Four Wings and a Prayer

by Sue Halpern

  How did the spring leg of the migration work? Back in the nineteenth century, when Charles Riley, the Missouri state entomologist, was pondering the destination of the swarms of monarchs he was seeing each fall, another question was on his mind as well. Riley supposed that the butterflies were heading south, like birds, but then what? Worn, tattered monarchs had been found each spring in the southern United States, but they had merely raised more questions than they answered. Who could know where those butterflies had come from, and when? Even tagging data, when they were later obtained, were inconclusive. How could it be proved that a monarch butterfly tagged in Minnesota in September and found seven months later in Texas, for example, had spent the winter in the Mexican highlands, unless it was recaptured there as well? And the chance of that happening, statistically speaking, was nil.

  Enter—again—Lincoln Brower. While his sometime rival Fred Urquhart was occupied with his tagging project, Professor Brower was in his laboratory at Amherst, continuing the work on chemical defense in monarchs that he had begun as a graduate student at Yale. There he had shown that monarch butterflies were distasteful to birds because of the toxicity of the milkweed they ingested as caterpillars. Now he and his colleagues turned that conclusion on its side and examined it from a different perspective. Since the monarchs stored the toxins—the cardenolides—in their bodies, and since different species of milkweed had different and specific concentrations of the cardenolides, Brower and his colleagues surmised that they should be able to determine which plant or plants a butterfly had eaten in its larval stage. And, they reasoned, since the plants were geographically specific, growing exclusively in some places and not in others, knowing which plants it had eaten as a caterpillar would reveal where that butterfly had come from. They called the process cardenolide fingerprinting. It did have that “the jig is up” quality to it.

  To test their hypothesis, Brower and his associates collected fall migrants, butterflies at the Mexican overwintering colonies, springtime monarchs from Texas, and monarchs found in the northern United States in June. As they suspected, the first group, the fall migrants, had fed on Asclepias syriaca, the big, broad-leaved, common milkweed that grows north of the thirty-fifth parallel. No surprise there. It was the other groups that told them things they could have only guessed before. While both the winter monarchs and the faded ones found in Texas in the spring showed the syriaca pattern, those that had been captured in the North, where syriaca was prevalent, had the fingerprint of two southern milkweeds, viridis and humistrata. To Brower this was “definitive evidence” that the successive-brood theory was right: the migration was a kind of relay race in which fall migrants passed the genetic baton in the spring to offspring whose offspring then continued moving north until they had colonized the entire range and it was time to head south again.

  The evolutionary adaptation that had led to this kind of sequential migration had another interesting feature as well. Viridis and humistrata were both high in cardenolides. The monarchs that carried their fingerprints were extremely toxic to birds, while the ones that carried the syriaca pattern were less so. While this might seem to put the generation that left Mexico at risk, it did not. As these monarchs reached the northern tier, their predators had not yet fledged their own young; by the time that occurred, that generation of monarchs would already have reproduced, and the new generation, born to the southern milkweeds, would take its protection from them.

  AT ABOUT the same time that Bill Calvert was writing from Angangueo that the spring fling had begun, Chip Taylor, sitting in his office at the University of Kansas, was banging out his own assessment. His was based not on firsthand observation but on what he had learned, over years of sorting through the anecdotal information that came his way, of the monarch’s biological clock. This was the same clock that Lincoln Brower had referred to the previous year when he worried that the monarchs’ departure from the overwintering site two weeks early was a sign not of an overeager butterfly population but of habitat destruction that had served as an eviction notice.

  On Tuesday, March 17, Taylor pointed out that “during most seasons, the majority of the monarchs leave the overwintering area during the last two weeks of March. Some pockets of monarchs, perhaps those in the cooler and most protected sites, remain in the overwintering areas through the first week of April. Worn and tattered monarchs should begin appearing in Texas and Louisiana in good numbers in the next four to eight days, weather permitting.” It was a tense and expectant time for monarch watchers, who were waiting to see when, and where, the butterflies would land. It was a time not unlike those few long minutes I remembered from my childhood, when the Apollo astronauts, tumbling to earth, would lose radio contact, and no one would know where they were, we could only imagine them falling, and imagine the heat, but not really know, and then someone would see it, a streak in the sky, and hear a voice against the silence, and the relative safety of an open parachute and finally the arms of the sea, reaching up, snagging it. Four days, eight days, and until then, where?

  Three days after Chip Taylor’s message, Gary Ross, a lepidopterist in Baton Rouge, posted one of his own: “First migrating monarch seen yesterday (3/19/98). It was a male [whose] wings were medium worn.… No others seen.” Another lepidopterist, a young Canadian named Phil Shappert, who was attached to the Stengle—Lost Pines Biological Station near Smithville, Texas, reported finding a worn male a week later. Harlen Aschen, in Victoria, Texas, saw a tattered female around the same time. “No missing parts but seemed exhausted,” he wrote. One after the other, reports like these started coming from Texas and Louisiana, just as Chip Taylor had predicted. If this had been mass transit, it would have had an excellent on-time rating.

  As regularly as the migratory pendulum seemed to swing, the migration itself was different each year. The numbers were different, the pathways were different, the conditions were different. When the monarchs left Mexico two weeks early in 1997, not only were they early, they were ahead of the milkweed, causing some concern that they’d keep flying north until, not finding any, they died. The 1998 exodus adhered to a more typical calendar, though it was curious how the butterflies abandoned their roosts to move down the mountains to form bud colonies at lower elevations. No doubt this had to do with water, which had to do with drought, which had to do with both weather and logging. But the spring of 1998 brought a related concern as well, one suggested by Betty Aridjis’s anguished message from Contepec that past winter: fire.

  “We witnessed many fires burning in forests all over the states of Mexico and Michoacán,” Bill Calvert said in mid-March. “Fires were so frequent and dense that a permanent haze was evident in the sky. None of these were ‘serious’ fires such as the crown fires that we hear about in our northern forests. All were ground fires burning along the forest floors. They created a lot of smoke and, locally, a lot of heat. One such fire was burning near the Chincua colony located in the Arroyo Honda about five kilometers northwest of Angangueo. Although the smoke from this fire was clearly visible, it apparently has not affected the Chincua butterfly colony.”

  Even so, the fires continued to burn all through the spring, some twelve thousand of them, almost all a result of the unhappy collusion of drought and slash-and-burn agriculture, producing smoke that crossed the border and covered parts of the U.S., too. In Mexico City the air rained soot day after day and residents were asked to stay inside with their doors and windows sealed shut. The monarchs, meanwhile, had little choice but to push through this gauntlet of particulates. Like the wind that carried it, smoke was not itself a predator, but for monarchs heading north it might as well have been one.

  FOR THOSE WHO take delight in the sight of a monarch butterfly coursing through the air or dipping into the still of blue asters, the first spring monarch is thrilling. Its now-you-don’t-see-it-now-you-do trick, as it appears suddenly and out of nowhere, too small to have been picked up at a distance like the approaching ducks, and unannounced, unlike the jays and re
dwing blackbirds, can bring you up short. Where I live the first monarch may float in in late May or June, or July at the latest, and claim the black-eyed Susans and goldenrod. Others follow in a desultory way. There may be three in the yard one day, ten the next, then two, then fifteen.

  Following the spring migration over the Internet was efficient, the whole map of the country progressively filling up with dots from bottom to top, each dot representing someone’s story of a particular moment that connected his or her life to the life of a small winged creature. But following it over the Internet was frustrating, too. The monarchs could seem less real than symbolic, an icon of the natural world and its mysteries rather than the mystery itself. “As you wait for the monarch migration to reach your hometown, survey the area for milkweed plants,” Journey North urged readers casting about for something to do. I didn’t have to leave the house. There were a good four inches of crusty snow blanketing the ground. I knew there was milkweed under there, but it had not yet awakened.

  “We are having very strong south winds, with gusts up to thirty-five mph,” Bill Calvert reported from Austin on March 31. “These winds are undoubtedly driving the monarchs north.” For some of us, though, not soon enough.

  The ice went out of the pond two days later, retreating by the hour till the open water glowed like new skin and salamanders came to the surface, only to be caught by my daughter, who had fast hands. “I’m letting you go to see the whole wide world,” she said to one of them, holding it aloft and turning a perfect circle. She had just turned five, and the pond and the ocean of land surrounding our house were her whole wide world.

  On April 12 I surveyed the milkweed again. Nothing doing. The next day I flew down to Texas.

  I think I expected to see scores of monarchs in Texas, faded and worn, the same ones, generationally speaking, that I had seen in the Adirondacks in September and in Mexico two months later. I also expected to see the butterflies in droves, packs of them nectaring and laying eggs, together for the last time before fanning out and dying. I was wrong about that: they didn’t come across the border in swarms and they didn’t gather in groups. The spring migrants were solitary fliers, and though their general destination was known, their touchdown spots were scattered and diverse. To someone hoping to see them, their behavior seemed maddeningly random.

  “SO DID YOU BRING the monarchs?” Bill Calvert asked as I slid into the passenger seat of his reliably cluttered pickup, pushing aside a package of pink hot dogs and a book on the philosophy of science as I did. The Bach tape was still on the dashboard, and maps were piled on the floor, and I knew without turning around that his battered net and makeshift extension pole were wedged in the back behind me. It could have been five months earlier, but for the odometer, Calvert’s superego, which registered all the miles he had logged going back and forth to Mexico.

  “I thought the monarchs were here,” I said, “that’s why I came.”

  Bill Calvert rubbed his mustache and looked amused. “Nope,” he said.

  “Where are they?” I asked. “Farther north?”

  Calvert continued to look amused, maybe because we were in the vicinity of a Luby’s cafeteria. “I’m remembering now,” he drawled, “that you ask good questions.” I was remembering, too: his penchant for answering them with a hapless, almost merry “I don’t know.”

  It was hot in Austin. Bill Calvert was in his trademark jeans and scuffed brown oxfords and a T-shirt. The back of his neck was already deeply rouged by the sun. For me, flying south, the seasons had elided spring, and now it was summer. And somehow, though it was only mid-April, I had missed the monarchs. Calvert, who ran the Texas arm of Monarch Watch, said that most of the reports he was seeing placed the bugs in the northern parts of the state. But even there they were scarce.

  By then we were off the interstate and on a two-lane county road that made the transition from suburb to farmland to scrub desert in less than half an hour. Cattle were grazing and oil pumps nodded like obsequious servants, but all in all it was pretty empty territory. We turned down a wooded driveway marked Masters School, and Calvert stopped the truck. The place was almost deserted except for a lone rooster hopping around its enclosure, making a racket.

  “This is it,” Bill said, making a broad sweep with his arms. His arms opened to a wide, grassy, unshaded field. “This,” he said, “is my study site.”

  I looked around. A couple of buckeye butterflies were ambling through the air, and a red admiral clung to a metal fence. Overhead a purple martin flew by, while a pair of yellow sulfurs mated close to the ground. Calvert was right: no monarchs.

  He got out the hot dogs and his knife and handed them to me. “Cut these up,” he said. “If you don’t mind,” he added. The hot dogs were slimy and warm, and I told him so. “You didn’t think we were going to eat these, did you?” he asked.

  “You’re the guy who gets his vitamin A at Luby’s,” I said, slicing the hot dogs to fit into a container that looked like a medicine vial, the kind that pills come in.

  “OK, here’s the idea,” Bill said conspiratorially. “We’re going to put the hot dogs in the containers.”

  I nodded. This much I had figured out.

  “Then we are going to lay them around each metal enclosure, inside and out.” He pointed to the field. It was dotted with three circular fences, each about fifteen feet across. Inside each enclosure was grass, and milkweed. “We use the hot dogs to see if there are any fire ants here. They’re bait—the hot dogs, not the fire ants. I think the ants are major monarch predators.” We laid down the vials around each circle as if each one were marking off a piece of pie.

  “Now we wait,” Bill Calvert said. “I’m hoping that there will be a preponderance of ants on the outside of the enclosure and virtually none inside.”

  While he waited, Calvert took an inventory of the monarch larvae on the milkweed inside the enclosures, all the while talking into his tape recorder. “Four-inch shoot with nothing on it,” he said. “About two-inch with fifth instar larva and fourth instar. Whoa, there’s another one. I have an asperula, nine inches, with nothing on it. Sixteen-inch with mature buds.”

  When he’d finished inspecting the milkweed inside the fences, he turned to milkweed plants nearby but on the other side of the metal, flipping over each leaf to look for caterpillars.

  He turned to me. “Well, this experiment is working well,” he said. “I only have larvae inside the enclosures.” The alarm on his watch began to beep and he bent over to pick up the first vial, which had been stationed outside the enclosure. “Oh, no,” he said, “this is no good. There aren’t any ants.”

  Calvert moved on, checking each vial in each enclosure and then the ones on the outside. At the second enclosure he held up the first vial. “No ants!” he called. He picked up the second, third, and fourth ones. “No ants!” he called again. “Only one more to go.” He bent down and picked it up and waved it around. It, too, was ant-free. “Now this is what I like to see!” he exclaimed.

  “Oh, no, this isn’t good,” he said a second later. “This is not good.” He was kneeling in the third enclosure, frowning as he watched a gang of ants chew on a chunk of hot dog. Two of the five vials had ants in them. “This is not a good result. We’re just going to have to nuke it,” he said, taking out a foul-smelling poison and spreading it on the ground around the perimeter of the fence. “I hate to use it, but I need an experiment,” he said, distracted for a moment as a single monarch, so worn it was almost translucent, came into range. “There’s your monarch,” he said to me, barely looking up.

  The monarch flew around, it seemed, aimlessly. There were bluebonnets in bloom, and evening primrose, but neither seemed to do it for her. She was three feet off the ground and flapping.

  “Why doesn’t she do something?” I asked Bill Calvert, who looked at me like I was an idiot.

  “What I’m saying is,” I continued, “if it’s the female’s job to get through the winter in order to lay eggs, why is she f
lying around the field and not landing and not laying eggs?”

  Bill Calvert, who was on his knees measuring the milkweed plants, looked up and gave me a big smile that, I have to say, made me feel like less of an idiot.

  “What I’m saying,” he said after a long pause, “is that I don’t know.”

  I TOOK A WALK then and left Bill to his measuring. I watched him from a distance, the scientist at work, crawling around and checking the backs of milkweed leaves for caterpillars. “Got a big one!” he’d call, or “Lots of monarch biomass here!” Calvert was also checking to see which of the two milkweed varieties growing in the field was preferred by monarchs. It was too early to tell, but the results would dovetail nicely with Lincoln Brower’s work on cardenolides. If given a choice, would the monarchs choose the milkweed that would give their offspring more protection? One might expect so, and Bill Calvert was eager to see what would happen. A half hour went by, then another. Calvert kept measuring and talking into his tape recorder. “This really gets exciting right around now,” he called to me as I went over to the truck and tried to figure out a way to sit in its shade without attracting fire ants into my shoes and pants. “Who else would come and spend three hours in the hot sun except someone who is really excited?” he said.