Cold Trees Have Teeth

The rustling of paper mixed with the rustling of wind in the trees as eight adults slipped birch leaves between the sheets on their clipboards and began to rub. Like magic, the sides of their crayons revealed a prominent midrib with thick veins branching off at acute angles and a network of finer veins filling in the space. The teardrop-shaped leaf was defended around its perimeter by a row of sharp teeth that—if made of metal—would probably work better than my current bread knife. “Paper birch,” the students wrote next to their delicately rendered crayon artwork.

One of my college professors lauded leaf rubbings as “good data,” and my field notes from that class are a mix of colorful crayon smudges, penciled notes in shaky, on-the-fly handwriting, and wrinkled dots made by raindrops. That class was my first big step toward being a naturalist. Remembering this, I wasn’t bothered by the bemused smiles I got when I handed out crayons to participants in the Museum’s recent Tree and Shrub Identification program.

As we walked around the Museum’s backyard, and then the river landing, and finally a ski trail, a pattern began to emerge in the leaf rubbings. We looked at maple leaves with their big lobes; red oak leaves with prominent lobes and pointed tips; and basswood, ironwood, musclewood, cherry, ash, and aspen all with finely serrated leaf margins.

A few of the shrub species in the understory had un-toothed, un-lobed leaf margins with a smooth line that botanists describe as “entire,” but the program ended before we got around to identifying them. The vast majority of leaves we walked past had teeth.

That’s not the case everywhere. When I explored the jungle of Costa Rica with a Museum group a couple of years ago, we saw mostly smooth margins on the leaves that arched over the pathways and framed the wild colors of scarlet macaws, chestnut mandibled toucans, and collared aracaris.

A chestnut-mandibled toucan eats berries among leaves with smooth margins in Costa Rica. Photo by Emily Stone.

A collared aracari perches among leaves with smooth margins in Costa Rica. Photo by Emily Stone.

Why the difference?

Well, take just a second to think about the major differences between Costa Rica and Cable, Wisconsin. The first one you probably thought of is correct: temperature. Colder regions have more teeth on the leaves of their woody plants, and warmer regions have more shrubs and trees with smooth leaf margins. The difference is so pronounced, so measureable, and so constant, that paleobiologists can use the prevalence of teeth on fossilized leaves to estimate the climate of the forest they grew in, millions of years ago.

Leaf teeth matter, and change, on much shorter timescales, too. In one experiment, scientists planted seeds from the same maple tree in two locations: Florida, and Rhode Island. Leaves on the seedling grown in relatively chilly Rhode Island had deeper lobes and more teeth.

So, mean annual temperature, that’s one answer to the question of “why?” But go ahead, channel your inner three-year-old, and ask it again. “Why?” Why do colder climates produce toothier leaves? Why would it benefit a tree in Wisconsin to have deep lobes? Why is a tree in Florida or Costa Rica better off when it has smooth leaf margins?

Through more experiments, scientists found that the edges of leaves are where a lot of the action happens, especially in early spring. During the first few weeks of the growing season, as leaves are unfurling, scientists have measured an increase in gas exchange—a sign of biological activity, just like you breathing hard after a run—from the teeth.

All of those little edges are busy taking in carbon dioxide, releasing oxygen, and letting water vapor escape at the same time. Water vapor exiting the leaves—called transpiration—pulls more liquid up from the roots like someone sucking from a straw, and that boosts sap flow. That sap is full of nutrients that the young leaves can use to expand and ramp up photosynthesis. It jumpstarts the growing season.

In our cooler climate, with plenty of precipitation and a short growing season, trees can afford to lose some water in order to speed up sugar production. In warmer climates, toothed leaves might cost more water than the tree can afford, and therefore smooth margins prevail.

In places where winter comes with biting cold, it’s actually the trees that have the teeth!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Butterflies Live in Layers

Every afternoon, the Museum’s pollinator garden draws me outside with the magnetic pull of its beauty, and the possibility of discovering something new.

I’m rarely disappointed.

This week, while following the darting flights of a calico pennant dragonfly, a weird pattern caught my eye. On a knee-high plant, a few narrow, pointed leaves had been laid up against the stem and wrapped in webbing. They looked a little worse for the wear. If the holes in milkweed leaves can tell you where to find monarch caterpillars, then this web probably held something interesting, too.

I didn’t have to get much closer to see a swarm of dozens of tiny caterpillars feeding on the leaves, with some staying protected inside the web tents. Despite their tiny size, clusters of bristles erupting from nodes all around the caterpillars’ body segments made them seem rather stand-offish. In translucent shades of cream and brown, they weren’t much to look at.

Still, after a few photos and a visit to iNaturalist.org, I had a name for them: Harris’s checkerspot. These were the larvae of a pretty orange butterfly with black markings—smaller, and softer-looking than a monarch. In order to be sure, I also had to identify the plant they were eating. My PlantNet app, and the Minnesota Wildflowers website, both helped to confirm: flat-topped white aster, Doellingeria umbellata. This is the only food in the entire world that this species of caterpillar can eat.

These small, rough hairs on the leaf margins--so small that my fingers could feel them but only my macro camera could actually see them--were one of the key identifying factors for flat-topped white aster...especially because the caterpillars will never give this particular plant the chance to bloom! Photo by Emily Stone.

Of course, that’s not terribly unusual. Monarch butterfly caterpillars can only eat milkweed. Rosy maple moth larvae focus on maple trees. Aphrodite fritillary caterpillars munch only on violet leaves. Oil bee larvae can only develop on a diet of floral oil and pollen from loosestrife flowers.

Adult Harris’s checkerspots are not nearly so picky. They sip nectar from a bounty of blossoms. In contrast, hairy-banded mining bees (who were featured in our Bee Amazed exhibit a few years ago) specialize in foraging on goldenrod flowers. They won’t even emerge from the ground nests where they overwintered until their favorite flowers bloom in August.

With all of these picky eaters and close relationships in the world of pollinators, the diversity of native flowers in our pollinator garden is what really makes the difference. Each insect can find something it needs as both a larva and adult, and each flower can attract someone to move its pollen. Plus, with so many different flowers, we have something blooming all the way from early spring into late fall.

This week, something else caught my eye. Heather Holm, author of “Pollinators of Native Plants,” and an expert advisor on our bee and pollinator exhibits, posted two new graphics to Facebook. One of the beautifully drawn, four-paneled handouts talks about keystone species, which means plants like oak trees that are food for at least 940 species of caterpillars.

The other graphic introduces the concept of “soft landings.” Heather’s website explains that, “Soft landings are diverse native plantings under keystone trees (or any other regionally appropriate native tree). These plantings provide critical shelter and habitat for one or more life cycle stages of moths, butterflies, and beneficial insects.” She’s advocating for people to use the tree’s own leaves to build up soil and duff around its trunk, and add shade-tolerant native plants to create a cradle for those caterpillars to fall into when it’s time for them to pupate or overwinter. “It’s a great place for a beginner to start making a difference in their own yard,” Heather told me.

Funded by a grant from Wild Ones Minnesota. ©2021 Heather Holm and Neighborhood Greening. Developed in consultation with Desiree Narango, Ph.D.; artwork by Elsa Cousins. * For more on creating soft landings under trees, visit: www.PollinatorsNativePlants.com/softlandings.html

If you’ve been to our Mysteries of the Night exhibit, you know that this habitat could benefit fireflies, too!

I’ve been learning about and teaching about leaf litter and “messy” yards as good habitat for a while, but this was the first time I really saw the life of butterflies and other insects in layers. First there’s the canopy of flowers that provide nectar for the adults, and pollen for baby bees. Then there’s the understory of leaves—which might actually be overhead—that the caterpillars need to eat. And finally, the ground layer of loose soil, dead leaves, and rotting logs is essential for these insects to complete their life cycles and survive the winter.

“Plant diversity will yield butterfly and moth diversity,” Heather reminded me. And that includes the dead and rotting plant parts, too! For example, the Harris’s checkerspot caterpillars that first caught my eye this week overwinter as large caterpillars in the duff under their favorite aster—ready to resume feeding again in the spring, before pupating and emerging as a butterfly in late June.

I’m going to make sure that our “messy” pollinator garden continues to attract a diversity of life, and provide all the layers of habitat they need to live.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Sparkling droplets of baby food and Tyvek

As I wheeled my bike past the front gardens at the Museum, the heady perfume of common milkweed flowers swirled in the deepening shade of late afternoon. A monarch butterfly landed, sipped nectar from the pale pink flowers, and then rose easily with flaps of its enormous, orange wings. Little black ants crawled industriously over the blossoms, too. Tonight, after I’d sunk into bed, these pale, sweet smelling flowers would likely send out their beckoning signals to the night shift—moths looking for a sip of sugar-filled nectar on their way to find a mate.

Ten miles later, as I entered the dim tree tunnel of my town road, I smiled at a patch of yellow stars twinkling from the gravely shoulder. The five-petaled flowers belong to fringed loosestrife, a native plant that seems to be on the increase along roads where I ride my bike.

Fringed loosestrife is a native plant with yellow flowers. It often grows in damp soil. Photo by Emily Stone.

If you live on a lake or pay attention to invasive plants, the name loosestrife might send a shudder down your spine. Purple loosestrife is an introduced species that is listed as “Restricted” in Wisconsin, which means that “it has the potential to cause significant environmental or economic harm” when it fills in wetlands, replaces native plants, and disrupts habitat for fish and wildlife.

Luckily, these two plants are unrelated by both taxonomy and ecology. They are in two completely different plant families, and fringed loosestrife does not become invasive. The shared name doesn’t seem to have any botanical significance, since it’s a literal translation of Lysimachus, the name of a friend of Alexander the Great.

There were no butterflies flitting in their unsteady way among these flowers, though, and neither would fur-covered moths drink from sweet chalices by night. A closer look at the blossoms—through the macro setting on my camera—revealed hundreds of tiny, jewel-tipped hairs crowding onto the pale yellow stalks of the anthers, cascading down onto the red centers of the petals, and scattering outward like glass beads spilled on a silk cloth.

Flowers in the genus Lysimachia, like this fringed loosestrife, have gland-tipped hairs that exude oil instead of nectar as a resource for specialized bees. Photo by Emily Stone.

The sparkling droplets weren’t diamonds, of course, but to one local species of bee, they were even more valuable—as their only options for baby food and Tyvek.

Female bees in the genus Macropis collect oil from flowers in the genus Lysimachia, lured in by a special scent that no other pollinators can detect. The bees spread that oil on the walls of their nests, where it keeps the tiny soil tunnels dry in the summer and humid in the winter. They also mix the oil with pollen to make bee bread as food for their babies. Many of our solitary, native bees who nest in the ground need to line their tunnels with waterproofing, but they secrete wax and oil from their own bodies to do the job. And they mix nectar with the pollen to make bee bread.

Just one species of oil bee lives in Wisconsin (Macropis nuda). Their days begin mid-morning, as the males wake up in the cozy embrace of a buttercup or other nearby flower. Females sleep in their shallow ground nest, and seem to rouse a little deeper into the warmth of day. Both males and females perch on leaves to bask in the sun and venture out to non-loosestrife flowers to drink nectar for their own energy. By noon, females begin to visit loosestrife flowers that are receiving full sun, and males—with black bodies and yellow foreheads—patrol nearby in search of mates.

When a male wants to mate, he skips all formalities and simply pounces on a female. If she is receptive, they tumble together for a second or two, and then fly off separately. If she objects, the female bee kicks out her hind legs and dislodges him. She may then continue to forage with her hind legs held high as a reminder of her rejection. This gesture is even more effective because the female bee’s hind legs are lushly furred with white hairs that contrast with her black body.

Macropis nuda female. Photo by

The Packer Lab - Bee Tribes of the World.

 

The fur serves another purpose, too. Short, finely dissected hairs hold oils like a sponge and stiffer hairs support the sodden mat. Using hairy pads on their front legs, females scrape oil from the flower onto her hind legs. She can also collects oil and pollen simultaneously, and carry them mixed together in a ball.

The mother bee places this bee bread inside a small nest cell that she dug into soil and lined with oil. She lays a single egg and closes the cell. The larva hatches, feeds for 10-14 days, and spins a cocoon that completely fills the cell. The cocoon is so waxy and waterproof that the larva must leave a small hole for gas exchange as they breathe through the winter. An adult bee emerges the following spring.

This story has been playing on repeat for roughly 100 million years. The oldest known fossil of a bee is in the same family as our Macropis nuda. That means they flew with dinosaurs, just as flowering plants evolved. A long history doesn’t guarantee a stable future, though. Just like the more visible monarch butterflies, these rare bees are vulnerable to the whims of habitat destruction by humans and climate.

Because I tend to bike past before and after the sun shines on the flowers, I still haven’t seen a little black bee with lushly furred legs visiting my patch of loosestrife. But I like knowing—or at least hoping—that they’re out there...my neighbors in the natural world.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Dragonflies and Emergence

I bent down, then knelt down, then finally sat down on the sun-warmed grass so that I would be eye-level with the dragonfly. Usually they dart off so quickly that I don’t get a good look, but this female calico pennant clung to the tip of a milkweed leaf even as she was buffeted by an afternoon breeze.

Her enormous eyes were the color of sweet cherries, and light glinted off their curve in just the same way. Golden triangles marched down her ebony abdomen. Dark patches on her hind wings, laced with yellow veins, glowed like stained glass in the sunlight. Truly, she was a work of art.

Dragonflies like this female calico pennant are beautiful. They also go through an elaborate process of metamorphosis that is worth pondering more deeply. Photo by Emily Stone.

As I sat mesmerized by the dragonfly’s delicate beauty, thoughts of my to-do list melted away. Instead, a memory surfaced from an essay written by one of my students last semester when I was adjunct teaching. “Whenever I feel distance from myself or want to give up,” she wrote, “the most beautiful creature appears.” Anahi, a student at Northland College whose parents are from Mexico, had been writing about a frustrating time in her life, and how encounters in nature have a way of easing sadness and stress.

Those thoughts resonated with me, but one of her next sentences stopped me short: “We praise dragonflies for their attractiveness, but we never consider the challenges they face for us to see them.”

I saw the truth in her statement immediately. While an adult dragonfly might dart and shimmer for a few weeks of the summer, it can take years for them to get to that point.

“A dragonfly has four stages in their life cycle,” wrote Anahi. “They lay their eggs, form into larva, transition into a molt, and then become an adult. Seems simple, right? Well, that's where we're wrong.” When I first read Anahi’s essay, this sentence felt simple, too. But later, when she told me how young she was when she began translating letters from lawyers, hospital bills, and work instructions for her parents, who were still learning English, I realized that this sentence held a deep wistfulness for dragonflies’ long childhood.

Once dragonfly nymphs hatch from eggs, they may spend anywhere from six months to six years in this youthful stage, before they emerge to become flighted adults. Like tiny dinosaurs, the nymphs roam the bottom of streams, lakes, and ponds, hunting with hydraulically powered jaws for mosquito larvae, minnows, and snails. But even as fierce predators, they risk being eaten by fish and frogs, and being fed to baby loons.

Anahi, too, faced challenges. She watched I.C.E. agents arrive to take away her father. She endured racial slurs, stereotypes, and unkind words and looks. She traveled to Mexico alone to connect with cousins, while her parents remained at home and tried to share the experience vicariously. And, she navigated the college selection and application process largely alone, as the first person in her family to attend college.

Now in Ashland, she often seeks out a bench down by Lake Superior, where she can watch dragonflies and escape for a few minutes from the pressures of her life. She wrote, “Dragonflies have survived for 300 million years because they have strategies to adapt into new environments.”

As a biology major, manager for the lacrosse team, and center of a close-knit group of friends she treats like family, Anahi has metamorphosed into an active young adult. Soon she’ll graduate and spread her wings. Which is why, I think, when she wrote a research paper about dragonflies for her entomology class, she saw the similarities, and the metaphors, in their life cycle.

After having read a semester’s worth of heart-felt essays filled with emotion and wisdom, and having sat across from this soft-spoken young woman while she told me about a life both like and unlike my own, I see the world a little differently. And I read her essay a little differently, too.

“Before they're transformed during last molt in the nymph stage, the dragonfly walks to dry land and sits near the edge of the water,” wrote Anahi. “Once they find a secure spot, away from predators, the thorax begins to slip. The dragonfly begins to ease itself out the nymph exoskeleton. During this step, they also must wait for their legs to gather strength. While they are waiting, the legs and the abdomen start to expand. That process is called emergence.”

“Even if the legs start to gain some strength, they must be careful because they can get tired while waiting, since developing takes time. They end up feeding close to the water or on anything that is close by. Once they are ready, they slowly start moving and flying farther and farther away.”

The calico pennant that had captured my attention finally darted to a perch on the far side of the garden. “Beautiful,” I thought, and also so much more.

Author's Note: This Natural Connections was written in partnership and with approval from Anahi Gill.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

The Myths and Mysteries of Sphagnum moss

Cool water welled up around my ankles, and my feet reveled in the soft, woven texture of the bog mat as I set my muck boots next to a hummock of leatherleaf. As a kid in Iowa, I loved squishing my toes in silky mud. Now I prefer the clean, spongy mosses of a northern bog. I gave everyone along on the “Field Trip to a Poor Fen” the option to go barefoot, but most kept their boots on. They’d already had enough of an adventure just crossing the moat on a fallen log!

The Namekagon Fen State Natural Area is a true gem of beauty and diversity. I’m sure it’s no coincidence that it’s also difficult to access. Over the thousands of years since the glaciers melted away, the basin where the fen sits has been filling with vegetation. Initially, the wiry stems of leatherleaf, an evergreen shrub, would have reached out in a tangle from the sandy shoreline. Those plants formed a sort of scaffolding, and mosses, grown from spores blown in on the wind from refugia where they’d survived glaciation, soon grew thickly, too.

As moss threatened to bury it, the leatherleaf grew taller and reached wider. Dead plants built up, and more species arrived on the wind or the feet of ducks. Eventually the basin filled in, with peat (poorly decomposed plants) forming a thick-but-floating mat across the surface of the pond. Along the edges, with the influence of warm rainwater trickling in, the vegetation decomposed, leaving an 18-foot-wide moat of open water between upland and mat. That’s what we crossed on the log.

I could barely contain my excitement once the group gathered next to one of 7 large pools of open water that dot the mat. The open water indicates the presence of springs, and that groundwater influence is what makes this peatland wetland a fen instead of a bog. A true bog only gets water from rain and snow.

Both fens and bogs are filled with fascinating plants.

Pitcher plants, for instance, have dealt with the lack of nutrients in bogs by becoming carnivorous. They trap insects in their water-holding leaf, and then a large community of small aquatic creatures breaks down the meal, each taking their share of the spoils before the plant itself absorbs nitrogen and phosphorus straight out of the water. (You can read more about this and other carnivorous plants in my archived columns here on my blog. Just type "fen" into the search box.) (You can also watch a video of one of the critters in a pitcher plant eating an ant here.)

Bog laurel, bog rosemary, and black spruce, on the other hand, conserve nutrients by holding onto their tough, narrow leaves for more than one year.

And then there’s Sphagnum moss, the plant that makes those adaptations necessary.

Sphagnum moss grows quickly, and is overtaking this pitcher plant leaf!

Sphagnum is a keystone species—one that has an outsized influence on its habitat. First it clambers out onto the leatherleaf scaffolding, and then it starts sending hydrogen ions into the water. These positively charged atoms (H+) displace positively charged nutrients (potassium K+, and calcium Ca2+) so that the moss can claim them for its own growth. This also increases the acidity of the water. Did you know that pH stands for the “power of hydrogen”?

The dead cells of Sphagnum  moss, which make up all but the uppermost leaves of the plant, also hold water like a sponge. The wet, acidic environment that Sphagnum  creates slows down decomposition in bogs, and the lack of recycling leads to a lack of nutrients available for new growth, partly because few bacteria can be active in such a habitat.

The tops of these Sphagnum mosses were did photosynthesis when alive, while the stems have been dead for a while, and their purpose is to have empty cells that hold water and bacteria. 

As a young naturalist, I was taught that Sphagnum  was used for diapers and wound dressings because of its absorbency, and because its acidity made it sterile. Science has proved that only the first fact is true. With the new DNA sequencing techniques available to scientists, we now know that the hollow cells of Sphagnum  moss are host to a thriving and unique community of microorganisms—bacteria mostly—who carry out a suite of essential functions.

Some bacteria get carbon from methane in the water and thus provide the moss with 20% of its carbon needs. Other bacteria grab nitrogen out of the air, and share it with their host. Many, if not most, of these bacteria are still virtually unknown and poorly understood. Plus, each of the 380 species of Sphagnum around the globe likely hosts its own distinctive microbial community.

It’s obvious to anyone who manages to cross the moat that the Namekagon Fen is a gem of beauty and diversity. Hot pink orchids glittered among lawns of pod grass and beak rush. Dragonflies and damselflies in a rainbow of colors darted among the plants, too. It’s now strange to know, though, that some of the greatest diversity is probably in the sun-warmed, rain-soaked moss that squished up between my very happy toes.

Calopogon orchid

Rose Pogonia orchid

pitcher plant flower

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.