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Japanese Researchers Explain 8-Year Life Cycle Of Train Millipedes


What has dozens of legs, emerges every eight years and can stop a train?


No, this is not a riddle. It is the train millipede, a critter native to Japan and with a surprising life history.

CHANG: In the early 1900s, locals in the mountains west of Tokyo reported swarms of millipedes blocking the tracks of a newly built train line. Biologist Jin Yoshimura says the writhing masses of millipedes likely created an oily, slippery mess.

JIN YOSHIMURA: Later they become very, very slippery. And it was in the high mountains. They have the slope. They're going to go over because of the oil. And then train stops.

KELLY: OK, but here's the strange thing. Japanese train officials noted the same phenomenon nearly every eight years throughout the 20th century.

CHANG: And now Yoshimura's team may know why. They sifted through decades of soil samples, and they determined that the millipedes stay burrowed in the ground for seven years, slowly growing in size.

KELLY: Then eight years after hatching, they burst to the surface, mature adults.

YOSHIMURA: It's time to go out. It's time to go out to find my mate.

KELLY: And then the clock starts over for the next generation. The details are in the journal Royal Society Open Science.

CHANG: Train millipedes are only the second creature in the animal kingdom known to lead such long, periodic lives. Cicadas are the other. Some species go through 13- or 17-year cycles. Doug Yanega of the University of California Riverside says there's a good reason cicadas may do that.

DOUG YANEGA: What they're doing is something that keeps predators and parasites from building up on their populations by overpopulating in certain years and then being absent for long gaps.

KELLY: Whereas millipedes, on the other hand, blast enemies with cyanide when they're attacked. So why the eight-year cycle if not to deter predators?

YANEGA: It's still an open question, and open questions are the kinds of things that attract people's interest.

CHANG: But time may be running out to solve that mystery.

YOSHIMURA: Small swarming we can see, but we don't see any outbreaks anymore.

CHANG: In fact, the last train disruption was in 1984. Yoshimura thinks it might be yet another example of how a warming climate has unexpected effects.

YOSHIMURA: I guess the life cycle is disturbed because of the climactic changes.

KELLY: Climactic changes - meaning we may have cracked the eight-year cycle of the train millipede even though it no longer lives up to the name.

(SOUNDBITE OF MARK BARROTT'S "MOKUSHO") Transcript provided by NPR, Copyright NPR.