-feeding fish (which are generally unpopular among anglers). Although baby ducks do make the occasional tasty snack, they are a much less common part of the snapper diet than many people think. Over the course of a year, a snapper will only eat its own bodyweight in food. That isn’t a recipe for quick growth.

One consolation for their stingy diet may be that snapping turtles rarely become food for something else. The eggs and little guys are vulnerable, of course, but once their carapace reaches three inches long, they have no more natural predators.

Getting there is the tough part.

The eggs we just watched being laid have almost no chance of reaching maturity. For one, their location at the edge of a driving surface is pretty risky. But even in a good location, only about 14% of clutches hatch each year. Nest predation, temperature variation, and dehydration are all constant dangers.

Temperature is especially important. The embryos won’t develop at temperatures cooler than 68 degrees Fahrenheit. Above that, interesting things happen. Because turtles evolved before x and y chromosomes, they developed a system to use temperature to determine the sex of the babies. At 83 degrees Fahrenheit, the number of males and females will be equal. Cooler temperatures will produce males, and higher ones will develop females.

It is amazing that this lumbering matriarch even survived to this point in time. But turtles are survivors. Fossils of the most primitive turtle put the age of this group at 215 million years old – about 100 million years older than dinosaurs. Turtles survived the meteorite impact and the dinosaurs’ great extinction.

Reluctantly, the students left the great mother to her important task, and began one of their own. With nets and enthusiasm, they caught critters in the weedy shallows. Soon a shout rose above the rest, “I caught a turtle!” With its spiky shell, just over an inch long, this new stage in the life of a snapper – a baby hatched last year – captivated their attention just as thoroughly as the one before it.
This baby snapper, caught the same day, must have hatched last year. It gives hope for the future. Photo by Emily Stone