Butterfly Breezes of Fall

A gentle breeze rippled the surface of Gabimichigami Lake. Paddling steadily in the bright sunshine of early afternoon, we were grateful that it wasn’t a steady wind. More than a mile of open water surrounded us with no islands or points to hide behind as we crossed from one portage to the next on our annual Boundary Waters canoe trip.

Hillsides of young aspen and birch glowed golden in the distance. At first, a flutter at the edge of my vision made me think that an autumn leaf had somehow managed to fall half a mile to the middle of the lake. A closer look revealed the dark purple wings of a mourning cloak butterfly. In late September?

I’ve often looked for mourning cloaks in early spring, knowing that these are one of a few butterflies who overwinter as adults and emerge as the snow is melting. They feed mostly on tree sap, fruit juices, and the honeydew excreted by aphids, so it’s not hard for them to find food even before most flowers bloom. They make the most of sunshine even on cold days by spreading their dark wings and body to absorb warmth.

A mourning cloak butterfly suns themselves on a paper birch tree. Photo by Emily Stone.

The adults mate and lay eggs even before the leaves of their larval host plants emerge. After the caterpillars hatch and feast on willow, aspen, birch, or a variety of other tree leaves for a couple of weeks, they form a pupa. After another couple of weeks, they emerge as adults in June or July. This seems perfectly timed to take advantage of peak flower availability, but abundant nectar doesn’t tempt them to feast. Instead, the new adults pause their development and go into a period of dormancy similar to hibernation, called estivation.

Then, in September and October they begin another active period, presumably to build energy stores before their winter round of hibernation. While mourning cloaks aren’t considered migratory, there’s some evidence that some individuals do migrate, perhaps to find a slightly warmer place to overwinter. Wherever they go, they’ll snuggle into hollow logs, wood piles, and loose bark. Hopefully, wherever they hibernate also gets blanketed by insulating snow and becomes part of the stable environment of the subnivean zone.

Throughout the trip, I saw at least half a dozen mourning cloaks out over the water, dancing in and out of the dappled sunlight at our campsite, and briefly landing to bask on sunny, warm rocks. Seeing them reminded me of an early spring hike up to St. Peter’s Dome, when I photographed a mourning cloak sunning themselves on a birch tree.

Mourning cloak butterflies become active in fall after a period of summer dormancy. This one photobombed a sunny afternoon on Saganaga Lake in northern Minnesota.

Photo by Emily Stone.

It’s not a bad schedule, really. Emerge into the gently warming days of spring. Take a siesta during the hottest days of July and August. Enjoy a fall feast before tucking in for the winter. They use this plan to survive across North America and even in Asia and Japan.

I even spotted one mourning cloak as recently as last week on the Superior Hiking Trail above Silver Bay, Minnesota. After watching their irregular flight until they disappeared in to the forest, a flutter at the edge of my vision caught my attention just in time to watch an autumn leaf come to rest on the ground.

Small quaking aspen leaves carpeted the trail in a mosaic of yellow and green. They were evidence of yet another way that a Lepidopteran (butterflies and moths) survives the winter. Green leaves don’t usually fall from the tree, but the trapezoids of chlorophyll captured between the first and second veins on one side of the leaves’ midribs told me all I needed to know. These were the larval home of a tiny moth.

A moth larva creates this green and gold pattern in quaking aspen leaves.

Photo by Emily Stone.

Back in July, a small, brown moth with white-fringed wings laid an egg on the leaf petiole. By September, a translucent larva hatched and bored into the leaf’s petiole, causing the stem to swell into a small gall. Munching her way up inside the leaf under the cover of darkness, the leaf-mining larva interrupted the mechanisms the tree normally uses to draw chlorophyll out of the leaf during the waning days of autumn.

Such a tiny caterpillar would dry out in the summer heat if she tried to pupate high in the tree canopy. Instead, she timed her life cycle to hitchhike on a falling leaf down to the damp forest floor. Now there, she is stealing a few more bites of the green energy she’d hoarded in the leaf. Presently she will pupate in relative safety and an agreeable microclimate. The soon-to-be-moth spends the winter in her cocoon, which is loosely woven to the surface of the now-brown leaf.

Colorful leaves and colorful wings flutter on fall breezes, all getting ready for winter.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Flying Kittens

“Just hold her like this,” Kurt told me. So I carefully nestled my first two fingers into the soft, warm feathers around the neck of this tiny northern saw-whet owl, cradled her soft, warm torso in the palm of my hand, and secured her brown and white wings with my thumb and other fingers. My heart stopped for a moment, but under those soft, warm feathers I could feel her smaller heart racing.

Kurt opened the sliding door onto the deck of his cabin. I paused to snap a photo of her huge, yellow-ringed eyes staring back at me in the dim light. Then we walked out into the night. As we waited for all our eyes to adjust, I focused on the feel of this incredible being in my hand. So soft, so warm.

Mike Avara, another scientist who is recruiting volunteers for some exciting new owl research in Bayfield County, affectionally described saw-whet owls as flying kittens. Indeed, the feel of her took me back to childhood when my cousin Meggan let me, a member of a family with no pets, hold one of the several very new offspring of her barn cat. Even as a child, the experience provoked an intense sense of responsibility along with the joy of connection to another little life.

Kurt gave the go-ahead, and I opened my hand. There were a few sharp pokes of tiny talons on my palm as she took to the air, and we watched as her fluttering flight became silhouetted against the moonlit sky, then disappeared into the black of the nearby forest.

Regrouping, Kurt and I put on our jackets and headlamps to check the other set of mist nets. About the size of a volleyball net but so delicate as to be almost invisible, mist nets have been used for decades to capture small birds. Each June, our Wisconsin Master Naturalist Volunteer Training Course experiences bird banding in the Moquah Barrens with Master Bander Jim Bryce. In daylight, his nets catch chestnut-sided warblers, brown thrashers, and clay-colored sparrows. Saw-whet owls are the smallest raptor east of the Mississippi—about the size of a robin and weighing just around 90 grams—and so the same nets work for them, too.

For many decades, northern saw-whet owls were caught only incidentally when nets were placed to catch other owls or nocturnal birds, and ornithologists thought that they were rare birds. Then someone decided to play a recording of the male’s song near the nets. Captures skyrocketed! We now know that saw-whets are fairly common across their range, although like most birds they have likely declined due to habitat loss over the past decades.

In the center of his three nets, which he deploys on dry nights from the last week of September through October, Kurt has a speaker set to play the owl’s loud toot-toot-toot call over and over. This sound is easily mistaken for the back-up-beep of heavy equipment, except that the owls are often calling at a time and place where no one would be working. The nets were empty on our second check, but earlier the speaker had blasted right at us as he worked to extract the little owl from the net.

This repeated call is the source of their name, since sharpening each tooth of a saw on a whetstone results in a repetitive sound. The owls make less well-known sounds, too. While exploring a series of recordings, I came across a vocalization nicknamed the “strangled cat whine.” I’ve heard this spooky sound numerous times in dark woods, and never known that it was just a flying kitten.

The owl in the net clacked her tiny beak in dismay at her predicament, but made no other sounds. Kurt is a Master Bander who has been banding birds since 2000, so with his experience it didn’t take long for the owl to be free of the net. Once inside his cabin, Kurt quickly prepared a leg band. Issued by the USGS Bird Banding Lab, the unique number stamped into the aluminum will allow this bird to be identified throughout her life and across the entire continent if she’s ever caught again. Unfortunately, federal funding for the banding lab’s important work is at risk of being cut.

Banding birds like this saw-whet owl has provided scientists with a wealth of information over the decades. Photo by Emily Stone.

Seven to eight percent of the 350 or so saw-whet owls Kurt has handled have already been banded, by him or someone else. These recaptures are an amazing source of information about the movements, ecology, and lifespan of the birds. Even if a bird isn’t recaptured, the measurements Kurt took of the owl’s weight, wing chord length, and age provide valuable data. This owl’s wing chord length of 136 mm, paired with a heavier weight, is what told us she was female. Male raptors tend to be smaller.

We also shone a UV light on the underside of her wing, where fresh feathers glowed hot pink. As feathers age, the UV-reactive pigment degrades, and older feathers look faded. This little owl was hatched just last spring and had only recently molted all her juvenile plumage into adult feathers, so they all glowed brightly.

Band-new feathers on this underside of the wings of this young saw-whet owl reflect lots of ultraviolet light. Photo by Emily Stone.

By this time next year she’ll have some bright and some faded feathers. Maybe Kurt will find her in his nets again. Maybe Mike Avara will discover that she’s raising chicks in one of his nest boxes. No matter what, her few minutes of discomfort at the banding station will help us understand more about her entire adorable species and what we can do to help them navigate a changing world.

Learn more about the volunteer opportunities with Mike and Kurt's saw-whet owl nest box and MOTUS tower research on the Museum's iVolunteer page: https://cablenhm.ivolunteer.com/saw-whet-owl-research

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Green Frogs Prepare for Winter

Golden birch leaves glittered across the portage trail as we pulled our canoe up at the landing. My paddling partner and I inhaled deeply of warm afternoon air that was sweetly scented with fall. Hoisting the canoe onto my shoulders, I started off down the trail. It went downhill from there, and not the good kind of downhill.

 

Off the end of a rotten boardwalk we found more mud...

One stretch the portage trail was an old railroad bed and actually quite nice to walk on!

First was the huge patch of sticky mud that sucked at my muck boots and threatened to throw me off balance. A puddle of unknown depth hid slippery rocks beneath the murky water. The next wet patch was spanned by a boardwalk, but the single plank was narrow, slimy, and bounced like a teetertotter where supports had become unstable. Finally, within sight of the next lake, movement near the toe of my boot startled me almost to the point of disaster.

 

Beaver-flooded portage landing.

Big black eyes with golden rims stared up at me from the slope of a rock. Crooked toes gripped the rough surface, and long hind legs braced for a quick escape. The green frog who had jumped out from underneath my boot perched motionless, as if that made them invisible.

 

Looking closer, I was captivated by the coppery shine of their skin, with indistinct dark spots. Despite their name, just a swath around their smile was green, like a smear of Halloween lipstick. Many frogs shift their skin to a darker color on cool days to absorb more warmth from the Sun, which is one reason green frogs (Lithobates clamitans) in the north are often brown.

From their large size, I guessed that this frog was female. Looking back on photos, I could confirm this by the comparing the size of her tympanum—the external ear structure—to the size of her eye. They were roughly equal in diameter. This membrane transmits sound waves to the inner ear. Male green frogs’ tympanums are larger than their eyes, although scientists aren’t sure what benefit that provides.

 

Female green frogs have a circular ear patch called a tympanum that it about the same diameter as their eye. On males, the tympanum is bigger. Photo By Emily Stone.

Throughout the trip—six muddy portages, five lakes, and then back again—we spotted gobs of green frogs at the landings leading into shallow, weedy water, and no frogs at the graveled landings with clear water. Green frogs feed by sitting and waiting for anything large enough to see and small enough swallow. Mud and plants make great habitat for these creepy crawlies, and therefore great habitat for frogs, who also lay their eggs among emergent vegetation.

While we reveled in the pleasantly warm weather, the golden birch leaves on the ground and orange-tinged cedar boughs along the shoreline were a constant reminder that winter is on the way. At home, I’ve been hearing lonely spring peepers call loudly before dawn every morning, from just outside my open windows. Like wood frogs, spring peepers spend the winter just beneath the forest’s leaf litter frozen solid. They are one of the first to wake up and thaw out come spring.

Green frogs can’t tolerate being frozen, and so must find a place to overwinter where they are guaranteed to stay liquid. Often this is simply at the bottom of a wetland or pond. They slow their metabolism and absorb a little oxygen through their skin. Sometimes they take a cue from their cousins and nestle into lake-bottom leaf litter, which gives off a little bit of warmth as it decomposes.

While spring peepers must wake up in a hurry, call like crazy, then rush to lay eggs in woodland pools that eventually dry up, green frogs can take breeding season at a more leisurely pace. Lakes sometimes take a while to thaw. Then the large mass of water takes even longer to warm up. Throughout it all, green frogs don’t have to worry about their eggs or tadpoles drying out before hopping away, even though they don’t start making their banjo-like plunk calls to attract mates until the peepers are almost done.

In fact, green frogs sometimes overwinter as tadpoles, and might not metamorphose until their second summer. By altering the composition of their muscle membranes, the tadpoles maintain their ability to put on a burst of evasive speed even in cold water. This helps them escape predators without wasting energy by moving quickly all the time. Dragonfly nymphs, diving beetle larvae, and water scorpions are all predators who also survive winter under the ice.

My canoe paddle bumped the bottom on one super shallow lake, and I started to worry. What would happen to the frogs and all those beings if this tiny water body froze to the bottom? I later read that green frogs have been observed gathering around springs where groundwater bubbling up will stay at a steady, unfrozen, temperature throughout the winter. They must be good at finding other warm microhabitats, too.

One last green frog watched from a wet rock as we paddled up to the final portage landing. Even more golden birch leaves had fallen overnight, and a lonely migrating loon wailed a farewell from across the water. Each of us was preparing for winter in our own way.

 

Getting out on as many paddling trips as possible before ice up is our way of preparing for winter!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

 

 

 

 

The Mystery of Mast Years

Last week I wrote about acorns clattering across my roof. As it turns out, nuts are raining down on many of your roofs, too! Commiserating over the loud, foot-rolling acorns makes me feel like part of an extended community. Are the oaks part of a similar community? And why are they suddenly attacking us with acorns!

Oaks are mast species, which means that all the trees in an area will produce a bumper crop of acorns at the same time, but only every two to five years. With hundreds of thousands of acorns available, the trees ensure that at least some of them will escape being eaten by chipmunks, squirrels, turkeys, blue jays, deer, and bears and survive until they can sprout and grow. This is known as predator satiation.

Red squirrels are seed predators on acorns.

In non-mast years, the acorn seed predators still survive, but at lower rates. When the oaks do mast, there aren’t enough critters to eat all of the acorns. The seed predators feed greedily and reproduce, but when there are few acorns the following years, their populations drop again. By being unpredictable with their mast years, oaks prevent seed predators from syncing up with the trees.

This same idea applies to parasites. Acorn weevils, knopper gall wasps, and acorn moths lay their eggs in developing acorns so that their larvae have an easy meal. A bacterial pathogen takes advantage of the holes they chew and causes “drippy acorn disease.” The result is the same as a chipmunk eating the seed, but the process takes longer. In addition, the parasites and pathogens are often closely tied to the acorn as a food source, and may not have other options. Chipmunks and other seed predators will eat from an extensive buffet of foods when acorns aren’t available.

While teaming up to satiate seed predators is clearly a good strategy for oaks, scientists are not so clear on how the trees coordinate, sometimes across hundreds of miles. It can’t be totally weather or resource driven, since variations in rainfall and temperature don’t fluctuate as much as the number of acorns produced. Certainly, an oak can’t produce tons of acorns if they are not healthy. But a year with plenty of rain doesn’t automatically result in acorns. During mast years a tree’s growth slows, so sometimes the trees need to put abundant resources toward making wood, not seeds.

One hypothesis about how oaks coordinate their mast years that seems to be gaining support in the scientific community is pollination efficiency. Oaks are wind pollinated. Their male flowers are dangly catkins that release pollen into the wind. The pollen needs to reach the pistils of the much smaller female flowers in order to fertilize the nascent seed. When oaks produce a ton of flowers at the same time and then have warm, dry weather, more female flowers will receive their dose of pollen. If the number of flowers oak trees produce fluctuates from year to year, this could translate into variable seed production, too. According to one study, this is true in “soft” climates, but not the Northwoods.

In harsh climates like ours, oak trees produce about the same number of flowers every spring. Having warm, dry weather that allows flowers to be pollinated AND to develop into acorns is essential, says Dr. Andrew Hacket-Pain who has used data from the Nature’s Calendar Phenology Project to study the correlation. A rainy spring, late freeze, or ice storm can easily ruin everything. Knowing how patchy storms can be in the Northwoods, I’m hesitant to believe that this could coordinate mast years across huge distances.

“In the old time, our elders say, the trees talked to each other,” wrote Robin Wall Kimmerer in her book Braiding Sweetgrass. Do they gossip about the weather like most Northwoods neighbors? Some mycologists theorize that the networks of mycorrhizal fungi who connect a forest by the roots may be the agent of coordination for mast years. “A kind of Robin Hood,” wrote Kimmerer, “they take from the rich and give to the poor, so that all the trees arrive at the same carbon surplus at the same time. Through unity, survival. All flourishing is mutual.”

Mice certainly flourish alongside acorns in mast years. The abundant food source means they have more babies. The same is true for the mice’s predators. Foxes, weasels, ticks, and even saw-whet owls may increase in number when mice are abundant. I’m excited for the potential uptick in owls, because the Museum has just started to recruit volunteers to help with a saw-whet owl study in Bayfield County. Check our calendar of events for details!

From mice to owls to chatting neighbors, oaks, and the mystery of their mast years, are at the center of our Northwoods community.

Author’s Note: Portions of this article are reprinted from 2015 – which was another mast year!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

A Summer of Loon Discovery

The pontoon bobbed in the water as I stepped onto the deck, clutching binoculars and trying to contain my excitement. Since moving to the Northwoods in the middle of winter, I had been waiting for the chance to see a loon, and my chance finally arrived in late May. The sunlight danced across the water as our boat left the dock, and we began our search. It wasn't long before we spotted the silhouette of a loon off in the distance, and headed for a closer look.

This loon was one of the most regal beings I had ever seen. They swam through the water with quick ease, head held high, only occasionally paying us a bit of attention. It was as if they knew they had our full attention, and as a result flaunted with a casual indifference as they floated around the boat. Their black-and-white spotted back glimmered right along with the sun reflecting off the water, highlighting their natural camouflage. We watched them preen their pristine feathers for a while, before they dove below the surface and left us behind.

An impressive loon swimming near our boat. Photo by Heaven Walker.

My next opportunity to see loons was on Lake Namakagon in mid June. As our pontoon slowly cruised through a marshy area of the lake, we kept our eyes scanning the scenery looking for loons. It wasn’t long before we spotted a loon, tucked into the dense reeds and aquatic vegetation, doing their best not to be spotted by us. They were in their nest with their neck and head extended low in front of them, body going as flat as it would go. It seemed to me like they were trying to be absorbed into the reeds to avoid our attention. As a highly aquatic bird, loons only go onto land to nest. By doing this, they are at a higher risk from predators, because they are very poorly adapted to moving on land. To help remedy this, loons nest very close to the waters edge for easy access to the nest, and for easy access to the water. This particular loon's body language on the nest told us that they were stressed by our presence, so we slowly continued on by–doing our best not to disturb them.

This loon's body language indicated they were stressed about our presence. 
Photo by Heaven Walker. 

That day on Lake Namakagon was the first time I saw loon chicks. The cute brown fluffballs with webbed feet were floating around with their parents, learning how to be a loon. I watched as one of the parents dove, and resurfaced with a small fish. Then it was a race from the chicks to see who could reach the parent first, and gobble up their meal. The parents continued to dive and bring fish to the chicks, and the chicks went so far as to attempt to dive themselves. But they never managed to be under for more than a few seconds before their fluffy feathers had them bobbing back to the surface. Diving wasn’t the only behavior the chicks were learning. As I continued to observe the chicks, one of them flapped their tiny wings and stretched vertically into the air. A wing flap! This is a preening behavior done by loons to maintain their feathers, and keep them aligned properly. It was quite adorable, and comical to see the chick wave their wing nubs about.

A baby loon practicing their wing flap. Photo by Heaven Walker

But it wasn’t until finding surprise loon chicks on Lake Owen in mid July that I truly became invested in loons. This pair of chicks were born later than typical, even by second nesting attempt standards. When I spotted them on a Loon Pontoon Tour, they gave me a glimmer of hope for having successful chicks on Lake Owen–as there had been no other chicks on the lake that summer. I instantly became invested in how they were doing. Week after week, I searched for them on the lake. Whenever it would take longer to locate the chicks on the lake, I would get worried that they had fallen victim to a predator. But then I would spot them swimming in the distance, and my worries would be quelled until the next week. As of late August, they were roughly five-to-six weeks old, quite sizable and seem to be doing well.

My summer observing loons was spent taking in all the new information I could on these fascinating birds. I witnessed adult loons call out in warning of an eagle flying overhead, and watched them track its flight as it went by. I watched as they took care of young, preened themselves, dove for food, and swam over to investigate other loons. They have become a new fascination, and I can thank my time in the Northwoods for that.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Attack of the Acorns

Crack! Rumble, rumble, rumble. Crack! The sound of hard objects pelting my metal roof shot through my open bedroom window, rousing me from the last wisps of sleep. Then silence. I braced myself as a soft hush of wind drew closer. Crack! The wind triggered a new spatter of noises. The house was under attack—by acorns.

Two large red oak trees reach the edges of their canopies out over the roof of my house. Each fall, they create a racket as acorns drop on the metal roof, tumble down the steep slope, and launch out over the driveway. Some years are worse than others, since oaks are mast trees who will produce a bumper crop in one year, then spend subsequent years rebuilding their stores of nutrients and not producing as many acorns. This is clearly a mast year.

The acorn attack had preceded my alarm clock, but I decided to get up anyway. Taking my coffee with me into the crisp fall morning, acorns nestled in the grass rolled under my feet. I bent down for a closer look at the offending projectiles. The acorns with caps intact captured my attention first. They are the most adorable, after all. And the caps can be helpful in telling apart different kinds of oaks. Red oaks have a low-profile cap with artfully arranged concentric scales. Burr oaks, in contrast, have fringed brims on their acorn caps. Many of the acorns were cap-less though, a pale ring marking the newly exposed shell.

On the driveway, many acorns had been cracked open by my car tires. Some showed pure, cream-colored nutmeat. On others the insides were blackened and bedraggled. I’d read that trees will discard immature acorns that have been attacked by insects or fungi, and they fall to the ground with the cap intact. On the other hand, trees release healthy, mature acorns from their cap, which stays attached to the tree. Was this true?

Gathering up a handful of acorns with and without caps, I got out a cutting board and a Mason jar to use as a nutcracker. I chose a cap-less acorn first. Sure enough, a couple of bangs with the jar split the nut open to reveal intact tissue, ready to fuel the growth of a seedling next spring.

Next, I picked a capped acorn. It looked normal, but from the first tap I could tell it was mostly hollow. Sure enough, when the shell split, I discovered a fat white larva with a brown face had eaten more than half of the two fatty seed leaves called cotyledons that make up the nutmeat. Another capped acorn produced at least four smaller larvae, all eating around the edges. One nutmeat was just shriveled and brown, with some white webby stuff at the bottom—likely a victim of fungi. Wasps, sap beetles, and acorn moths also attack acorns and consume the nutritious tissue inside. In my sample size of 6, all the capped acorns were being attacked, and the bare-headed ones were intact.

A note from my post of this photo to BugGuide.net:

This looks more like a Lepidoptera larva to me, but I'd need to see it from different angles to be more confident. Some moth species are known to feed inside acorns as larvae.

… John van der Linden,

… John van der Linden,

I chuckled as I remembered learning this lesson a different way. For our MuseumMobile visits to kindergarten classrooms in the fall, we fill a little cup with acorns. Kids shake the cup, listen to the rattle, and try to guess what’s in there. One fall, our educator filled the cup with fresh acorns, and when we went to show the kids, the cup contained several white larvae, and the acorns each had a small, round hole where they’d chewed their way out.

Likely, they are the young of acorn weevils. These little insects using their long, saw-like snout, called a rostrum, make a tiny hole just under the edge of the cap and lay one or more eggs inside the young acorn. The larvae are fine with the tree’s habit of discarding infected acorns, since they need a ride to the ground. Once there, they tunnel out of the acorn, burrow into the soil, and eventually pupate into an adult weevil.

While some squirrels seem to avoid weevil-infected acorns, others have been observed feasting on the tender protein-filled morsels. Perhaps it’s a question of whether the squirrel is going to cache a nut and needs it to survive the winter, or wants a juicy snack right now. Squirrels might shake or weigh an acorn to determine what it contains, but a quick way for a human to separate viable acorns from predated ones is to do a float test—viable acorns sink and the rest can be skimmed off the top and discarded.

The float test using two of my sample acorns. 

A scratchy rustle on the roof made me look up from the pile of cracked acorns just in time to see a full oak twig launch off the roof. Two fluffy gray squirrels looked guiltily down from the branches. A cluster of empty acorn caps on the lower part of the twig marked the tree’s success—or maybe a squirrel’s full tummy? Out toward the tip, though, in the axis of each leaf, were what looked like miniature acorns forming from the remnants of female flowers.

The squirrel who had tossed this twig onto my roof did me a favor—female oak flowers only occur high in the canopy and are hard to see. The male flowers—dangly yellow catkins that release pollen—are much easier to observe in the springtime. Once pollinated, the female flowers bide their time, and don’t fully mature until their second summer.

Unfortunately, what this squirrel also showed me is that next fall might be noisy, too!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Shades of Rot and Life

Author’s Note: This essay is a chapter from Emily’s third book, Natural Connections 3: A Web Endlessly Woven, which will arrive in November 2025!

In the dim light, under the thick, hardwood canopy of the forest, death was everywhere.

Autumn leaves carpeted the ground in shades of brown and yellow with occasional splashes of blood red. Snags stood among the living trees, their decorticated (a fancy term for barkless) trunks smooth and dry. And long stripes of rusty brown crumbles marked where fallen logs were melting into the ground.

Of course, life was everywhere too.

Beside the wide, dirt trail, a ruffle of turkey tail fungus cascaded down the graceful curve of a tree trunk like an earth-toned ball gown: a damsel of decay. While the volume of fungal frills—each with a velvety top, concentric bands of color, and tiny pores in the white undersurface—was impressive, the bulk of the being was hidden inside. Intertwined among the wood cells, hidden from view, the fine, white threads of hyphae (the actual body of a fungus) were hard at work. The tree was dead, and yet, still full of life.

Turkey tails are a white-rot fungus, which means that they have the ability to decompose the major components of a tree. That’s not easy. Wood is tough because the cellulose and lignin molecules it’s made of are long chains of elements that are difficult to break apart. Lignin in particular gives wood its strength.

Turkey tail fungus is rotting both the cellulose and the lignin in this log. Photo by Emily Stone.
 

Do you remember learning about enzymes in your high school science class? I chewed on a saltine cracker until it became sweet. Enzymes in my mouth broke down the long chains of starches until they became glucose, a simple sugar. In a similar, but external process, fungi exude a series of enzymes into the wood, and those enzymes split the chemical bonds of cellulose and lignin, resulting in shorter chains of glucose. The sugar dissolves in water, and fungal hyphae absorb it directly through their cell walls. Carbon dioxide is released to the air.

Because turkey tail and other white-rot fungi break down cellulose and lignin simultaneously but leave some of the cellulose for last, the wood they work on becomes white and stringy. A large portion of the nutrients once trapped in the wood become available to cycle through the ecosystem again. Bacteria move in to use those nutrients, paper wasps turn the pliable fibers into nests, and moose eat wood softened by artist's conk fungi.

The next day, I headed back along that same trail with a group of Wisconsin Master Naturalists doing an activity called a “Professor Hike.” I picked a student with a sense of humor, stationed her by a stump, and made her a duct tape nametag that read: Professor Brown Cubical Butt Rot. “This isn’t a disease caused by too much time in an office chair,” I joked. The name is real and quite descriptive.

As the professor explained to her classmates, this tree stump was being decomposed by a brown-rot fungus. Unlike the turkey tail, some fungi can only decompose the cellulose in wood cells, and the lignin left behind is brown. The fungus typically affects the bottom of a tree trunk, which in forester and logger lingo is the “butt.” But the cubical part of the name is most interesting.

Brown-rot fungi send hydrogen peroxide rapidly diffusing through the wood of a tree. The chemical modifies lignin just enough to get at cellulose also in the cell walls and snips apart the long chains of cellulose into carbohydrates. Two days later, once the destructive peroxides have dissipated, enzymes finish the job of turning the carbohydrates into sugar. The fungus absorbs it.

The process works more quickly than the totally enzyme-dependent decomposition by white-rot fungi but leaves all the lignin on the table. The lignin-rich wood turns brown, shrinks, and cracks into roughly cubical pieces. Hence the name, brown cubical butt rot. The “professor” bragged about her name all day—inadvertently teaching about decomposition along the way.

We’re often tempted to turn everything into a competition. Are white-rot fungi superior because they can break down lignin? Or are brown-rot fungi better because they can work more quickly? In fact, the first to arrive often has the advantage. And when the two types of fungi compete directly on the same log, brown-rot fungi win the short game by being able to access the energy in cellulose quickly, while white-rot fungi play the long game as they slowly devour more of the energy stored in the wood.

In the end, the ecosystem wins. The rusty colored crumbles of brown-rot fungi contribute to healthy soils with more capacity to hold moisture and nutrients. White-rot fungi, and especially competition between several different types of fungi, results in a tree being more thoroughly recycled and the materials becoming available for new growth. Humans are also treated to delicious meals when the fungi fruit. My favorite—chicken of the woods—is a brown-rot fungus. Shiitake and oyster mushrooms, plus medical turkey tails, are all white-rotters. Lignin and cellulose; brown and white; death and life. In the end, they aren’t all that different.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.