Hawaii was once known for its snails, or kāhuli. Most are smaller than the average garden snail, and far more beautiful. Their shells swirl with the palette of a chocolate box—dark brown, chestnut, white, the occasional splash of mint. Sischo compares them not only to candy but also, because many live in trees, to Christmas ornaments. All of them descended from ancestral mollusks that arrived in Hawaii millions of years ago, perhaps on the bodies of birds. Those stowaways gave rise to more than 750 species—an incredible radiation that turned the snails into exemplars of evolution’s generative prowess.

But in recent decades, kāhuli have come to exemplify the opposite force: extinction. Confined to specific valleys, slow to breed, and inexperienced with predators, they are uniquely vulnerable to the carnivores that have been introduced to Hawaii. Rats and chameleons are serious threats, but their archnemesis is another snail—Euglandina rosea, the aptly named rosy wolf snail. Voracious and fast (for a snail), it tracks its indigenous cousins by following their slime trails, then yanks them from their shells with a serrated tongue or swallows them, shell and all.

Sischo and his five colleagues have been trying to save native snails since 2012, when they expanded a program begun by the University of Hawaii in the 1980s and now run by the state government. In March, when I visited the 44-foot green trailer where they work, Sischo walked me to the back, where dozens of plastic cages are stacked in glass-fronted cabinets the size of refrigerators. He pointed to six cages with purple lids: “These are holding the world population of Achatinella fuscobasis.” Then he gestured to all the cabinets: “This area has 35 species in it.” Each one is already extinct in the wild, or about to be.

Snails may seem low-maintenance, but caring for them is surprisingly hard. Sprinklers regularly mist them to mimic their former forest homes, and the cabinets carefully regulate temperature and humidity. If either variable dips too low, or if the cabinets lose power, Sischo gets barraged by automatic emails and texts. He never silences his phone, even when he sleeps. When he gets alerts at odd hours, his stomach aches.

Sischo is 35, lean, and, despite his work, relentlessly chipper. When he talks about the snails, he is usually stifling laughter that is four parts gallows humor and one part panic. But the panicked portion has been growing. For some reason, already declining snail populations have recently gone into a terminal nosedive. In 2014, for example, Sischo’s team observed a species that hadn’t been seen since the 1980s—seven individuals, in a single tree. It was a hopeful event, but with the trailer still under construction, the team had nowhere to put these survivors. When the conservationists finally returned to rescue the group two years later, they were all gone. “We clipped every freaking leaf on that tree, and nothing,” Sischo said. “That will probably haunt me for the rest of my life.”