Nearly a decade ago, I Wayan Wardika went back home to Bali on a vacation and found that his village was unrecognizable. Trash choked the river. Synthetic pesticides saturated the rice paddies. And the nights, once alive with the glow of fireflies, had fallen dark.

For generations, the soft glow of the lightning bugs was part of the steady rhythm of nightfall in rural Bali. Today, they are fading, driven away by climate change, aggressive land development for tourism, chemical-intensive farming and artificial light that disrupts their mating rituals.

“We used to have thousands of them illuminating the darkness,” said Mr. Wardika, who grew up in the 1990s, before his village had electricity. “The thought of future generations growing up without experiencing the magic of fireflies, as I did, breaks my heart.”

In Balinese culture, fireflies embody the Tri Hita Karana — the sacred philosophy in which humanity, nature and the divine exist in harmony. This reverence is deeply rooted in local beliefs that these glowing creatures serve as sacred messengers, a connection between living communities and their ancestors.

“They are believed to carry the spirits of ancestors and can guide lost souls,” Mr. Wardika said, explaining that fireflies are considered to be the fingernails of forebears. “My grandmother always scolded me when I caught them and put them in a jar.”

Yet beyond their spiritual charm, these glowing beetles serve as vital ecological messengers. Fireflies typically thrive in pristine, chemical-free environments. Their delicate bodies are acutely sensitive to environmental changes. Their flickering presence signals clean water, healthy soil and minimal light pollution.

Tourism has transformed much of Bali, which is part of Indonesia and where fireflies are no longer as common as they once were.

In 2018, after more than a decade of working as a server on cruise ships, Mr. Wardika moved back to Taro, an ancient village about 20 kilometers, or around 12 miles, north of Ubud, Bali. Converting a corner of his family compound he then founded the Firefly Conservation House, Indonesia’s first firefly conservation facility, which melds Balinese tradition with rigorous science.

A team of biologists at the lab conducts research ranging from field mapping and population counts to controlled rearing and breeding. Researchers build small glass terrariums they call honeymoon suites, a microhabitat designed specifically for courtship. Inside they pair lab-reared females with males caught from the wild, which they say ensures optimal breeding results.

The payoff is not quick. While an adult firefly lives for a brief 22 days, growing one from an egg into a mature beetle takes anywhere from six months to nearly two years, depending on the species.

Day by day, the researchers meticulously track every stage of the beetles’ life cycle from mating and egg-laying through the fragile larval stage. Once mating is complete or the female beetle has reached the end of its natural life, eggs are collected and placed in an incubator to hatch. The terrariums are then sanitized and prepared with soil, for terrestrial species, or water, for the semiaquatic kind, laying the groundwork for the next generation to light up the village night.

The larvae are then isolated — semiaquatic ones in petri dishes and terrestrial ones in individual glass jars. As she often does, Riris Widiari, a biologist, set out to feed row upon row of jars, equipped with a plastic container of chopped fermented worms and a pair of tweezers. Carefully, she lifted the wire mesh off the first container, placed a worm near a larva, secured the mesh and moved to the next.

Ms. Riris, who grew up in a housing complex in Bali, said she had no memory of seeing a firefly as a child. “Now, I am surrounded by them. At the moment, we have more than 1,700 jars,” she said, “and because we leave the lab dark as night falls, the larvae’s teeny glow is noticeable.”

According to the International Union for Conservation of Nature, about a tenth of all assessed firefly species are threatened. Several native Southeast Asian species have been categorized as vulnerable, and a handful are facing extinction. Researchers warn that the true figure of threatened species is likely to be much higher, as there is not enough data on more than half of all firefly species.

In Taro, Mr. Wardika’s group has brought back thousands of larvae into the surrounding controlled area. It has also identified eight native species of firefly.

“It took a lot of trial and error, and many tears to get here,” said Cindy Chayani Mangampang, one of the biologists. “None of us had any idea how to breed fireflies, and there were no local studies to follow.”

Raising fireflies inside the lab is half the battle. To ensure the fireflies have a safe environment to return to, Mr. Wardika encourages local farmers to switch to regenerative organic agriculture. To cut down on chemical use, Mr. Wardika has given out homemade compost, fruit-fermented fertilizer and natural tobacco-based pesticides.

So far, four farms have made the switch. Mr. Wardika’s goal is to enlist 35 farmers across more than 65 acres, creating a two-kilometer, or about 1.2-mile, radius of the lab to be free of synthetic chemicals.

The sanctuary also operates as an eco-tourism destination, which acts as a source of revenue.

On a recent Thursday afternoon, the bustling atmosphere at the center showcased its vital research and education work. Surrounded by floor-to-ceiling shelves stacked with glass jars of larvae, in one corner, Ms. Cindy assisted an intern in harvesting firefly eggs and carefully transferring them to new containers.

A group of tourists gathered around a worktable and listened intently to Ms. Riris’s talk about the firefly’s life cycle, observed different specimens and even used magnifying glasses to search for tiny larvae hidden beneath the leaves of water lettuce.

As darkness fell, excited oohs and ahhs broke out in hushed tones as tiny lights flickered on the ground or occasionally flew deep into the night. Some guests were given glass jars with adult fireflies, which they could release outdoors.

“Fireflies give us the wisdom,” Mr. Wardika said, “to control our actions without disrupting the ecosystem.”