How low can worms go? According to a new study, at least 0.8 miles (1.3 kilometers) below the Earth's surface.
That's the depth at which scientists discovered a new species of worm, dubbed Halicephalobus mephisto in honor of Faust's demon Mephistopheles. The worm, reported this week in the journal Nature, is the deepest living multicellular organism ever found.
"We tried to get the title of the paper to be 'Worms from Hell,'" said study author Tullis Onstott of Princeton University. "But Nature didn't go for that."
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Onstott and his colleagues have been searching for subsurface life for 15 years, focusing on the ultra-deep mines of South Africa, which penetrate more than 1.8 miles (3 km) into the Earth. They and other teams of scientists have found that life has very deep roots, with single-celled organisms found miles underground. Some of these organisms are quite extreme: One 2008 study found life thriving a mile under the seafloor, surviving in temperatures between 140 and 212 degrees Fahrenheit (60 and 110 degrees Celsius). [Read Extremophiles: World's Weirdest Life]
But finding the multicellular, 0.02-inch-long (0.5 millimeters) H. mephisto is a different story. The worm, or nematode, lives in fluid-filled rock fractures, where it grazes on bacteria, Onstott told LiveScience.
"It's kind of like finding Moby Dick in Lake Ontario," he said. "It's so volumetrically big. It's 10 billion times the size of the bacteria upon which it feeds."
To find the worm, Onstott and his team sampled water from mine boreholes as deep as 2.2 miles (3.6 km). They also sampled soil around the mine boreholes and filtered about 40,000 gallons of surface water to ensure that the nematodes weren't coming into the mine from above.
In the Beatrix gold mine, they found their quarry: the tiny, simple nematode, alive and capable of asexual reproduction. The researchers were able to get H. mephisto to reproduce, and the species is still "squirming around in the lab," Onstott said