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At the time, chytrids were about as obscure as a topic in science can be. Though fungi compose an entire organismal kingdom, on a level with plants or animals, mycology was and largely still is an esoteric field. Plant biologists are practically primetime television stars compared to mycologists. Only a handful of people had even heard of chytrids, and fewer still studied them. There was no inkling back then of the great significance they would later hold.

Longcore happened to know about chytrids because her mentor at the University of Michigan, the great mycologist Fred Sparrow, had studied them. Much yet remained to be learned—just in the course of her doctoral studies, Longcore identified three new species and a new genus—and to someone with a voracious interest in nature, chytrids were appealing. Their evolutionary origins date back 600 million years; though predominantly aquatic, they can be found in just about every moisture-rich environment; their spores propel themselves through water with flagella closely resembling the tails of sperm. Never mind that studying chytrids was, to use Joyce’s own word, “useless,” at least by the usual standards of utility. Chytrids were interesting.

The university gave Joyce an office and a microscope. She went to work: collecting chytrids from ponds and bogs and soils, teaching herself to grow them in cultures, describing them in painstaking detail, mapping their evolutionary trees. She published regularly in mycological journals, adding crumbs to the vast storehouse of human knowledge.

And so it might have continued but for a strange happening at the National Zoo in Washington, D.C., where poison blue dart frogs started dying for no evident reason. The zoo’s pathologists, Don Nichol and Allan Pessier, were baffled. They also happened to notice something odd growing on the dead frogs. A fungus, they suspected, probably aquatic in origin, though not one they recognized. An internet search turned up Longcore as someone who might have some ideas. They sent her a sample which she promptly cultured and characterized as a new genus and species of chytrid: Batrachochytrium dendrobatidis, she named it, or Bd for short.

That particular chytrid would prove to cause a disease more devastating than, as best as scientists can tell, any other in the story of life on Earth. After Longcore’s initial characterization, she and Nichol and Pessier proceeded to show that frogs exposed to Bd died. Other scientists soon linked Bd and its disease, dubbed chytridiomycosis, to massive, inexplicable die-offs of amphibians in Costa Rica, Australia, and the western United States. No disease had ever been known to cause a species to go extinct; as of this writing, chytridiomycosis has driven dozens to extinction, threatens hundreds more, and has been found in more than 500 species.

Almost overnight Longcore went from obscurity to the scientific center of an amphibian apocalypse. “Had I not been studying the ‘useless’ chytrids,” she says, “we wouldn’t have known how to deal with them.” Her research has been crucial—not only the initial characterization, but also her understanding of the systematics and classification of chytrids, which helped provide a conceptual scaffold for questions about Bd: Where did it come from? What made it so strange and so terrible? Why does it affect some species differently than others?