It’s this duality that has ultimately endeared them to us, for these creatures hold out the promise of human transformation, the ability to shed an ugly skin and reveal a hidden self. Part of the appeal of Kermit the Frog is his status as an Everyman: small, far from powerful, but pure of heart. Even his latter-day counterpart Pepe the Frog was originally a good-natured slacker, first drawn in a 2005 comic strip by Matt Furie, before being co-opted as a symbol of the alt-right movement, whose members seem to have conflated Pepe with Kek, the frog-headed Egyptian god representing the darkness before the world was born. (Furie killed off Pepe last year to prevent further misappropriation.)

Another cultural invasion of frogs occurred last winter, when one of the most downloaded smartphone apps in Asia was Tabikaeru (Journey Frog), a game featuring an amphibian that spends much of its time reading in a cozy hut, then wanders off for an indeterminate amount of time, occasionally sending home snapshots. This unfolds without any human input; players do little more than pack food for the frog’s journeys and pine for the little nomad to come back — a comforting inevitability, as kaeru, the Japanese word for frog, sounds almost exactly like the word for return. Tabikaeru is particularly popular in China, where the characters for frog and child are both pronounced “wa” in Mandarin, with only a slight difference in tone.

BUT THESE VIRTUAL FROGS may soon be all we have left. The rate of decline is particularly startling given that, until now, amphibians have outlasted most of life on Earth. “They’re survivors,” says Jennifer B. Pramuk, a herpetologist and animal curator at the Woodland Park Zoo in Seattle, Wash. Their ancestors evolved some 350 million years ago, and they have persisted through three global mass extinctions, including the Permian extinction 251 million years ago, which is known among scientists as the Great Dying because of the number of species lost: an estimated 80 to 96 percent in the oceans and 70 percent on land. Frogs — which separated from salamanders and emerged as a distinct order, Anura, between 240 and 275 million years ago — have been resilient, but their permeable skins are highly sensitive to changes in water quality and temperature.

When we grieve over frogs’ loss and the global degradation it suggests, we’re also mourning a kind of strange, singular natural beauty. Among those now extinct is the golden toad, of which the males were orange-skinned and bright as flame, once prolific breeders in the Monteverde cloud forest of Costa Rica. In 1989, a single male was counted. The next year, there were none. The southern gastric brooding frog, indigenous to the mountains of Queensland in eastern Australia, thrilled herpetologists with its unusual reproductive system: Females swallowed their eggs, which hatched in the stomach, only to be vomited into the world as fully formed froglets. The creature’s final appearance was in 1981.

Conservation efforts have succeeded in reviving a few species. Not long after the Kihansi spray toad, sunny yellow and smaller than a postage stamp, lost its home in the misty wetlands of Tanzania to a hydroelectric dam in 2000, 499 of them were airlifted to the Bronx Zoo. Within three years, only two toads were left at the original Tanzanian site. But by 2010, the rescued toads had spawned a thriving 4,000-strong population at the Bronx Zoo and the Toledo Zoo in Ohio; 2,500 were reintroduced to Tanzania two years later. Zoos may be the key to frogs’ survival, not only nurturing but proselytizing for them, so that a charmed public recognizes their worth.

Without frogs as a predator, mosquitoes and other invertebrates, themselves carriers of disease, will multiply. “It’s another chink in the armor of the ecosystem,” Pramuk says. Gone, too, will be the spring choruses, frogs calling for their mates. Pramuk still remembers when she finally made it to the Costa Rican cloud forest in 1995, six years after the sighting of the last golden toad, one of her favorite species, which she’d studied only on paper. She had hope: Sometimes amphibians thought extinct have suddenly reappeared. “You always think, ‘Maybe it will show itself to me,’” she says. So she stood and waited, listening to the silence. Frogs are the heralds of dusk, their evening song laying the day to rest. Without them, it is only night.

Photographer’s assistant: Garrett Milanovich. Background: Archivart/Alamy