In moist, mossy rooms, rows of glass aquariums bathed in eerie light shelter the last of the last of the frogs.

It is a secure facility, for here reside the sole survivors of their species, rescued from the wild before a modern plague swept through their forests and streams in a ferocious doomsday event that threatens the planet's amphibians with extinction.

The lab smells like a junior-high locker room where the bleach is losing. Perhaps it is all the crickets, larvae, flies — the food that is keeping the frogs alive. They are safe, at least for now, in what scientists are calling an "amphibian ark."

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But time is running out.

The frogs have been captives for five or six years, and frogs do not live forever.

The caretakers hope they will be able to encourage these finicky, exotic, mysterious captives to breed, and then return their progeny — somehow, someday, somewhere — to the wild.

It is much harder than you might think. Because the thing that is killing the frogs is still out there.

In what may be the greatest disease-driven loss of biodiversity in recorded history, hundreds of frog species around the world are facing extinction.

Far from being obscure, many of the frogs threatened at the checkout counter are Class A Number One amphibians — the kinds of jewel-colored frogs that adorn postage stamps and Smithsonian calendars and that biologists consider to be keystone species in their environments, no less important than otters or coral or bees, in their way.

Frogs in the western United States are threatened, and Australia, Europe, Latin America and the Caribbean have been especially hard hit. Central American countries such as Panama are suffering a catastrophic decline.

The villain is a rather extraordinary fungus, an amphibian version of a case of athlete's foot from hell, with an impossible name, Batrachochytrium dendrobatidis, which scientists call "Bd," a virulent, lethal fungus that has spread around the globe.

It is like a cheesy horror movie, but real.

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The little victims? Their pores clog, and they die of a heart attack.

In the pristine tropical forests of the world, the waters still run clear and clean, and the jungle is, as ever, a riot of green, grasping life.

But something is missing.

Where there was once a crazy cacophony of frog song, all day, all night, there is now a spooky quiet.

The streams have gone silent.

The frogs are gone. And they might not be coming back, unless scientists in extinction hot spots such as Panama succeed in their audacious bid to breed the rarest of the rare in captivity in amphibian arks.

In Panama, scientists are returning to sites where just a few years ago they observed frogs in abundance. They are searching for survivors. They are not finding many.

"This sure is depressing," said Cori Richards-Zawacki, a professor from Tulane University who has logged months in the field here.

In rubber boots, carrying a backpack filled with gear to weigh, measure and swab for fungal infection any frog she finds, Richards-Zawacki slogged a few hundred meters down a narrow gorge of the Rio Farallon, peering at the banks covered in moss and fern, water dripping from springs and waterfalls.

It should have been a hopping place. The last time Richards-Zawacki was in this spot, in 2004, she remembers counting 15 golden frogs in two hours, and a number of other diurnal species.

Because Panamanian golden frogs are known as "explosive breeders," a few times a year one could see them congregate by the hundreds at water's edge to copulate.

Today? "Nada. Zero. None," she said.

Scientists calculate that more than a third, and as much as two-thirds, of all frog species in Latin America are at risk.

In Panama, famous for its biological diversity, the country's mascot, the golden frog, has not been seen in the wild since 2008.

Scientists began to document a worldwide decline of amphibians in the 1980s. Many were victims of habitat change, introduced predators, pollution, pesticides or over-harvesting by collectors.

Yet frogs vanished from pristine habitats like those in Panama, where the trees still harbor howler monkeys and pygmy sloths. The contributing causes may include climate change and increased ultraviolet radiation, but one thing is certain: The Bd fungus is wiping out frogs.

"Usually when Bd appears, it kills everything it is going to kill, and quickly," said Roberto Ibanez of the Smithsonian Tropical Research Institute in Panama. "It kills some species, infects others, who serve as disease vectors, as carriers, so it doesn't go away."

Ibanez said the spread of the fungus may have been helped, like other emerging diseases, such as swine flu and AIDS, by globalization.

The fungus may have been spread by the international trade in African clawed frogs, a popular laboratory animal and pet, which was used for pregnancy tests (urine from pregnant women would induce the frog to produce eggs). The clawed frog carries the fungus but does not get sick. The same is true of American bullfrogs.

Studies published in recent months suggest the Bd fungus itself might be evolving, creating a more deadly "superbug." Researches have also found that the more variable the temperature, attributed to climate change, the more lethal the fungus.

In a pretty resort town nestled in the bottom of a volcanic caldera is El Valle Amphibian Conservation Center, known as EVACC, the original Amphibian Ark, supported by the Houston Zoo.

"We knew the fungus would be here, we saw it coming, and we knew we had to do something," said Edgardo Griffith, a founder of the center, who sports a tattoo of a golden frog on his calf.

In 2006 and 2007, Griffith and his team rushed to collect hundreds of frogs, representing a dozen species.

In the beginning, they rented two rooms at the Hotel Campestre, where they would rinse the frogs in an antifungal bath, day after day. They kept the survivors in the quarantine room, before they could be moved to the clean room. "It was a nightmare," Griffith said.

The fungus was already taking its toll.

"I saw frogs dying as we were collecting them. They would die in your hand," Griffith said. "The only option we had was to buy some time, keep them alive."

This is actually the way things are going these days in conservation biology. Some of the most glamorous animals — golden lion tamarinds, red wolves, Siberian tigers — are rebounding from extinction, but many more species are slowly, inexorably being snuffed out.

Scientists aren't sure how long some frog species live, in the wild or captivity, so they are not sure how much time they have. Before they can reintroduce frogs to their home streams, they want to have at least 400 or 500 healthy individuals, for insurance.

For some frog species, they have only a couple of males and females left.

Frogs are sensitive creatures. They drink and respire through their skin. They need just the right amount of ultraviolet light. If they don't get enough vitamin B, they fail to thrive. If they don't get enough calcium, their legs break.

Some frogs prefer fast-moving water, others slow. So the staff turns on and off cloud machines, humidifiers, and shower heads that mimic rainfall.

Three staff members are working 24/7.

Certain frogs fight in their tanks. They punch each other. The staff finds high levels of stress hormones in their feces, and yes — someone is checking.

Encouraging them to breed in small glass fish tanks, made homey with a moist paper towel and a rock or two, is harder than one might think.

Frogs may require the right phase of the moon, or certain bugs, rainfall, songs, or other mysterious clues before they mate. After they reproduce, the hard work continues. Tadpoles are hatching with strange deformities.

"We have to do our job, for a while longer. We have to be successful. Maybe we'll have too many frogs, maybe thousands and thousands. That would be great. But then what are we going to do with them?" said Heidi Ross, director of EVACC.

The hope is that their offspring will soon be returned to the wild, as early as next year. But huge obstacles remain.

"We basically have to become really good frog farmers and breed a lot of frogs, " said Brian Gratwicke, project coordinator for the Panama Amphibian Rescue and Conservation Project at the Smithsonian.

"But the last thing we want to do is release these precious, expensive frogs back into wild, just to see them consumed by the fungus all over again."

Gratwicke hopes his colleagues will find a silver bullet. "But the remedy eludes us," he said.

Some frog species harbor anti-biological agents on their skin that serve as a powerful protection against the fungus. But scientists have not figured out a way to transfer that agent to vulnerable frogs.

There could be a vaccine — someday. Another idea is to challenge captive frogs with the fungus, and select the few that survive, then return their offspring to the wild.

Some individual frogs may have behavior traits that offer them more protection. Frogs that bask in the sun appear to do better, because the fungus does not thrive in high temperatures.

Maybe nature will take its course, and some frog species will make it out in the wild, and others will be lost forever.

"The quiet is incredible," said Jamie Voyles, a scientist at the University of California at Berkeley who was the first to understand the precise mechanism of Bd death.

She is standing in a silent stream in Panama. "I used to collect here, take samples, and it would be please, not another frog! It's 4 a.m. and I want to go home. Now I'm begging them. Come back."