Friday, April 29, 2016

Queens of Spring

The gentle sound of waves lapping at the shore tugged me toward the lake. Finally, the last sheets of ice in my little bay had melted away under the persistent caress of a warm breeze. Late afternoon sunshine prickled the back of my neck. A dead branch lay across the trail, nestled in the moldering leaf litter, victim of the winter winds. As I stooped to pick it up, a bit of color caught my eye. Zooming low above the moss was a big, fuzzy, bumble bee.

I didn’t react quick enough to stop my momentum, so the flying branch scared off the flying bee. I did get a brief glimpse of a bright orange stripe in the middle of the classic black and yellow body.

I’ve seen a bee like this before, as it was wallowing in the bounty of summer on a dazzling prairie blazing star flower. Somehow I came to identify it as Bombus ternarius, a tri-colored bumble bee. The landscape on this April day, although warm and sprouting, was a far cry from that flower-filled August field. Most bees don’t fly this late in the day, even in summer.

Bumble bees, I knew, are able to fly at colder temperatures than many other insects. Flight muscles don’t work when they’re too cold, but the limits of bumble bee flight are lower than most. In addition, they raise their body temperature above the ambient temperature using a few neat tricks.

First, bumble bees readily absorb what little sunshine peeks through the spring clouds. Then they generate their own heat by shivering muscles without flapping their wings. It can take 5 minutes of shivering to raise their muscle temperature to the required 86 degrees when the air temperature is 55. Finally, the thick fuzz that covers their bodies insulates and helps retain their hard-earned heat.

All these adaptations mean that bumble bees can be active earlier in the spring, earlier and later in the day, and in more adverse weather conditions than honey bees and other not-quite-so-hairy bees.

Still, this early in the season, I must have been in the presence of a queen. Each fall the old queen bumble bees and all the male bees die in the cold, while newly fertilized queens find a safe, underground place to overwinter.  When they emerge in the spring, the queens are on their own for at least 5 weeks, until the eggs they lay become their  hard-working colony.

While you may imagine that all bees nest in a hive or hollow tree like the European honey bees we use to pollinate our crops, our native bumble bees tend to house their colonies in abandoned mouse nests or other underground burrows. The burrows are sheltered from the weather and pre-insulated with grass, thistle-down, and mouse fur. Many other types of native bees are solitary and don’t form colonies at all.

It takes a lot of fuel to keep a big bumble bee buzzing, so the queens will often try to locate their nest near a food source. Near this lakeshore, the only flowers I’d seen were on willows, but elsewhere, patches of Dutchman’s breeches are said to be a draw. These oddly-shaped white flowers are consistently some of the first blooms I spot in the woods.

Not just any insect has the strength and tongue length to forage for nectar in these little pantaloon-shaped flowers, though. The queen bee grabs onto one of the white flowers, and the one next to it too, for stability. Then she’ll burrow her tongue first and then her head into the flower and angle toward one of the nectar spurs. Throughout this process, the flower’s anthers brush pollen onto her head, thorax, and forelegs. Smaller bees can’t quite pry open the petals to access the juice bar inside and they sometimes cheat by chewing a hole in the nectar spurs.

While the plant’s goal for the pollen for is for it to travel to the female parts of another flower, the queen bee uses some of it—and nectar, too—to fill a tiny honey pot inside her burrow. This food will sustain her while she broods her nest. When the pantry is stocked, she lays her eggs. After four days the eggs hatch and she feeds the larvae on more nectar and pollen while they grow. After two weeks as larvae and two more as pupae, the queen’s hard work pays off when her daughters emerge as adults—full grown and ready to work.

Queen bumble bees are especially important pollinators in early spring, but throughout the year, Wisconsin’s thirteen species of native bumble bees contribute mightily by pollinating native plants as well as crops like tomatoes, peppers, squash, cranberries, and blueberries. Their capacity to fly in cooler temperatures and ability to muscle into certain flowers make them invaluable.

But bumble bees face the same threats as honey bees: parasites, pathogens, pesticides, invasive species, climate change, and habitat loss, among others. There’s quite a buzz around bees these days, and when you learn about them, it’s not hard to understand why. They are truly the queens of spring.

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 1, 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.


Tricoloured bumble bees are a brightly colored and easily recognizable native bumble bee. This time of year, until at least May, if you see one you can be sure that she’s a queen. Later in the summer you’ll mostly like see her worker bee daughters gathering provisions for the nest (like this one on a prairie blazing star flower). Male bees gather nectar for themselves, but don’t help provision the nest. Photo by Emily Stone.

Friday, April 22, 2016

The Symphony of Spring

A big truck rumbled by as I squeezed the brake levers and guided my bike onto the shoulder. The wonderfully warm, sunny afternoon had lured me out on an adventure, and my first stop was this small, roadside wetland. With a southwest exposure, this marsh thaws a day or too sooner than the one by my house, and I head here each spring to listen for the first frogs.

As the truck’s noise faded, silence fell over the forest. Peaceful, yes, but not what I’d hoped for. Could the wood frogs still be waking up? It does take them a little while to recover from being frozen all winter. With the arrival of warm temperatures, wood frogs thaw from the inside out.

Recovery is relatively rapid—especially considering what they’ve been through—but not instant. The frog’s heart starts beating before they are fully thawed. Breathing resumes soon after, and circulation begins as soon as their blood melts. That doesn’t mean the frog is ready to hop off into the sunset, however. It takes more than five hours for their leg muscles to regain some function and up to 24 hours for the frogs to exhibit normal body postures and coordinated muscle functions.

A couple days later, their mating drive kicks in. That’s what I stood there hoping for, in the silent woods. Then, from the back corner of the wetland came a soft quack. And another. Then a second frog called softly from another shore, and a third chimed in tentatively from near the road. From there, the chorus crescendoed until a cacophony of quacks, chuckles, and clucks echoed through the woods.

For the next few weeks, this wood frog choir will continue their performance whenever the temperature rises near 50 degrees and above. It is mostly males who call, and the impassioned sound serves to attract females to their pond. The more females their calling can attract, the better chance each male has of finding a mate.

As frogs arrive at the pond and mill around, eager males will search for a mate. They can’t see or smell a difference between females and other males, though. Instead, a male frog hugs another frog from behind and around its waist. Fellow males, identified by their slim waist, give a loud croak and are released. A slender female, who has already released her eggs, also gets a pass. But when a male frog grips a plump female—chock full of eggs—he hooks his thumbs around in front of her and doesn’t let go. This is called “amplexus.”

From there, the female deposits her eggs in a floating mass and he fertilizes them as they emerge from her body. Many wood frogs in a pool may lay their eggs together. The earliest breeders benefit from their eggs being in the center of the mass where they absorb heat, develop faster, and gain protection from predators. Each individual’s 10 cm diameter egg mass contains from 1000 to 3000 eggs.

Eggs laid now, in the cold infancy of spring, will mature slowly, over the course of a month. Later in the spring, when the water has warmed, the eggs may hatch in only 10 to 14 days. The amphibious parents have completed their responsibilities, though. They don’t stick around to provide care, cheer at baseball games, pay for dance lessons…

…Or teach their little tadpoles to ride a bike. Thankfully, I’m human!

As the frog chorus reverberated, I swung back onto my bike and continued around the lake. Wood frogs were only the beginning.

Not far from where I’d recently seen two otters on the ice, I spotted a sleek pair of loons in open water. With my ears now tuned in, the jingle bell chorus of spring peepers became apparent everywhere. Three stunning, black-and-white osprey perched on top of their nest platform (three!?) and swooped into flight as I approached. A bright orange fox with sleek new fur bounded through the ditch. As I slowed to look for more loons from a short bridge, the clear whistle of a song sparrow reached my ears.

All along the road, frogs croaked and peeped, robins whinnied, juncos trilled, and geese honked. Silence has gone out of style. Let the symphony of spring commence!

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 1, 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.

These remarkably terrestrial frogs spend most of the year in the woods, but wood frogs migrate short distances to woodland pools for mating in the spring. They are distinguished by their rakish black mask. 
Photo by Emily Stone.

Friday, April 15, 2016

Out on a Limb

Broken branches littered the road from a thrashing wind and rain storm the previous night. I paused occasionally from my walk to pull the bigger ones out of the way so they wouldn’t surprise unsuspecting drivers on the winding gravel road. After dragging a red maple branch—replete with swelling, crimson buds—to the shoulder, I noticed that the soggy gravel was still covered with the brightly-colored clusters.

Had all these buds been knocked off in the storm, too? But why would they remain united in their twig-tip clusters? I picked one up to examine it more closely. Two rings of buds encircled the tiny shoot, and the twig showed a neatly-clipped end. Something had bitten the twig off of the tree. The buds looked intact, though. Why would some creature go to so much effort, and then let it all fall to the ground?

I, too, dropped the cluster as I continued on my walk, but the problem still bugged me. Porcupines often feed on “nip twigs” like this—snipping a branch, then turning it around to access the edible parts—but a porcupine would have nibbled the buds off. Plus, I recently learned that porcupines almost never eat red maples because the plant contains too many acidic tannins as a defense. I’ve seen squirrels feeding on hemlock and spruce buds in this manner, too. But each little spikey green nip twig I recover from that snacking technique is missing its nutrient-packed terminal buds.

When the loop of my walk brought me back to the patch of maple buds on the road, I decided to look more closely. I’m glad I did. Although the buds looked undamaged from afar, when I looked closer, I could see that most of the buds had been gutted. The outer bud scales—bright red with white margins—were still mostly intact, but a single hole in the bud led to a hollow center. Perhaps the muncher was avoiding toxic tannins by only eating the tender embryonic leaves and flowers, and not their tough, protective covering.

A quick internet search revealed that yes; red squirrels, gray squirrels, flying squirrels, and fox squirrels all will eat red maple buds in the spring. No source mentioned that they hollow out the buds, but that’s I observed, and it makes sense as a technique to avoid excess tannins. If that’s true, then I would guess that squirrels have an advantage over porcupines in exploiting this niche—while squirrel teeth might be small enough to scoop the sweet centers out of tiny buds, porcupine teeth most likely are not.

Squirrels must be crafty in this is a hungry time of year, when their supply of fall nuts and seeds has run low, they need energy for breeding season, and extended cold has slowed the arrival of a spring bonanza. Soon (we hope) they will have more food in form of willow and aspen catkins, maple flowers, maple seeds, and even baby birds. Until then, I guess we’re all on the same boat…er, branch…waiting anxiously for spring.

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 3, 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.

These nipped-off clusters of red maple buds present a mystery to curious naturalists. My guess is that squirrels scooped out the tasty baby leaves inside the tough bud scales. Have you ever seen the culprit at work? Photo by Emily Stone.

Friday, April 8, 2016

Slushy Cold and Palm Trees

Slushy cold drink in hand, I took a deep breath and looked up from my book. Rows and rows of beach chairs stretched out in front of the one I had claimed, their geometric arrangement accented by regularly spaced palm trees. Through the trunks, past the white sand, and between brightly colored bathing suits, turquoise waves sparkled in the sun.

I was grateful for the shade of the palms (I think they were coconut palms), since the warm afternoon sun would have surely boiled my winter-thickened blood and crisped my pale skin to crimson. But the trees bothered me, too. Usually on vacation (usually in the Boundary Waters), I contemplate the tenacity of gnarled jack pines whose resolute  roots find the ingredients for life wedged deep inside bedrock cracks. How did the resort ever get palms to grow in pure, salty sand?

While my vacation in Playa del Carmen, Mexico, was filled with all the usual activities, I also experienced a fair amount of frustration. With little prior knowledge of tropical natural history (I tend to head north for trips), and no nature guides (paper or human) on hand, I felt lost. Next time I’ll do it differently, I resolved, but this time I still had to deal with the unusual experience of not understanding my environment.

Arriving home to internet access, I had many questions, but the problem of palm trees stood out. I knew they weren’t like maples or oaks, but why and how?

The essential difference is that maples, and many flowering plants that we’re used to, are dicots. When their seeds sprout, they produce a tiny pair of baby leaves, or cotyledons. Palms are monocots, and along with grasses, lilies, and asparagus, they only produce one cotyledon when their seeds sprout. The number of seed leaves is just the beginning—an easily visible character that actually indicates much deeper differences.

For one, the roots of palm trees don’t go deep. Instead of a sturdy taproot and woody lateral roots gripping deep into the bedrock crack, palm trees have a mass of small, non-woody roots that begin low on their trunk in the “root initiation zone” and extend to form a dense mat in the upper foot of soil. Instead of tapering toward the end, the roots of a palm stay the same diameter throughout their length. The roots visible around the lower trunk of many trees reminded me of a bowl of thick spaghetti noodles.

As it turns out, this root structure makes palm trees relatively easy to transplant, which explains how the resort could build itself a ready-made shade structure of mature trees. Not only are the root mats easy to manage, the trees have their own insurance against transplant shock.

Every year I cross my fingers when my tomatoes droop for their first days in the garden, as they struggle to get roots to water and restore turgor pressure to their cells. Palm trees can live off the water and carbohydrates stored in their trunks while the roots regrow.

That palm trunk arises from a single apical meristem, or cluster of undifferentiated cells where growth can take place. In a maple tree, meristems allow for branching, twig growth, and much more. A palm tree has no capacity for branching, and grows straight up, with its leaves also originating from the single meristem at the top of the stem. Old leaf bases cluster around the meristem in a bristly beard, which offers it some protection against cold, disease, trauma. If the apical meristem is damaged, the whole tree will die.

Maple trees also have a lateral meristem—the cambium—which grows new cells around the stem each year, thickening the trunk and forming the tree rings we know so well. Though stiff and sturdy, palm trunks aren’t truly made of wood, and the cells aren’t arranged in rings. Instead, its vascular system of xylem and phloem bundles is dispersed throughout the stem with no ring-like structure. The stem grows slightly wider and stronger, mostly through the thickening and strengthening of these cells as they age.

Because of the dispersed nature of palm trees’ vascular systems, they aren’t susceptible to girdling. In a maple tree, the vascular system is just under the bark, and if you cut it all the way around, water can’t flow, and the tree dies. With dispersed vascular bundles, water would simply continue to flow elsewhere inside the palm’s trunk. The tree might die of disease from such an injury, though. Palm trees don’t have the ability to grow scar tissue or repair damages, so any break in the bark-like cortex may allow in disease. In contrast, as maple sugaring operations prepare to pull their taps, the operators know that this year’s hole will soon fade under a healing scar.

The differences between sunny Mexico and spring in Wisconsin are extensive, and fun to think about. I’m glad to be home, but I do wish that the slush would stay placidly in my cup instead of falling from the sky.

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 1, 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.

Palm trees provide shade just like our maple trees, but they grow very differently.
Photo by Emily Stone.

Friday, April 1, 2016

Look to the Sky

Note: This article was originally published in March 2013. It is also the opening chapter in my new book, “Natural Connections: Exploring Northwoods Nature through Science and Your Senses,” which is being published this spring.

Crusty snow crunched loudly under my skis as I powered up a hill. My arms burned as I compensated for the chunky, uneven, spring snow. All my concentration focused down on the gray snowpack and inside my core.

Then I reached the crest of the hill and looked up. Blue sky and bright sun filtered through every gap in the trees. My mood lifted.

I am a naturalist, not a philosopher or religious scholar, but it seems to me that in both religion and nature we look to the sky for assurance that rebirth will occur. In springtime especially, prayerful folks are lifting their eyes skyward to thank a higher power for a certain ancient resurrection. When the world around us is gray and cold, and it seems like spring might never come, a look to the sky reassures us. That deep, blue color; the lengthening days; and the intensity of the sun all signal that the ancient rebirth of spring, however slow, is on its way.

Earlier last week, damp cold permeated the silent woods. Dark trees stood somberly, the live ones indistinct from the dead. I trudged on in melancholy monotony. Suddenly I became aware of my mood and the tunnel of gray that had ensnared me. To break free, I looked to the sky and felt hope return.

During these gray days of early spring, when food is scarce for many in nature, they still put all their energy into creating new life. Squirrels, who have resorted to eating bitter spruce buds, are chasing each other in a frenzy to reproduce. Foxes and fishers, who might have trouble breaking through crusty snow to access mice, are traveling widely to defend their breeding territories. Whitetail does and mothers of all kinds are nurturing their unborn young with the last reserves of their own bodies.

I understand the warblers who return in the warmth of spring to feast on our plentiful insects and raise their young in the bounty of summer. It is harder to comprehend the skunk who must rouse himself out of his warm burrow in the early dawn of spring and traipse across a frozen landscape with the intention of creating new life. How can he even be sure that nature will provide warmth and food again?

Animals have this faith built right into their genomes. You might call it instinct or adaptation.

Plants who stored starches in their roots last fall, carefully prepared buds many months before spring, and crafted nutrient-filled seeds in the dog days of summer also have this faith.

Insects are waiting patiently, too. Long ago in the shortening days of fall, they found a protected place to hide. Some overwinter as adults, some as larvae or pupae, and some as eggs. The individual may not survive, but the cycle of life continues.

Underneath two feet of dense snow lies a carpet of aspen leaves with little green islands where moth pupae wait for spring. Inside goldenrod galls, the fly larvae have not yet pupated and still risk death at the piercing beak of a downy woodpecker.

Ticks will soon become active in widening patches of bare, sunny, forest floor.

Wood frogs, still frozen under the snow, are poised to thaw at the first chance. Spotted salamanders wait in their tunnels below the frost line. Their cells contain little bits of algae who are waiting to emerge into the sunlight and begin photosynthesis.

Loons are in their breeding plumage and have started moving north. They will fly to the edge of winter and make forays each day to check on the progression of ice-out. Turkey vultures have already arrived.

If you, too, feel that tunnel of gray ensnaring you, just look to the sky. The cycles of spring restore our faith in the power of life.

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 1, 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.

Look to the sky and you might catch a glimpse of something lovely, even if it is only more water against the gray dampness. Photo by Emily Stone.
Illustrations for my upcoming Natural Connections book were crowd-sourced to students and friends. Stacy Craig captured the mood of my opening chapter with this lovely sketch. 


Friday, March 25, 2016

Red-winged Blackbirds

When springtime starts with sloppy mud, gray skies, and tepid weather, it’s hard to get excited about the season. No sound is better able to pierce this wet blanket than the ringing konk-la-ree call of a red-winged blackbird with its thrilling trill at the end. I’ve heard it everywhere lately, from a lakeside bike ride to my walk from car to office.

Red-winged blackbirds are year-round residents in much of their range, which stretches from the Yukon down to the Yucatan. The northern breeders, though, must migrate far enough south to find crop stubble with waste grain and weed seeds not buried by snow. They gather in large flocks of as many as several million birds, and fly up to 50 miles each day from the roost to foraging grounds.

For red-winged blackbirds in the Great Lakes region, this generally means about a 700-mile trip. That’s not far in comparison to our “neotropical” migrants like hummingbirds, flycatchers, thrushes, and warblers who fly thousands of miles to overwinter in Central and South America. Those birds are nectar or insect specialists, and can’t eke out a winter survival on seeds alone.

One advantage that staying in the neighborhood gives red-winged blackbirds is that they have a better idea of how this particular spring is progressing, and can adjust their migration schedule based on weather. Neotropical migrants have no way to tell that spring is coming early in the north, so they stick to more stable cues—like day length—to decide when to migrate. Weather still affects their progress, since a winter storm or unfavorable winds can cause a delay, but their timing tends to be more consistent.

Red-winged blackbird males overwinter even closer to home than the females, because they have good reason to get back north as early as possible. The first male often gets the best territory, and it’s their gloom-piercing call that seals the deal. Belligerent males display in a “song spread” that includes fluffing up feathers, spreading their tail, raising their shoulders, and flashing their red epaulets, all while singing at the top of their lungs. We may appreciate this colorful performance, but it is not friendly, and it is not for us.

While the flocks of males currently foraging in yards and under bird feeders are not on territories yet, they already singing loudly—warming up for the big show. Drab, brown females will follow later, after insects begin to hatch. The ladies need a high-protein, high-calcium diet to prepare for egg laying, and have no reason to risk getting caught in a blizzard.

Once they arrive, females will choose a male’s territory, and set up a smaller territory within it. As many as 15 females might nest in a single male’s territory, but the average is five. Nests are built low to the ground, and are suspended among some upright stems of marsh plants. Females wind stringy plant material, wet leaves, and decayed wood into a bowl, and the line it with soft, dry grass.

This habitat requires a couple special adaptations. The most visible is the brown-streaked plumage of the females—perfect for staying camouflaged in the thickets. Those feathers are also extra sturdy, because living among rough cattail stems could result in undue wear and tear. In addition, both sexes have sturdy leg muscles that allow them to perch with each foot on a different cattail and do the splits.

Red-winged blackbirds also have long digestive tracks, which allow them to eat a wide variety of foods. In the summer, though, when their diet focuses on insects, their gizzards will shrink, only to get more muscular again when late summer seeds become ripe.

Late summer seems worlds away, though, as snow falls in the mud puddles and weed seeds get re-buried. The migrating flocks of red-winged blackbirds must be on the move again, looking for spring. When they find it, we can be sure they’ll sing a ringing konk-la-ree to let us know.

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 1, 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.
Red-winged blackbirds are an early spring migrant, and pierce even gloomy days with their ringing call. Photo by Larry Stone. 

Friday, March 18, 2016

Hot and Cold for Spring

During the fickle days of early spring, my emotions seem to rise and fall in sync with sap in the maple trees. I get kind of grumpy when the mornings dawn damp and cool and the tracks on the ski trails sink dejectedly into the slush. After the extended ski seasons of the past two years, I’ve gotten accustomed to having endless days to explore new trails and perfect technique.

My feelings change as the days brighten, intense sun takes over, and the temperature spikes. Warm breezes and dry roads make me eager to put away the skis, and happy to pull my road bike out of storage. I guess you could say that I’m running hot and cold for spring.

The first place I head on my inaugural spring bike ride is to a little wetland across the county road from Lake Namakagon. This wetland tends to thaw a bit sooner than the one by my house and it is consistently the first place I hear the spring chorus of frogs.

The eleven species of Wisconsin frogs (and one species of toad) wake up and begin singing their songs in a typical order each spring. Their specific phenological timelines depend on things like overwintering location, cold tolerance, and breeding habitat.

Our three earliest singers share some common characteristics. Wood frogs, chorus frogs, and spring peepers are all somewhat terrestrial frogs that spend the winter as frogcicles, buried lightly in duff on the forest floor. Spring sun and warm rains can reach them quickly here, and they are triggered to thaw, wake up next door to their honeymoon suites, and breed very early in the season. April is typically their main month of romance, but each spring progresses a little differently.

By getting such an early start, these frogs are able to carry out their entire breeding cycle in vernal pools. These woodland puddles only persist for a few months each spring. This means that eggs and tadpoles don’t have to worry about the fishy predators who would live in a permanent body of water, but it also means that the parents need to hurry up and get their babies growing so that they can gain legs before the pool dries up.

Of course, spending winter on land has its own challenges. Even though the subnivean layer—where snow meets earth—remains warmer than the television weather report, frogs in the duff must still endure below-freezing temperature for many days at a time. They do this not by avoiding the frogcicle state, but by guiding it.

Wood frogs are the most highly studied, but spring peepers and chorus frogs use similar techniques. The process starts early in fall, when wood frogs begin accumulating urea in their tissues. While urea is a waste product that humans excrete in our urine, urea is also a cryoprotectant, or a substance used to protect biological tissue from freezing damage.

Then, when the temperatures dip below 32 degrees Fahrenheit, ice crystals start to form on the frog’s skin. Some animals are able to “supercool” or prevent the formation of ice even when temps dip below freezing. This usually requires them to avoid contact with ice that would trigger flash freezing. Frogs, with their permeable skin, just allow the frost to set events in motion.

Ice formation causes the frog’s liver to convert stored glycogen into glucose. The sugar floods throughout the frog’s body, carried in its bloodstream by a heart that keeps beating as long as possible. As ice forms outside of cells, it locks up the pure water, and leaves behind a higher concentration of salts and other things that were previously dissolved in the liquid. Water from inside the cells wants to flow outward, across the cell membrane, to even out the imbalanced concentrations.

This could dangerously dehydrate the cells, though, and there is a threat of them collapsing. Glucose and urea help the cells retain water in two ways. First, sugar water freezes as a lower temperature than plain water, and so less ice forms overall. Second, by increasing the concentration of chemicals inside the cell, it keeps water from wanting to flow out of the cell under osmotic pressure.

While frozen, the frogs are essentially dead.

Once spring comes, however, wood frogs thaw from the inside out. The heart starts beating (scientists still don’t know what jumpstarts it), the brain wakes up, and finally legs move. And those legs will carry them directly to a nearby vernal pool. A deafening chorus of love songs ensues, and mating commences in a hurry. Wood frogs quack, spring peepers jingle like bells, and chorus frogs imitate a finger plinking a plastic comb.

That’s what I was hoping for today, but the wetland was still quietly blanketed in snow. Over the winter, the frogs may undergo multiple freeze-thaw cycles. Springtime warmth also ebbs and flows. And then there’s me, sometimes turning a chilly shoulder to our next season, and sometimes embracing it with an open sweater. I guess I’m not the only who runs hots and cold!

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 phenology exhibit: “Nature’s Calendar: Signs of the Seasons” will open May 1, 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.

Wood frogs are hardy winter hibernators and early spring singers. You can identify this small brown frog by the black bandit mask across its eyes. Photo by Michael Zahniser, Wikimedia Commons.