Autumn Apples

Golden sunshine and a bluebird sky arched above as we meandered down a lonely backroad. I was paying attention to driving, but my passenger was focused on something else. “Apples!” he exclaimed suddenly, as we cruised past a few trees in the road ditch. He’s always on the lookout for apples. We turned around and pulled off the shoulder, then rummaged around in the car for bags. Soon we were clambering down the bank.

The first tree we came to had small, yellow apples. One bite was all I needed. The tart, dry flesh was impossible to swallow. We moved on to the next tree. Plucking a deep red apple, I discovered that it had a large brown spot on the far side. A tentative bite revealed mushy, sweet innards. “Might be good for sauce,” I mused. Every fruit we picked had a brown bruise, though.

Looking back toward the first tree I noticed a third trunk, its branches so intertwined the others that we hadn’t noticed it at first. The large, yellow-green apples were burnished with red, and they dangled invitingly among deep green leaves. One bite was all I needed. Crisp flesh fairly jumped through my teeth, and a tart zing added interest to the sweetness. Now this was an apple. We quickly filled our bags.

Arriving home, we discovered the driveway full of an entirely different type of apple. Small, brown, dried-out spheres lay among the fallen oak leaves. If you could make ping pong balls out of brown paper bags, this is what you’d get. Not very appetizing, but then that’s not their goal, and their purpose has already been fulfilled.

Oak apples are not a fruit at all. They are galls – the nurseries for tiny wasp larvae. Earlier this summer, a woman pulled a similar gall out of her pocket so I could identify the outbreak at her home. The color drained from her face when I mentioned wasps, and I could see through her panicked expression that she was imagining a swarm of yellow jackets ambushing her yard. Luckily, the wasps that create these galls are the small, non-stinging kind, and she has nothing to worry about.

While oak apples won’t make good applesauce, they do provide food for thought. Oak apple gall wasps (there are several different species) have a complicated, double life cycle, known as the “alternation of generations.”

The brown, papery galls now on my driveway once protected growing and pupating wasp larvae high in the branches of an oak tree. Male and female adult wasps exited the galls this summer. The wasps mated, and then the females burrowed into the ground where they laid their eggs on the roots of oak trees. The larvae from those eggs will feed on the roots of the oaks for more than a year before they pupate. They emerge as generation of female-only, wingless wasps. This underground segment of the life cycle, from egg to larvae to pupa to wingless female adult, takes over a year. The offspring of the galls I found this fall won’t surface until May of 2017.

As the ground warms in spring, the wingless females will emerge and crawl up a nearby oak tree. In this asexual generation there is no need to mate. The females will inject eggs into expanding leaf buds. The small, round, larvae of the next generation include both males and females who chew into the leaf stems. Chemicals in their saliva stimulate the leaf tissue to swell. The galls continue to expand as the leaves and larvae grow, providing both food and shelter to the developing wasp.

These larvae pupate in late summer, and emerge as small, dark, male and female wasps to begin the cycle again. Once empty, the galls drop to the ground and dry out.

Just like the true apples we picked along the road, galls come in a diversity of colors and textures. There are over 50 species of wasps that produce oak apple galls in North America, and each wasp’s gall is slightly different. Most fall into two general groups – galls that have an airy web of fibers radiating from the central larval capsule, and galls that have juicy, spongy, fruit-like tissue. All galls made by Cynipid wasps would taste terrible, though, since they concentrate bitter tannic acid from the oak as a defense against fungi and bacteria.

The tart zing in my apples will also keep bacteria at bay – and taste great – once I preserve them as sauce. Oh autumn, you are the apple of my eye!

Photo by Steven Katovich, USDA Forest Service

Boundary Waters

Walking down to the lake one last time before heading to the tent, I couldn’t resist turning off my headlamp and looking up at the stars one last time, too. Here, in the Boundary Waters Canoe Area Wilderness of northern Minnesota, we are many miles from any significant light pollution. The dry, breezy September day had cleared humidity from the sky, too, resulting in a brilliant celestial show. Even familiar constellations were almost lost in the lavish abundance of light.

As I watched, I began to notice something else obscuring the stars. Just above the tree line, a gauzy haze had materialized. It swept around to the north, and dimmed a swath of the sky. I was puzzling at such a peculiar intrusion of clouds, when suddenly the haze developed two vertical bars. These weren’t clouds—they were northern lights!

Snapping my headlamp back on for expediency, I hurried back up the toe of granite toward our cluster of tents. John was already on his way down. “Northern lights!” I exclaimed as we passed. I shook Brenda and JoAnn’s tent gently, “The northern lights are out!” Ed was still reclining next to a few glowing embers in the fire grate. I could hear my dad rustling around in our tent, and see Jane’s light bobbing in hers. “Northern lights!”

One by one, our crew on the Natural History Paddle in the Boundary Waters picked their way down the campsite’s classic lakeside rock outcrop, and came to sit and stand at the water’s edge. Silently, we watched as the arc of greenish-white light rose and lowered, then split into two layers like a double rainbow. Dim vertical bars came and went almost imperceptibly. There were no wild dances, no flashing colors, just a demure display of physics above a gathering of new friends.

Before scientists discovered that solar winds cause the Aurora, many cultures created beautiful and fascinating stories to explain this mysterious phenomenon. Norse mythology tells of mounted warriors with light reflecting off their armor, and the massive ice of glaciers releasing stored energy. Chinese mythology imagines dragons’ fiery breath flashing across the sky. Others believe in spirits of ancestors dancing overhead, and reflections off ice at the North Pole.

In just the past 50 years, science has told us that the northern lights, or Aurora Borealis, are produced through an interaction between the Sun, the Earth’s magnetic field, and gasses in our atmosphere.

It begins with a coronal mass ejection (CME). The Sun ejects a stream of material, called solar wind. If it is aimed toward Earth, then the solar takes between one and four days to arrive at Earth. Once it arrives, the Earth’s magnetic field channels most of the electrically charged particles in the solar wind safely around the Earth.

Only where the magnetic field dives downward – near the North and South Poles – do the particles get close. Here, 50-200 miles up in our atmosphere, the electrons and other charged particles in the solar wind bump into oxygen and nitrogen molecules. Oxygen and nitrogen have their own electrons, which can gain or lose energy. So, when electrons from a solar wind bump into and transfer energy to oxygen and nitrogen, it boosts their electrons into a higher energy state. These “excited” electrons are unstable.

As an excited electron relaxes back to a more stable energy level, it releases energy in the form of a photon of light.  The size of the energy change determines the color of the light. As we relaxed back into a more stable energy level after the excitement of the day, perhaps we glowed a little bit, too.

Of course, none of us were thinking about the physics of our experience as we stretched our stiff legs and wiggled cold fingers. We were admiring the stars (still reflected in the rippling lake), anticipating the warmth of fluffy sleeping bags, and exhaling gratitude. Watching northern lights from a slab of bedrock in the Boundary Waters, canoes tucked safely into the trees nearby…is there any better way to spend an evening?

“I wondered…if anything—even knowing the physical truth—could ever change the beauty of what I had seen, the sense of unreality.  Indian warriors, exploding atoms, beds of radium--what difference did it make? What counted was the sense of the north they gave me, the fact that they typified the loneliness, the stark beauty of frozen muskegs, lakes, and forests. Those northern lights were part of me and I of them.” 

-- Sigurd Olson

The Aurora-watching rock was great for sunrise fishing, too. Photo by Larry Stone

Isle Royale: How did orchids get here?

“Rattlesnake!” I cried out as I stopped abruptly and shifted my pack so I could look down at the ground. Excitement (not fear) was surely evident in my voice, but not many people would recognize the source of that excitement. No snake, but several whorls of grayish-green leaves with white markings hid within the leaf litter along the Minong Ridge Trail on Isle Royale. The checkboard pattern that adorns the leaves is said to look like a rattlesnake’s mottled camouflage, while the broadly oval leaves are similar in shape to plantain leaves (a common plant of yards and disturbed areas). Together, these features resulted in the name “rattlesnake plantain orchid” for this beautiful little plant.

Throughout my hike on Isle Royale, I continued to see clusters of the three different species of rattlesnake plantain orchid along the trail, as well as several other less distinctive orchids, already past flowering. The family Orchidaceae is one of the two most diverse plant families (Asteraceae is the other), and contains more than 22,000 species across the globe. The flowers range from extravagantly beautiful to dinky and unobtrusive. Many orchids have evolved highly specialized pollination systems. Some look just like female bees, and attract amorous male bees to do their cross-pollinating. Many have special landing pads on their petals, and distinctive scents wafting out to entice visitors.

What fascinates me the most, though, is what happens after an orchid is pollinated. The seeds that form are almost microscopic, and over a million of them can fit into the capsule that develops from a single flower. Being so tiny, they lack an endosperm. This little packet of starches, oils, and proteins usually gives seeds the energy they need to germinate, grow their first leaves and roots, and get along until they can sustain themselves. Corn, beans, and squash are great examples of seeds with large energy reserves, and their seeds sustain us, too.

Orchids have found another way.

In order for a dust-like orchid seed to germinate, it must first be infected by a specific fungus. Not all orchids form a symbiosis (a close living relationship between two species, whether or not they both benefit) with the same fungus, but each orchid has just one fungal species, or maybe a few, that will work for it. The fungal mycelia provide the seed with sugar and nutrients in place of the endosperm. It is unclear if the fungus receives anything in return. The seeds can’t germinate without their fungus, except in lab conditions with a source of sugar. Once colonized, a baby orchid plant, called a protocorm, grows, and eventually produces leaves and roots. Some orchids never produce leaves or chlorophyll at all, and live out their days entirely parasitic on a fungus.

Knowing these basics of orchid germination, the question I’d been asking everyone and everything on the island baffled me even more: “How did you get here!?” How could these tiny, fragile seeds make such a long and treacherous journey, 14 to 20 miles across the lake, and then just happen to land where their friendly fungal partner was already established?

My amazement only deepened when I used the latrine near our Rock Harbor campsite for the first time. The educational poster on the inside of the door bragged that Isle Royale is home to 32 species of orchids. Thirty-two times--at least--over just several thousand years, this amazing coincidence happened. Wow.

When I shared my amazement with a mycologist friend, though, he was less impressed. “It’s almost inevitable,” he shrugged. As it turns out, the numerous, minuscule seeds of orchids are well-adapted to wind dispersal – in much the same way that pine pollen drifts on the breeze. That’s how orchids colonize tree trunks in the rainforest. Likewise, fungal spores are often wind-dispersed, even over many miles, and the species of fungi that orchids parasitize are quite common.

A little more research revealed that Ontario –the province just upwind of Isle Royale – has over 50 species of orchids on its mainland. So maybe 32 species on Isle Royale isn’t that impressive after all.

With this new information, my amazement at the simple fact of orchids being on Isle Royale shifted to admiration for the adaptations that brought them to the island in the first place, and the intricacies of their symbiotic relationships. Perhaps my question “How did you get here?” should refer not to the island, but to this moment in time, and the state of exquisite adaptation housed in a ground-hugging, snake-skin patterned cluster of grayish-green leaves.

How quietly, and not with any assignment from us, or even a small hint of understanding, everything that needs to be done is done. – Mary Oliver, Luna

Named for their supposed resemblance to the pattern on a rattlesnake’s skin, rattlesnake plantain orchids are a delight to encounter on the trail. How did they get here? Through millennia of adaptation.Photo by Emily Stone. 

Isle Royale: How did you get here?

We heaved our backpacks, loaded with high-energy foods, waterproof tents and warm clothing, onto the ferry dock just as the gray dawn was beginning to break. Waves crashed around the Voyageur II, and gusts of damp wind threatened to steal our hats. The ferry captain came out to greet us, passenger list in hand. We collectively expected him to say something like “All aboard!” Instead, with a bemused smile, he projected his voice over the bluster to the waiting crowd and said “We’re not going.”

At first there was just stunned silence, with a few hesitant chuckles, since he looked like he might appreciate a good joke. But he wasn’t joking, and neither was Lake Superior. Eight-foot waves and 30 mph gusts across a 20 mile expanse of cold, open water are nothing to mess with. “This is your one chance for a refund,” he said, “otherwise be here by 4:45 a.m. tomorrow.”

So, for plan B we headed up to the Grand Portage National Monument Visitor Center. The park ranger at the front desk didn’t miss a beat when we told him of our delayed departure to Isle Royale. “Welcome to a long tradition of people waiting at Grand Portage for good enough weather to start a journey on Lake Superior.”

The voyageurs who rendezvoused here every summer through the height of the fur trade era called Lake Superior “The Lady.” And this Lady makes her own rules. Icy water, big winds, and craggy rocks don’t make for safe or easy travel. Gardens of shipwrecks can attest to that. But rising out of the crystal clear water, 14 to 20 miles from shore, is a bit of an anomaly. Isle Royale, a 45 mile long and 9 mile wide bedrock island, is teeming with life that somehow made the treacherous journey.

The next morning, with the rough, rolling, cold, wet ferry ride behind us, we disembarked gratefully at the Windigo dock on the southwest corner of the island, joining the many lives already there. After cooking oatmeal in the campground, we hoisted our packs and started off down the trail.

Before long we met several pairs of hikers just ending their trips. We asked about their route on the island, their hometown, and which ferry they took. In essence, we asked “How did you get here?” Mostly they used the water route, but one couple arrived by air in a float plane. Historically, making winter crossings by dogsled was also common. Isle Royale is not an easy place to get to, or to get around, and yet life surrounded us on all sides. Soon I started asking “How did you get here?” to everything we saw.

While relatively few humans arrive on the island by air, many of the island’s wild residents and visitors arrived that way. The haunting wails of loons drifted up from every lake we passed. Chickadees chattered above us as we hiked, while flocks of cedar waxwings played follow-the-leader between berry-laden mountain ash trees. It’s not hard to imagine how the birds got here, or how the seeds of their favorite fruits got here either.

Fruit-bearing shrubs like chokecherry, mountain ash, and serviceberry are often pioneering species, since their seeds are air-dropped in a packet of fertilizer. The vibrant, red fruits of thimbleberry caught our attention, too, and supplemented our quick breakfast. Slowing down to pick berries left us open to attack, though, from the delicate mosquitoes who once made the dangerous crossing, too.

While the whine of mosquitoes was pleasantly rare, red squirrels scolded us incessantly. A water route seems like the only plausible explanation for the squirrels’ presence. Did the first squirrel on the island drift here on a fallen tree or raft of vegetation? What a frightening ride without a motor, rudder, rain gear, warm sweater, or pack full of food! How many attempted journeys failed – with no refund!? Now the red squirrels have been here so long – separated from the mainland population by that arduous journey – that they are considered their own subspecies: Tamiasciurus hudsonicus regalis.

Not just a scolding, but a crashing in the brush caught our attention. Through the dense spruce trunks we caught a glimpse of the hulking silhouette of a cow moose as she vanished into woods.  Moose are thought to have swum here from Canada around 1900 during a time of overpopulation on the mainland. And they didn’t have a bowl of warm oatmeal to greet them at the end. The trees they browse were here already, though, having colonized the island (by air or water?) starting shortly after the glaciers retreated 11,000 years ago.

Having sighted one of the iconic species of Isle Royale, we were now on the lookout for the other: wolves. Large, hairy scat on the trail signaled their presence, as did a few big, four-toed tracks among the boot prints on muddy trails. With only two or three wolves left on the island, that is more sign than I’d dared to hope for. Wolves likely crossed the ice bridge in the winter of 1948-49, and they helped stabilize the moose population for many years. Now wolves are suffering from inbreeding – one liability of living on an island – and the Park Service is exploring management options for both wolves and moose.

Air, water, ice. It is almost easier to imagine how the 1.1 billion year-old bedrock of this island came to be than to imagine how such a diversity of seemingly fragile organisms came to colonize it. Perhaps most telling is that not everything did make it. Bears, raccoons, skunks, porcupines, cottontails, and snapping turtles are notably absent. For humans, too, Isle Royale National Park is one of the least-visited parks in the country, and one of the most costly to visit (measured in time, money, and the discomfort of seasickness). Perhaps I’m biased, but I think that makes the creatures who do get there a little more special.

The cold, clear waters of Lake Superior separate Isle Royale and all its life from their counterparts on the mainland. The Lake makes the Island.

Red squirrels are one of the few small mammals that were able to make the treacherous crossing on Lake Superior and get to Isle Royale. By their incessant scolding, you’d think that they now own the place! Photo by Larry Stone.

The Corn Belt Tightens the Belt on Monarchs

One of my most vivid childhood memories from Iowa’s corn country is watching clouds of monarch butterflies dance around the milkweed patch by our back steps and finding caterpillars on the leaves. My brother and I raised them, as many kids do. They were the first butterfly I learned to identify, and just knowing their name made them more special.

Even as an adult, I watch eagerly for monarchs all summer. On a recent hike with local naturalist and author John Bates, he philosophized that “monarchs might be the next passenger pigeon.”  Indeed, their population has been in decline since 1997 (from a high of about a billion individuals, down to just 35 million) and a recent study warns that there is a greater than 5% chance that they will experience “quasi- extinction” (less than 1000 individuals) within a century.

In the past, it was easy to blame our southern neighbor for the declines. Illegal logging with mafia-like techniques in the mountainous butterfly preserves of Mexico was a major problem, but it has largely been addressed by the Mexican government. There is still more to be done with supporting the local economy so that the locals won’t need to extract resources from the protected forests, but the biggest challenge to the monarch’s struggle for survival is no longer across an international border. It is right here in the US, in the every-more-productive Corn Belt where I grew up.

The incredible migration that monarchs are beginning just now will culminate next spring in a flurry of reproduction. The butterflies that fly south from Wisconsin and Minnesota this September will overwinter in the remote oyamel fir tree forests in the mountains west of Mexico City. In early spring, those same monarchs will head north again – hoping to lay their eggs on spring-fresh milkweed plants in Texas before they breathe their last butterfly breath.

But what if there isn’t any milkweed? Drought, cold weather, and habitat loss have all been recent issues. And the challenges continue as generations of monarchs leap-frog north into the Midwest – into the infamous Corn Belt. A majority of monarch butterflies on the Mexican wintering sites are born in the Corn Belt. Since the first genetically modified (GMO), herbicide resistant soybeans were introduced in 1997 (with GMO corn following shortly), there has been an 80% decline in milkweed in the Midwest, and a concurrent 81% decline in monarchs. In Iowa, one biologist estimates there has been a 98% reduction in milkweed on the landscape.

 “What we’re seeing here in the United States is a very precipitous decline of monarchs that’s coincident with the adoption of [herbicide-resistant] corn and soybeans,” says Chip Taylor, founder of Monarch Watch.

While GMO products have garnered support among some scientists for their apparent food safety, the changes that GMOs have caused in our farming practices and the subsequent habitat loss for many organisms (not just monarchs) are a significant bit of collateral damage. More GMO crops – some resistant to several types of herbicides—are in the development pipeline.

It’s not just GMOs and glyphosate herbicides. Farming practices have changed a lot since my Grandpa Warren hunted pheasants among fencerows in central Iowa. With corn prices soaring, bigger equipment, and bigger farms taking the lead, and subsidies for ethanol taking the place of the Conservation Reserve Program (CRP) subsidies, more of the land is under cultivation than ever before.

“Overall, genetically modified, herbicide-resistant crops have increased the current, and predicted future, extinction probability of monarch butterflies in eastern North America,” agree a team of international scientists writing for the Journal of Animal Ecology last year. They found that, while winter mortality is still an issue to contend with, the loss of milkweed in the Corn Belt is the greatest factor precipitating monarchs’ population declines. That same article admonishes that addressing these challenges is “the highest conservation priority.”

There is some good news. Favorable weather and efforts by back-yard conservationists like Eve Depew and Cec Peterson have helped. Chip Taylor just wrote in his most recent Monarch Population Status blog post at MonarchWatch.org, that “The number of eggs found …now leads me to suspect that the migration through the upper Midwest will be better than any migration seen since 2011.” A year of population growth will be very welcome.

Habitat loss is the biggest problem, and you can help. Every extra back-yard milkweed plant and un-sprayed flower garden could host one more caterpillar, and provide nectar for hundreds of pollinators. Getting the Department of Transportation, the Forest Service, and the National Park Service involved can offer access to even more acres.

But gardens like these “are not going to make up for 25.5 million acres of additional corn and soybeans,” says Chip. Large conservation efforts – and sustainable farming practices – also are necessary. You can help there, too, by choosing carefully at the grocery store, by supporting the organizations doing good work, and by letting your representatives at all levels of government know that you value conservation efforts. Several concerned groups banded together last year to ask that the monarch butterfly be listed as “threatened” under the Endangered Species Act, which would increase funding and research into their recovery.

Should we do all of that work, and make all of those sacrifices just to save a single species of beautiful, amazing butterfly? No! We should work to save the monarch because in doing so we will also be saving ourselves, our planet, and the futures of kids like Eve.

Monarchs are experiencing steep population declines, mostly due to farming practices in the Corn Belt. Why should we care? For the futures of kids like this one! (Who just happens to be my nephew Derek, from the heart of corn country in central Iowa.) Photo by Larry Stone. 

Monarch Migration Miracles and Challenges

“Absolutely spectacular. Nothing compares with it.” Effused Cecilia Peterson as she sat down to tell me about her three visits to the monarch butterfly overwintering sites in Mexico. At first glance, Cec (pronounced “cease”) – a retired elementary teacher and avid gardener – doesn’t have much in common with Eve Depew, a seven-year-old girl raising monarchs in Hayward, WI. But as Cec continued, describing the amazing experience of being in a forest with butterflies practically dripping from every trunk and branch, the enthusiasm and wonder that lit up her weathered face was exactly the same as Eve’s. They have yet to meet, but these girls are like two peas in a pod.

In fact, Cec can more than empathize with Eve’s efforts. Starting in the mid-1990s, all the fifth graders in Cec’s inner-city Duluth, MN, classroom raised a monarch from egg to adult in a plastic shoebox on their desk. “That experience with nature overrode any behavior problems,” reminisced Cec.

In the beginning, students like Cec’s would have only learned about the mystery of where monarchs go in the winter. While the overwintering sites have been known to locals for many years, science only discovered them in 1975.

Since then, the students all over the country have learned about the amazing migration that monarch’s undergo, and the remote oyamel fir tree forests in the mountains west of Mexico City where they rest from December to April. On steep, southwest-facing slopes, ten-thousand feet above sea level, the temperatures are just right. There, in the cool, moist microclimate in the trees, monarchs bide their time. The forest is both their umbrella and their blanket. The dampness helps keep them from dehydrating, while the canopy prevents dangerous wetness. Moderate temperatures under the forest cover prevent them from freezing to death, while still being low enough to slow their metabolism, and stretch out their limited fat reserves as long as possible. On warm days, they will fly nearby for a nectar snack and drink of water.

Dangers still abound in the forest, though. The canopy can’t totally eliminate freezing temperatures or ice storms, and especially when a cold snap follows rain, wet butterflies may freeze. One such storm happened the year that Cec returned to the forest for her second visit. Instead of ethereal beauty, she remembers the horrendous stench of rotting butterflies. As our climate changes and extreme weather becomes more common, scientists are worried that those dangerous storms and temperature fluctuations will happen more frequently.

Compounding the weather issues are pressures on the forests to provide useful products for local residents. Although the wintering areas have been set aside as Biosphere Reserves, monitoring shows illegal logging is taking its toll. “At night, in my hotel, I could hear HUGE logging trucks rumbling down the mountain from the butterfly groves,” lamented Cec. Because of that, many of the monarch conservation efforts have been aimed at protecting these winter refuges. While the large-scale illegal logging practices have largely been brought under control since Cec last visited, the thinned forests and continued subsistence harvest of the trees allows more moisture to get through to the butterflies, and they retain less heat.

Some natural predation occurs in the mountains as well, since a couple types of birds and one species of mouse have adapted to eating the sleepy butterflies. This is no mean feat, since the toxins that caterpillars acquire from milkweed plants survive metamorphosis and remain in the adults. The critters have adapted, though. One mouse can eat about thirty-seven monarchs a night in the oyamel forest.

With almost all of the continent’s monarchs concentrated in one region (another smaller population overwinters in California), they become vulnerable to a single storm, drought, fire, disease, or human transgression.

The concentration of monarchs also brings in a high volume of ecotourists, who mean well, and who can help support the local economy, but who can sometimes impact (literally, with their feet) the very beauty they came to revere.

Despite all this, many monarchs survive the winter. The warmth of spring triggers a mating frenzy, which also triggers their reproductive diapause to end. Females can mate before they are sexually mature, and both mating and the presence of milkweed seem to speed up their development.

In mid-March, these long-lived butterflies begin the last leg of their journey. Their destination is fresh, spring milkweed in the southern United States. Here, at the tail end of their 3,000-mile, 8-month journey, comes the most significant challenge they’ll face. Seven-year-old Eve knows about it. Cec gardens because of it. And there are things that you can do to help. More about that next week.

Overwintering monarch butterflies in a preserve outside of Angangueo, Mexico, completely cover some trees. Photo from Wikipedia. 

Monarch Migration Begins

I see them everywhere now. Deep orange with black trim, monarch butterflies dance among the wildflowers we planted for them. Two, then three, then four! Are they fighting or loving as they bang their delicate wings? Then, calm for an instant, they alight on the many-petaled clusters of butterflyweed and sip its abundant nectar.

I look closely while they are still. One, at least, is a male. I can see the slender black lines with a swollen black dot on each of his hindwings as he unfurls his slim proboscis and drinks deeply through its hollow center. This amazing tube is made of two long, C-shaped channels, which the butterfly joined together with tiny hooks and fringes after he emerged from his chrysalis. Even now, if his proboscis gets clogged with sticky nectar, he can unhook the two channels to clean them.

As a female – with robust black lines – explores a nearby butterflyweed, I try to watch her feet. Butterflies taste through their “toes,” identifying their platform as a milkweed, and also determining its quality as baby food. While this low, bushy plant looks nothing like common milkweed, it is a close cousin, and one of the few host plants that can nourish monarch caterpillars. Each female lays an average of 700 pinhead-sized eggs during her two-to-six-week lifespan.

Leaning in closer—hoping to catch her in the act of egg laying—I startled her into flight instead. Monarchs, with their compound eyes, have almost 360 degree vision, and use it to detect predators even with their head in a flower.

The eggs that are laid now, in mid-August, will become butterflies who live longer and fly farther than their parents. The eggs laid now will become the migratory generation, and take part in an amazing, two-month-long journey. Monarchs produce three to four generations per summer, and the population grows with each new generation. By early fall, monarch numbers are at their peak.

The shortening days and cooler nights of fall trigger many seasonal changes in the northwoods. Leaves begin to show their brilliant fall colors, birds stop singing and begin to migrate. Many insects enter an overwintering phase of their life cycle. Monarchs are no different. The onset of fall triggers the larvae and pupae of monarchs to enter "reproductive diapause." They metamorphose into pre-pubescent butterflies who cannot yet reproduce, but who are ready to journey south.

This happens all across the monarch’s habitat at slightly different times. Canadian butterflies begin their migration earlier, swirling through Wisconsin at about the same time that our butterflies are ready to head south, too. Eve Depew, the seven-year-old scientist from Hayward, WI, who has been raising monarchs all summer, has more than a dozen chrysalids that are close to emerging. She will name and photograph each monarch, then send them out to start their journey.

The building wave of peak monarch abundance hits us here in early September. The surge reaches Houston, Texas, in mid-October, and the butterflies’ destination – the Transvolcanic Mountains of central Mexico – in mid-November.

These young butterflies have never seen their destination–nor did their parents, grandparents, or even great-grandparents. Flying only by day, they navigate with some combination of sunlight (the ability to see polarized light lets them know the position of the sun, even when hidden by clouds), and magnetism. Tiny “Johnston’s organs” at the base of each antenna are sensitive to stretching. They are used to detect wind and gravity, and maintain balance and orientation during flight. They may also be able to detect the Earth’s magnetic field.

Even with such sensitive instruments, it is a mystery how these tiny (and thus tiny-brained) butterflies even know where they are supposed to end up.

Watch for the change in monarch flight patterns as fall approaches. Their erratic fluttering from flower to flower is replaced by directional flight. Heading south, they rise on thermals of warm air, and soar on wind currents just like birds. Like a hot-air balloon pilot, they fly at the altitude with the best wind direction. And they avoid flying on days with a strong headwind. Scientists using a model butterfly have discovered that the forces from tiny eddies of air created during each wing flap generate lift. By using all of those efficiencies and by feeding regularly, monarchs are actually able to gain weight on their two-month-long trip, and can travel at least 265 miles in a day!

Entering the winter with plenty of fat stored in their abdomens, millions of monarchs prepare for a long wait. This migratory generation must face a host of perils not encountered by their parents. And the continuation of the species rests on their tiny shoulders. (More about this next week.)

Do you have monarch eggs, caterpillars, or butterflies in your yard, too? We may be in the presence of the greatest generation.

Monarchs that are born at the end of the summer don’t fully mature. Instead, they enter “reproductive diapause,” and live longer than any other generation – long enough to fly to Mexico for the winter. The thicker black lines on the butterfly mark her as a female. Photo by Larry Stone.