Dellarobia felt an unaccustomed remove from all the children in terms of nose-wiping and pink-note threats, which were handled by the proficient Miss Rose and two helpers she’d wrangled for the day. Some of the kids knew she was Preston’s mother, but for this field trip she had acquired an aura of special esteem; she was in charge, a teacher-superior kind of personage evidently on par with the principal or Dora the Explorer. Obviously the class had been prepped. Dellarobia had no prior experience in this realm and was struck by their goggle-eyed regard and physical deference. They did not tug unremittingly on her limbs, whine to be carried, or put her outer garments to use as a nose rag. This was quite something, being in charge.

They began their field trip in the lab, where Ovid understandably had safety concerns. His compromise was to allow eight kids at a time just inside the door for a quick lecture while they waited to be shuttled in groups to the top of the High Road. One of the teacher-helpers drove a van. The livestock that shared real estate here with science became an unexpected challenge. Sheep, especially while undertaking their bodily functions, proved vastly more interesting to some than the lab lecture. Ovid was a good sport. “That is biology too,” he said serenely, during a particularly worthy expulsion of methane. Instantly the boys were on his side.

This outing had been all Dellarobia’s idea. She and Ovid had had several well-tempered disagreements about ordinary people mistrusting scientists, and this seemed such a natural starting place, he had to consent. He wasn’t crazy about the interruption, but warmed to the occasion, as he was still the gentle teacher who’d pointed at Preston their first night at supper and declared him a scientist. A moment, Dellarobia now believed, that changed Preston’s life. You never knew which split second might be the zigzag bolt dividing all that went before from everything that comes next. Ovid was patient with their questions about scientists (Do they like to blow up stuff? Could you make a human being?), steering them onto the general butterfly topic. They responded well to any mention of poison. Aposematic coloration was a bright orange butterfly or a wildly striped caterpillar, the bold fellow whose hugely magnified photo was tacked to the wall of the lab. These colors are a stop sign, Ovid explained, warning other creatures not to eat him, or they might very well throw up. Or even die! Dellarobia was touched to see him dressed as she’d never seen him before, in a dress shirt and tie for the kindergartners. Like a slightly more hip Mister Rogers.

From the lab they proceeded to the roost site in a slow-moving swarm, like bees moving with consensus but no strict arrangements from one hive to another. Dr. Byron promised to join them up there to answer more questions at lunchtime, by which Dellarobia hoped he meant in thirty minutes or less. Meanwhile she was to take the reins. The walk from the van to the study site was eventful. In addition to the pine cone war, which devolved to a beetle-throwing contest, there were some warriors down with scraped arms, a good deal more pine sap, and one winter coat utterly, magically gone missing. Lunch boxes fell open everywhere. Three girls felt they saw a bear or a deer, which occasioned some sustained shrieking. None of it threw Miss Rose, their young teacher whose perfectly streaked, flipped hairdo, cool furry boots, and earnest composure conveyed a touching respect for the endeavor of kindergarten. Like Ovid’s tie. Dellarobia felt underdressed, prepared for a regular science day. A small boy in a puffy white jacket like the Michelin Man walked very close to her, constantly picking up the caps of acorns from the trail and handing them over for safekeeping. He was amazingly good at finding them. She probably pocketed thirty in the distance of a hundred yards. He called them “egg corns.” Emboldened by his presence, several girls walked in a little assemblage just behind Dellarobia with an air of the chosen. Their know-it-all leader announced the names of shrubs growing alongside the trail, universally wrong: cabbage, water sprout, hash plant. Where did she get that?

A few children noticed the butterflies as they approached the roost, craning their necks to declaim their astonishment, gathering the whole audience into gasping goshes and wows. Dellarobia heard a few soft curses, probably channeled directly from parents or TV. Butterfly trees, encapsulated branches, prickling trunks: she tried to see it as new, through their eyes. Trees covered with corn flakes. She wished it were one of the magical days when the butterflies swirled like autumn leaves, but being here at all was something for these kids, who seemed unacquainted on principle with the outdoors. Only four had been up here before, two besides Preston and Josefina, though all claimed to have seen it on TV. Today was cold; there was no movement in the trees, and winter had taken its toll. This roost had held upward of fifteen million monarchs, by Ovid’s early estimates, but had suffered about a 60 percent loss, much of that in the last few weeks. Even now they dropped, the pattering sound of little deaths almost continuous. So close to the end, they were literally failing to hang on.

In the little clearing of the study site, the kids settled in a half circle on their sit-upons, which were doubled squares of waterproof fabric stitched together with yarn in anticipation of this very occasion. They had tie-strings and were meant to be worn around the waist like a backward apron, but that didn’t work out, so Miss Rose carried them from the van to be distributed, each to its maker, and at long last sat upon. When asked to give Mrs. Turnbow their full attention, the children’s settling down looked like popcorn in a hot-air popper, but in time the eyes turned up, ready for the zigzag bolt. Dellarobia was nervous, as new to this as any of them, but did her best to tell the story. That the striped caterpillar is also the orange butterfly, not different but the same, just as a baby that becomes a grown-up is still one person, though they look very different. That the forest of butterflies is really all one thing too, the monarch. She explained how the caterpillar eats only one plant, the milkweed, so that is also part of the one big thing. And she told how they fly. Carrying a secret map inside their little bodies, for the longest time content to hang out with their friends, until one day the something inside wakes up and away they go. A thousand miles, which is like light years to a butterfly, to a place they’ve never been. Probably they never even knew they could do that.

At some point Ovid arrived. She sensed some change in the children’s attention and blushed scarlet to realize he’d been behind her, listening. She was finished anyway. Ovid, tall and stunning in his tie and genuine overcoat, not his ordinary field gear, clapped his hands slowly and sincerely for Dellarobia, inciting Miss Rose and the children to do the same. He said he didn’t have much to add, except to mention what was not so good about seeing these butterflies here. Their ordinary home in Mexico was changing, trees getting cut down and climate zones warming up, much too quickly for their liking. He asked the kids if they ever had a big change at home they didn’t like. Every hand went up. Dellarobia envisioned tales of broken transformers or foster care agencies—kids this age could hardly differentiate levels of grief—but Ovid kept to the subject of the wider world and its damage. Animals losing their homes, because of people being a bit careless.