After keeping a constant eye on a clutch of eggs from a rare, subterranean salamander, biologists at Postojna Cave in Slovenia have their reward. Two baby olms have hatched—something that has never been seen outside of a lab, the Christian Science Monitor reports. It's a "rare opportunity for science," the BBC notes, because olms, which eat about once a decade and are thought to live to 100, only reproduce every five to 10 years. (Not to mention that a clutch of 500 eggs may produce just two surviving adults, and a clutch laid in 2013 was eaten by another olm.) "But the challenges are far from over," a press release explains. The olms, which hatched in an aquarium in the cave, will have to be fed and their water will need to be replaced daily to prevent infection.
A female olm laid 64 eggs starting in January; of those, 23 were viable. The first hatchling came on May 30, and the second emerged two days later. "Our first dragon literally shot itself out of the egg in a single attempt," the press release says. (When people first saw them centuries ago, they believed olms were baby dragons, hence the nickname. They are also called "human fish" for their pale, pinkish color.) Nobody witnessed the first hatching, researcher Saso Weldt tells the BBC, but an infrared camera captured the event. "We saw that one was missing," Weldt says. "Then you rewind and suddenly you realize, something has happened." Staff at Postojna Cave hope the rest of the eggs will hatch within weeks. Olms dwell in underground rivers and can grow to be a foot long. Charles Darwin said their undeveloped eyes were an example of natural selection, per the BBC. (Scientists finally classified this "monster" as a vertebrate.)