An early spring blessing

"See the little cutworm,
brave and cunning soul." -Anon.

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I

If you were to cross the Mississippi River from Iowa to Wisconsin on the Lansing bridge, and then head north along the highway that follows the river at the base of the bluffs, you'd soon come upon an imposing feature with a stark and soulful presence.  It is a wild, windswept slope of grass and rock, looming obscenely out of the bluffside -- the mighty chest of the embodied Earth, bared for all to see.

View of Battle Bluff Prairie from Hwy 35, north of De Soto, WI

This prairie is defined by extremes.  It is so steep that in places one must crawl upward on all fours.  Outcrops of rough black stone jut here and there from the slick, wiry native grasses, and sharp-edged rocks shift suddenly underfoot.  The south- and west-facing slope bears the full force of our powerful Sun, which sears off recently fallen snow even while the nearby roadsides and floodplains are covered in thick frozen blankets of white.  During the growing season, there is little shelter from the pounding heat and harsh brightness.  Eagles and turkey vultures wheel overhead, and chiggers scuttle up the legs of careless visitors.  On a few fateful days in the 19th century, this prairie bore witness to the brutal end of the "Black Hawk War," in which U.S. Army troops and their allies cornered and slaughtered a band of First Nations people attempting to flee across the river.  For this unconscionable distinction, the grassy landmark earned its present-day nickname: Battle Bluff.

Amid all the harshness, Battle Bluff Prairie possesses a beauty that is by turns austere, hopeful, and even riotous.  Once, I clambered up the slope in the slaty blue-gray cloak of predawn, on one of those September mornings in which all the moisture had fallen out of the cold clear sky the night before and now rose up again in a thick, drenching, low fog.  Every leaf and blade of grass drooped, sopping wet with dew.  I stood on the slope quietly as light began to suffuse the river valley.  At first, immersed in pea soup, I could see only a few feet around me.  Even as the sun rose, attempting to pierce the layers of gray, the horizon and all below me was obscured.  I savored what illumination there was.

Before long the air around me began to clear.  A glinting orb-web caught my eye.

Eventually, the full light of day revealed a rare and precious remnant prairie, resplendent in late-season wildflowers and the delicate russet hues of dried-down grasses.

The river valley stretched to the south.

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Months later, after winter's longest and coldest days had passed, I returned to Battle Bluff on a mild and sunny day in mid-March -- three years ago today.  Though treacherous to navigate as usual, the slope was warm and dry.

The wildflowers, grasses, and other plants I'd enjoyed the previous fall had long since drawn their energies into the ground for the dormant season, leaving behind seedheads, leaves, and culms in various shades of tan, brown, and gold.  But clear skies and above-freezing temperatures in recent days had made me wonder if some hardy breed of plant life might have awakened in a sun-soaked place like Battle Bluff.  Indeed, as I moved gingerly across the prairie, I was delighted to find, sprouting out of the thin soils, a pale little gray-green plant covered densely in white hairs.

Clearly, this was a unique creature -- eager, adaptable, and tough.  (Its name?  Wormwood, Artemisia campestris var caudata.)  Though the rest of my time there that day produced few other early signs of spring, my spirits were lifted.  As I left the prairie, the waning sunlight conjured an ethereal mood.

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A week later I was back, and the wormwood was continuing its slow but steady March toward spring.  Crouching to admire one wormwood sprout, I noticed an elongate little something attached to one of its leaf-tips.  The color pattern of the miniature mystery object had caught my eye -- a repeating pattern of light brown chevrons, like a dead needle from a cedar tree.

I was surprised to discover that this was a tiny caterpillar with its head buried in a hole it had mined in the leaf-tip.  Here's the leaf tip with the hole in it…

…and here's the leaf-miner.  (The "chevrons" aren't quite as obvious in this lighting.)

Though I didn't bring this caterpillar home with me to rear, I did post pictures of it to Bugguide.net, a citizen science website used by thousands of insect enthusiasts all over the United States and Canada.  Nobody there recognized it, but those who responded to my post encouraged me to investigate this animal further.

It was almost two years before I found the time to do so.

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II

In late February and early March of 2017, I revisited Battle Bluff several times.  Now, though, I brought with me a research permit from the Wisconsin DNR and a particular goal: to find and collect live specimens of the mystery caterpillar, which I would attempt to rear to adulthood.  Here's what the prairie looked like on Feb. 21:

My notes from that day read, in part: "Found two of the Artemisia larvae…. The first was curled around a leaf tip.  The second I found by parting the leaves in the center of the shoot / crown.  Only 1-2" of growth on the Artemisia."  I took home one of the two larvae (along with some wormwood leaves to feed it) and photographed it that night on my kitchen table.  As you can see, it's pretty darn mini.

Three days later, it had grown, but not by much.

During my March 5 visit I collected four more caterpillars and a fresh bunch of wormwood leaves.  I harvested only one or two leaves from each plant, since the wormwood (like the caterpillars) was still pretty small:

As I located and captured the mystery caterpillars, I noticed a peculiar habit of theirs.  When I came upon a larva in the field, and moved in close to observe it -- often accidentally jostling part of its host plant in the process -- the larva would drop suddenly from its leaf-perch, wriggling its body back and forth.  The wriggling action tended to work it rather quickly into the leaf litter and debris beneath the plant, where it blended in masterfully.

I don't remember quite how the idea came to be, but a few days later my friend Brad and I hatched a plan to gather footage of this interesting evasive maneuver, using his tripod-mounted video camera.  On a March 19 visit to Battle Bluff, Brad recorded a larva's "wriggle move" on camera -- along with other footage of a larva crawling over its hostplant and feeding.  During that outing we also collected two larvae for my rearing project, bringing my total number of captive caterpillars to seven.

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III

By late March, the "tiny brown chevron larvae" in my rearing containers were starting to get big, fat, and muscular.  (Look what a vegetarian diet can do!)  Here's one I photographed on March 26.

On April 23, one of the caterpillars pupated -- and by May 9, the other six had pupated, too.  That all seven of them survived to pupation seemed unbelievably fortuitous.

Of course, once I was done waiting for my charges to pupate, it was time to wait again -- for adults to emerge.  I carefully regulated the moisture in their containers.  I drummed my fingers.  I checked up on the pupae compulsively -- sometimes several times in a day.  I had poured so much grunt work, attention, and love into these creatures, and I desperately wanted them to make it to adulthood.  Even just one or two of them -- please.

On May 30, my wish was granted.

Welcome to the world, lovely scale-wing!

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In the following weeks, more adults emerged; the rearing was a success.  I knew I'd need to "retain" (kill and preserve) one or more of the adults and send the specimens to an expert in order to obtain a clear-cut species-level identification.  But the way things were going -- with the animals surviving so well -- it seemed likely I could end up with seven adults, and I certainly didn't need to keep that many for the sake of science.

 So it was that I made a final trip to Battle Bluff in early summer to release three pupae and an adult.  The killing-and-preserving part of insect work is usually tough for me to do -- I get attached -- so I was grateful to be able to return some of the wormwood moths alive and unharmed to their prairie home.  It felt like the right thing to do.

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IV

"This represents a pretty significant finding of larval behaviour," wrote Chris Schmidt.  Note the "u" in "behaviour" -- Dr. Schmidt wasn't writing from the United States.  He works as a research scientist for the Canadian National Collection of Insects, Arachnids & Nematodes.  (How cool would it be if our country had a government institution with "Insect" in its name...let alone "Arachnid" or "Nematode"?)  Chris was responding to my request for information about the wormwood moth, which (I had learned) belongs to a group of Lepidoptera in which he specializes.

"There is virtually no info in the literature on this species," Chris explained.  "Lots to learn about these moths...they generally get ignored or overlooked because they are perceived as dull and boring!"  To show me what had been previously known about the wormwood moth -- whose official name is Euxoa immixta¹ -- Chris pointed me to an article published in 1987 (the year I was born, as it happens).  In it, the author, J. Donald Lafontaine, writes, "The immature stages of immixta are unknown.  This is a species of the central and eastern Great Plains and relict prairie habitat to the west of the Appalachian mountains. ... Adults have been collected from late April until early September; they fly later in the North than in the South."  Chris also provided this map of E. immixta records confirmed by Lafontaine:

Courtesy Chris Schmidt, CNC

(You can see a map with several additional adult sightings here, courtesy of the Moth Photographers Group project.)

Before my finding of this moth at Battle Bluff, what records of it did exist were, of course, records of adult moths.  No one knew what the larva looked like; no one knew what the larva ate.  If the wormwood moth adult were as beloved to people as, say, the monarch butterfly, it would be like knowing and loving the monarch but not knowing that its larva was that delightful yellow-, black-, and white-striped beast that munches merrily away on milkweed plants.

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Needless to say, I am happy to have contributed some basic life history details to our collective human knowledge of the wormwood moth.  It feels all the more special when I consider that Lafontaine identified E. immixta as a moth of relict prairies -- a creature known to dwell in those few tiny remnants of the once vast tallgrass ecosystem that stretched across central North America.  I feel I am, in some way, standing up for these surviving prairies by telling a story of their tiny brown chevron larvae.  I am helping nudge my fellow humans toward an understanding that prairie life matters -- and that, even when it seems like we've almost smudged out that life for good, there are still things about it we have yet to discover.

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NOTES

1. Chris dissected my three adult moths from Battle Bluff in order to make this species determination.

Special thanks to Charley, MJ, Chris, Armund, Terry, and Brad
"View of Battle Bluff from Hwy 35" image obtained from Google Earth Street View