Thursday, February 25, 2021

Curiosity, Perseverance, and Life

There’s a space kid inside almost every one of us. That fact is made clear to me by the nation’s giddy response to NASA’s most recent accomplishment—a successful landing of the Perseverance rover on Mars. The rover used a heat shield, a parachute, cameras, and a rocket-powered jetpack to land. Actually, the jetpack allowed the main contraption to hover while the rover was lowered gently to the surface on a cable. Whaddya wanna bet that next summer there will be kids making rocket noises while they drop the requisite bucket-on-a-rope out of their treehouses?

Perseverance Touching Down on Mars (Illustration): An illustration of NASA’s Perseverance rover landing safely on Mars. Hundreds of critical events must execute perfectly and exactly on time for the rover to land safely on Feb. 18, 2021. Credit: NASA/JPL-Caltech.

While that bucket is probably hoping for a delivery of cookies, Perseverance is looking for signs of life. Its landing area includes a delta—which is a place where a river carrying sediments from its entire watershed flowed into a lake, slowed down, and dropped most of its load in a fan-shaped landform. If there was life on Mars, surely signs of it would have been collected by the river and deposited here. The shoreline of the lake could be another hotspot, based on what we know about life and fossilization here on Earth.

Using another trick straight out of our 10-year-old dreams, scientists can tell the rover to shoot a laser beam at any promising rock and then analyze the chemical composition of the dust cloud that rises. If the rock warrants a closer look, then an x-ray beam and another laser will take a peek at the chemicals present. In the most promising spots, the rover will drill down and collect a piece of the planet. What then? The sample will be stored in a box full of neat rocks (who among us doesn’t have one of those in the basement or garage?) that a future mission of the European Space Agency will bring back to Earth.

Signs of life could include minerals that don’t tend to form on their own, or structures that often form in the presence of critters. There’s an example of one of those structures on Old Grade Road northeast of Lake Namakagon. The Grandview Boulder is taller than a person, and under the moss you can see thin, convex layers in the rock. These layers are the fossilized remains of colonies of photosynthetic microbes. The algae and cyanobacteria excreted mucus, which trapped sediment and eventually built their own rock—called a stromatolite.

The Grandview Boulder near Lake Namakagon exhibits thinly layered structures that scientists are now looking for on Mars. Photo by Emily Stone.

Stromatolites are common in the fossil record on Earth, but rare to find still living. And while discovering a rock with this pattern on Mars would be exciting, it isn’t a sure thing. Stromatolites can also form without the help of life.

So, it’s going to take something pretty special to give scientists complete confidence that they’ve discovered extraterrestrial life.

There’s another problem, too. What if life on Mars looks so different from life on Earth that we don’t even recognize it?

I tackled this problem myself once, as a middle schooler at Girl Scout Camp. The Girl Scouts had a partnership with NASA, and one of the activities they provided was a variation on an activity often called “Create-A-Creature.” Each girl was assigned to a different planet and given a description of the habitat there. All rock, all gas, no atmosphere, crushing gravity, toxic chemicals—there was a stunning array of characteristics among our planets and their moons. Next, we were given a box full of bottles, cans, yogurt cups, and all manner of random stuff scavenged out of the recycling bin, plus glue, pipe cleaners, and other standard craft supplies. The goal? Create a creature with adaptations that allow it to survive on our assigned planet.

Our assemblages of detritus didn’t look like much in fact, but in our minds they had rock-crushing teeth, sulfur-digesting guts, and all sorts of fantastical adaptations that have not yet evolved on Earth. That combination of crafts, space, and tons of imagination was a winning combination for the child that was me. Honestly, the space part wasn’t why I loved it, but the other two ingredients won me over.

I have since led this activity with my own students in many forms. On “Tidepool Day” in California, for example, we built sea creatures using both trash and natural objects scavenged from the wrack line left by high tide. And yesterday, just hours before the Perseverance landed, I led 5th graders in creating their own special fish during a Virtual MuseumMobile visit.

Because we don’t really know what life on Mars would look like if it did, in fact, exist, those NASA scientists need a special combination of skills and imagination. Waddya wanna bet that those NASA scientists and engineers were once kids who created things out of the recycling bin, made rocket sounds in treehouses, collected buckets of neat rocks in their garage, and crick stomped in rocky streams?

Waddya wanna bet that the NEXT generation of NASA scientists is doing those things right now?

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.

Thursday, February 18, 2021

Subnivean Party

Kerflumpf. Mumpf. Fump. It’s difficult to describe exactly the sound that snowshoes make in 18 inches of fresh, fluffy snow. I can tell you that the soundtrack includes some huffing and puffing, and the swish, swish, swish of nylon sleeves as arms swing their assistance. At the start of our recent dive into the polar vortex, I traded skis for snowshoes and headed out into the untracked forest.

Only snow-plops blown out of treetops marred these smooth drifts of snow.
Photo by Emily Stone.

The woods felt peaceful and serene. Only snow-plops blown out of treetops marred the smooth drifts. Winter, I thought to myself, can feel pretty lonely sometimes. If only I was smaller…

Because, for the little critters at least, there is a party going on under there. Under where? In a curious space called the subnivean zone.

Do you remember the magic of hoar frost that I wrote about a few weeks ago? Water vapor in the air crystalizes directly into ice without going through the liquid phase. Under the snow, at ground level, the opposite happens. Latent heat from the earth—stored months ago during days of summer sunshine—gives snow crystals at ground level just enough energy to vaporize back into their gaseous form. Sublimation is the scientists’ term.

The vapor rises just a bit, filtering into the snow, where it changes the structures of crystals as it solidifies again. The result is a zone of airy pockets and loose, granular snow topped by an icy ceiling; and above that a thick, insulating blanket made—counterintuitively—of ice and air. Best of all, this magical space remains at or near freezing. That might not usually seem warm, but after our weeks of subzero temps, we can probably agree that 32 degrees Fahrenheit sounds fairly pleasant.

I’ve written and taught about this subnivean zone many times before. Usually my focus is on the small mammals—mice, voles, and shrews—who make their winter homes in tunnels sewn between soil and snow. And, of course, there are the charismatic carnivores who chase those warm nuggets of protein. Short-tailed weasels (who become ermine in their white winter fur) follow mice directly into their dens. Foxes and owls take another route—pinpointing supper with their ears and then plunging in from above.

But I mentioned a party going on under the snow, and these are only the most visible revelers. Jon Pauli, a winter ecologist from UW-Madison, explains that, “In this refuge, there's a complex ecosystem of interacting microbes, insects, plants and animals that we can't see but are active throughout the winter.” In fact, says one of his research papers, the subnivium is where the “majority of biodiversity in northern temperate areas spends the winter.”

For example, Pauli and his colleagues have been studying the impacts of warming winters on the energy budget of wood frogs. These cold-blooded amphibians take refuge in leaf litter and very carefully allow themselves to freeze solid while the subnivean zone forms around them. Once frozen, their metabolisms are shut down, which preserves their limited energy stores. The moderating effects of the subnivium buffer them from energetically costly freeze-thaw cycles, and also reduce the potential for lethally low temperatures.

Frozen wood frogs have a fair amount of company. One group of ants, in the genus Temnothorax, likes to set up house inside empty acorn shells. Like a colonial version of hermit crabs, they compete for a limited number of good homes. Loathe to abandon their nut hut for the winter, they simply snuggle up with about 100 workers and a few larvae and produce glycerol as an antifreeze to prevent cell damage. Unsurprisingly, colonies in acorns that are buried more deeply in the leaves and soil have higher winter survival rates. Also unsurprisingly, the little girl in me loves that nature has its own version of acorn fairies.

Temnothoraz ants are also known as “acorn ants” because their colonies live inside acorn shells. Photo by Matt Hamer, Wikimedia Commons.

A thick layer of leaf litter isn’t just important for ants. Autumn leaves provide insulation before snow accumulates, and then continue to augment our fluffy white blankets. This protects plants’ roots from freeze damage. Dead leaves also provide essential habitat for woolly bear caterpillars, mourning cloak butterflies, luna moth cocoons, the eggs of red-banded hairstreaks, bumblebee queens, spiders, snails, millipedes, mites, and more. Some of them are frozen, some of them are active. And they aren’t the smallest subnivean inhabitants.

Woolly bear caterpillars need thick leaf litter covered by insulating snow in order to survive the winter. Photo by Emily Stone.

The microbes that Pauli mentioned are important here, too. Fungi and bacteria take advantage of the microclimate of the subnivean zone to slowly break down dead stuff throughout the winter. They release their nutrients in spring—just in time to fuel the growing season. In contrast, invasive earthworms decimate the leaves too quickly. Both insulation and nutrients diminish.

As I was saying, the soundtrack above the snowpack is pretty quiet. That allows me to cock my ears like a fox and focus my listening toward a hidden world beneath the snow. What do I hear? A wild party in that magical place we call the subnivean zone.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.

Thursday, February 11, 2021

Patterns of Life: Galls

Summer in the Northwoods can feel like a painting—broad sweeps of green and blue provide the backdrop for highlights in all colors of the rainbow. Winter, though, can feel like a pen and ink sketch, where shapes, textures, and patterns rule. I enjoy these shifts in perspective, since they can help me spot new things.

A little while ago I found myself in a weedy strip of vegetation between my friend’s driveway and a field. The colors of summer had all but drained from the thicket of goldenrod plants. Where once there were sunny yellow flowers tossing above a sea of green leaves, there now stood a sepia-toned jumble of fuzzy seed heads, crinkled leaves, and leaning stems. In this winterized sketch, I scanned the lines, looking for a particular pattern.

Goldenrod galls are small, round lumps that appear near the tops of the growing stems in response to the chewing action of insect larvae. Every year I collect a couple gallon bags full of these galls to use in our MuseumMobile lessons. With kitchen shears in-hand, I had soon accomplished my goal.

Many of the galls were the typical, spherical homes of goldenrod gall fly larvae. But as I started sorting through and cutting them open, I found one that didn’t match. It wasn’t much different—only slightly taller than wide, with some raised ridges. I knew that its real differences were hidden inside. A sharp knife around the equator of the gall soon revealed a hollow center with a shiny brown shell rattling around. The shell was the dried out puparium (like a chrysalis) of the goldenrod gall moth—Gnorimoschema gallaesolidaginis—whose larva created this elliptical gall.

An elliptical gall formed by a gall moth on a goldenrod plant. Photo by Emily Stone.

As I rolled the thin, mummy-like shell in my fingers, it cracked open. The split did not reveal a metamorphosing moth pupa changing from larva to adult. Instead, dozens of tiny, white, translucent larvae—each only about 2 mm long—spilled out of the hollow cylinder. Any normal person would have been grossed out. I was thrilled! The moth larvae are parasites on goldenrod, and they themselves are victims of many different parasites. I wrote about this in 2017, when all I found was a hollow, hole-riddled shell, cleaned out by the larvae of a tiny wasp.

The shiny shell of a gall moth puparium—only 2 mm in diameter—cracked open to reveal a mess of tiny parasitic wasp larvae that ate their host. Photo by Emily Stone.

Based on some research and inquiries, these translucent larvae probably belong to a different species of tiny, parasitic wasp. While wasps like these can’t sting us—their ovipositors are just for depositing eggs—they do play an enormous, and largely hidden, role in our ecosystems by keeping the populations of other insects in check.

I currently have some of the larvae tucked away in a Mason jar with a damp paper towel in the hope that they will metamorphose into adults and give us more clues as to their identity.

In the meantime, I found another curious pattern in the lines of my winter woods.

On several snowshoe hikes recently, I’ve gazed up at the lace of bare branches silhouetted against the sky, and found one tree among them covered in lumps. While these woody balls persist through the summer, they are out of sight and out of mind—hidden by that wash of green.

Like the lumps on goldenrod stems, I figured that these were probably galls. Plant galls are simply abnormal outgrowths triggered by everything from viruses, fungi, bacteria, insects, and mites, to other plants. Which of those parasites could trigger such persistent, woody galls?

Rounded galls caused by a fungus dot the branches of a northern red oak tree. Although a red maple’s twigs are intertwined, it does not seem to be infected with the fungal parasite. Photo by Emily Stone.

The answer, according to a fact sheet from the Wisconsin DNR, is that these galls are caused by a fungus in the genus Phomopsis. While little is known about how the fungus spreads, it seems to start on the smallest twigs before moving to larger branches. Often, only a single tree or a small cluster will be impacted. Some twigs or branches may be girdled and die, but the main tree will survive for many years. There is no treatment available, or even needed, although you can cut off infected branches if you find them unsightly. I find them whimsical!

While I’ve mostly noticed Phomopsis galls on northern red oaks, they also occur on maples, hickories, and other species in Wisconsin. Around the world, the fungus causes galls on trees in Italy, Poland, Spain, Portugal, Switzerland, England, India, Russia, Tunisia, and more. (This list is gleaned from the titles of scientific journal articles written about the fungus, but could also serve as my post-pandemic travel goals.)

The austere sketch of winter reveals many patterns. We see lines…and lumps where lines should be. We see the patterns of lives interwoven.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.

Thursday, February 4, 2021

Like a Rifle to my Dreams

I opened my garage door and gazed out toward the setting sun over an expanse of snow-covered ice. Strange, I thought. The lake level must have risen, since the ice was now level with the sill. Turning to the right, my heart jumped when I saw two young polar bears playing in the snow just meters away. They were white, fluffy, and cute. Although their body shape was wrong. Maybe they were albino black bears? In any case, they paid me no mind, and seemed to present no danger. But, where was their mother? Then CRACK! A sound like a rifle shot reverberated through the air.

I awoke with a start and opened my eyes to the dark room. The bears had been in my dream (where did that come from!?), but the sound was from real life. I fumbled through a sleepy haze to understand the noise. Was the house falling apart? No, there were no other sounds of destruction or chaos. Then, obviously, it must have been a tree cracking open in the cold.

I checked my phone: 3:30 a.m. I opened my weather app and checked the temperature: -13 degrees Fahrenheit and falling. Outside, a full moon cast shadows in the brittle cold. “Sweet,” I thought to myself as I rolled over, “now I know what to write about this week.”

The thermometer read -18 degrees when I came downstairs to make coffee. This had been one of the coldest nights of the winter so far, and it followed on the heels of a really lovely, clear, sunny afternoon. At one point I had turned my face to the sun and reveled in the warmth I felt—even though the high temperature only reached 11 degrees above zero.

My face wasn’t the only thing absorbing warmth. The low-angled rays of afternoon sun were beaming their energy onto the southwest sides of trees. This heats up the bark and the inner wood. When things warm, they expand.

The other side to that, of course, is that as the Earth’s heat escaped into a cloudless night and temperatures plummeted, the wood contracts rapidly and unevenly, with the outer layers showing the most dramatic change. The contrast is divisive, and the sound of wood ripping apart is loud.

Even as it burst into my dreams, the past night’s crack had sounded close. So, once the temperature rose above zero, I layered up and decided—without much hope—to see if I could find the tree who split. Standing under my bedroom window, I turned to look northeast—at the southwest sides of the trees—the side that usually cracks. Sure enough, there were at least a half a dozen narrow scars snaking lengthwise up trunks. On ashes, maples, and hemlocks, these cracks had all been trying to heal themselves for years if not decades. These were good evidence of past frost cracking.

On snowshoes, I took a little tour of the scars. They were filled with rough bark, old mushrooms, beetle-hole-riddled wood, piles of sawdusty larval frass, crusty specks of wound-healing pitch, and the messy webs of now-frozen spiders. Wonderful stuff, really. These old tree scars are fun to explore!

The scar from an old frost crack.

Old mushrooms

Beetle larvae frass (poop) that is basically sawdust.

Spider webs

Want to learn more about these and other Unsung Heroes of Nature? I'm giving a talk on February 11, 2021, for the Master Gardeners, and everyone is welcome! 
Find more info and the registration link here.

As I came full circle, though, the black stripe of a narrower crack caught my eye. It was on the southwest side of a young basswood tree—less than a foot in diameter—and just beyond my bedroom wall. Close up, I found none of the scar tissues or evidence of age I’d seen in the other scars. Instead, I found the warm brown colors of bark that hasn’t been weathered. I found small slivers of creamy wood—freshly exposed. And I found a deep crevasse filled with glittering crystals of hoar frost—assembled from moisture recently released from damp wood.

Some previous injury weakened this young basswood tree, and then plummeting temperatures caused it to crack open with a sound like a rifle shot. Photo by Emily Stone. 

Freshly exposed wood and hoar frost in this crack give clues to just how recently the fissure opened. Photo by Emily Stone.

When this frost crack opened, humid air inside the wood made contact with frigid temps, and hoar frost crystals grew. Photo by Emily Stone.

Freshly exposed wood and hoar frost in this crack give clues to just how recently the fissure opened. Photo by Emily Stone.

Radial cracks like this one—fissures that dive inward to the tree’s core instead of just separating inner bark from outer bark—are associated with injuries sustained in the tree’s youth. Did some piece of equipment scrape against this young basswood 20 years ago as the house was being built? The injury creates an area of weakness, and an entry for decay. Bacteria and fungi move in, and as they decompose the wood it absorbs extra moisture. The defective wood doesn’t expand and contract as well as healthy wood, and rapid freezing finally bursts open a significant crack. CRACK!

Warm weather will allow the wood to relax and close the crack again. The tree will begin to build scar tissue around the injury. And maybe, with quieter nights, I’ll get to enjoy the antics of those polar bear cubs.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.