The olm is almost too bizarre to believe. Nicknamed "baby dragon" and "human fish," the cave dweller owes its odd looks to subterranean adaptations like external gills, skin-covered eyes and a long, pale body. If that's not alien enough, it can also live for 100 years, go a decade without food and use electricity to "see" in total darkness.

Olms have lurked deep within parts of Europe for 200 million years, or about 1,000 times longer than our species has been around so far. The spectral cave salamanders were first reported in 1689, when the Slovenian naturalist Janez Vajkard Valvasor understandably mistook them for the offspring of dragons.

Science has since cleared that up, yet olms remain shrouded in mystery centuries later. And despite their long history of evading and confusing us, we now represent one of the species' greatest threats — and possibly one of its best allies.

Given their lengthy life spans, olms take an unhurried approach to romance. In fact, they only breed once or twice a decade, and along with their species' general secrecy, that makes olm eggs an uncommon sight. That's why scientists are so exuberantly nurturing a clutch of 50 to 60 eggs recently laid at a cave in Slovenia.

olm eggOlm eggs take months to develop, and they're highly vulnerable in the meantime. (Photo: Iztok Medja/Postojna Cave)

"It is rare and it is exciting," biologist Sašo Weldt told the New York Times in February, after the eggs were found. "I was jumping when I saw the first one and the second one. It's something you don't want to miss when working as a biologist in a cave."

Postojna Cave dives at least 24 kilometers (15 miles) under Slovenia, carved from limestone over millions of years by the Pivka River. It's a popular tourist destination, thanks to dramatic scenery, native olms and an aquarium built inside the cave, which also contains olms for easier public viewing. That aquarium is where the new olm eggs are located, offering an unusual level of visibility for the shy salamanders.

It's still unclear how many might hatch — or when — but scientists have said three of the eggs are showing signs of growth so far. Here's a recent video of the Postojna mother with her brood, which she has tucked under a flat rock for safety:

Olms are entirely aquatic, unlike most amphibians, and their subterranean lifestyle has allowed their skin to abandon pigment and grow over their eyes. They can still sense some light, but that's nothing compared with their other, weirder senses.

"In place of sight, the olm has developed an acute sensory system for hunting in the dark," explains the Zoological Society of London. "The front part of the olm's head carries sensitive chemo-, mechano- and electroreceptors. Olms have one of the best senses of smell of any amphibian, and are capable of sensing very low concentrations of organic compounds in the water through both smell and taste."

Along with ears specialized to hear underwater, olms' ability to sense electrical and magnetic fields — and to detect subtle chemical cues in water — more than makes up for their undeveloped eyes. And even if all those skills fail to help them find food, they can survive 10 years without a meal. Yet despite such impressive adaptations, 200 million years of evolution may still not have prepared olms for us.

olm at Postojna Cave in SloveniaOlms are Europe's only true cave vertebrates, and the only species in the genus Proteus. (Photo: Jure Makovec/Getty Images)

Scientists don't have enough data to estimate the overall abundance of olms, but due to population declines observed in recent decades, the salamanders are listed as Vulnerable on the IUCN Red List of Endangered Species.

The main threat for olms is transformation of the forests and fields above their caves, according to the IUCN, "largely through tourism, economic changes and increasing water pollution." Such upheaval has a direct effect on the quality of habitat available to olms, which rely on clean water and are susceptible to pollution seeping from the surface. Poaching for the pet trade has also been a persistent danger, even after Slovenia legally protected olms in 1922, but the country's protection mechanisms have reportedly improved since it joined the European Union in 2004.

Postojna Cave in SloveniaPostojna is known as 'the queen of Slovenian caves' — high praise in a country with 11,000 caves. (Photo: Shutterstock)

As rare as olm eggs are, Postojna does have some recent experience. Another female olm graced the cave with eggs in 2013, but some were eaten by predators (including other olms) and the rest failed to hatch. Scientists learned from that failure, however, and are taking extra precautions with the 2016 crop. All olms except the mother have been removed from the tank, the BBC reports, while cave staff are adding extra oxygen to the water and using shades to protect the eggs from light.

"Now it's up to them," Weldt says. Olm eggs develop slowly in multiple stages, which can vary in length based on temperature. If water is 11 degrees Celsius (52 Fahrenheit), the entire process takes at least 120 days. But since these eggs are in roughly 9-degree C (48 F) water, scientists expect them to take even longer.

"The dragons will keep us waiting for a while," the cave's website warns.

Update: As of March 31, the eggs are still healthy and developing normally, according to a press release from Postojna Cave. They survived the particularly dangerous first two months, and are already showing "signs of head, back and tail growth," the release adds.

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.