We saw the first pinpricks of light, fireflies sparking in the darkened bushes and shrubs, from the deck above. The four of us—my husband, Greg, myself, and our friends Tiffany and Jason—had been drinking white wine and talking, reveling in the near miracle of a mosquito-free night in Mississippi in late spring. From my seat, I had the best view of the forest floor. “There’s more,” I said as a trio of gleaming bodies floated past. “I see three more.”

We stood up and descended the stairs to the pine-needle-slick trail behind the house. I expected to see a dozen fireflies, perhaps as many as twenty. I grew up in the South and have watched countless fireflies blink across yards like tiny beacons. I usually catch sight of a single insect flickering in the dark and track it, trying to anticipate its lilting trajectory so that I might enjoy the pleasure of seeing it glow anew.

But this was different. We found the woods glittering. The fireflies were everywhere, strung about the understory like hundreds of pure white Christmas lights. They gilded the hillside as far as we could see, down to the moonlit meadow below. In the middle distance, they merged like a river bearing candles on its current. And these fireflies—Photuris frontalis—flamed and dimmed in concert, pulsing in rhythm.

Scientists refer to this pulsing behavior as synchronous. The light show likely plays a role in mating, but like so many other quirks of the natural world, no one really knows for sure. Until that evening, I’d never heard of the phenomenon, and later learned that many people who do know about synchronicity mistakenly believe that it’s limited to a celebrated firefly genus in Asia—Pteroptyx—and a lone species—Photinus carolinus—in Great Smoky Mountains National Park. In reality, North America has a number of synchronous species.

I wondered aloud how many fireflies we could possibly be seeing; it looked as if the night sky had inverted and blanketed the earth with a twinkling galaxy. Jason and Tiffany turned slow circles. They are both population biologists, much better qualified than I am to guess. At least seven hundred, Jason said. Then he decided that estimate was too conservative. More like a thousand.

One thousand bioluminescent bodies on a single hill in a single backyard on the single night we decided to sit outside. Our luck was even greater when you consider that fireflies typically live no more than four weeks as adults, although they must first survive months or perhaps a year in helpless larval form and undergo a wholesale pupal transformation. Then they must coexist in sufficient density before they can set the forest ablaze.

My companions appeared amused enough, but I was elated. I am forty, with a mortgage, a full-time teaching job, and a toddler. My life holds many comforts but few wonders. Lately, I have battled midlife doubts and regrets. Why didn’t we have children earlier, so that we could have more than one? How did my husband and I end up in the Deep South, so far from the granite peaks of California where we fell in love? A year ago, Greg turned down a job offer that would have taken us to Copenhagen—a new country! a new start!—and I have been running over that choice again and again, second-guessing and daydreaming about that alternate life, with its infinite risks and possibilities, that we chose to leave unlived.

“Each step of metamorphosis is fraught with danger,” naturalist Lynn Frierson Faust writes in her field guide Fireflies, Glow-Worms, and Lightning Bugs. “For all of us, fireflies included, it is the transitions of life that are the most dangerous, leaving us naked, exposed, and vulnerable.”

Like seemingly everything wild, fireflies appear to be more vulnerable than ever before. They are victims of habitat loss, pesticides, and light pollution. But they still arrive on semipredictable schedules in much of the eastern United States. They’re especially populous in humid rural and semirural regions like mine, where ample forest litter and darkness prevail. If I pay attention to the temperature and the rainfall and the quality of the local woods—to life around me—I may have the good fortune of seeing them again next year, and in the years that follow.

It’s hard to turn away from a synchronous display, but there are ticks in the woods, and we needed dinner. So we walked back upstairs to the glare of electrical lights in Tiffany and Jason’s dining room and ate a salad of green beans, capers, and hard-boiled eggs. An hour later, I slipped back outside alone.

The night had grown blacker, and it was harder to keep my footing. Frogs called from an adjacent pond. My eyes swept the forest. The cloud of Photuris frontalis still flickered—on, off, on, off—in quick bursts. Years ago researchers showed that synchronous flash patterns are nearly as regular as other cyclic biological activities: the call of the whippoorwill, mindless finger tapping, a human heart during sleep. I felt free of any desire to go elsewhere or be otherwise. I wanted only to stand inside that luminous heart.