For more than a century, thousands of venomous centipedes have swarmed on train tracks in Japan’s dense forested mountains, forcing trains to stop. These “train millipedes”, so-called because of their known obstacles, would appear to anyone so often – and then disappear again for years. Now scientists have understood why.
It turns out that these millipedes (Parafontaria laminata armigera), endemic to Japan, have an unusually long and synchronous eight-year life cycle. Such long “periodic” life cycles – in which a population of animals moves simultaneously during the life stages – have only been confirmed earlier in some species. cicadas with a 1
“This centipede is the first non-arthropod insect among all periodic organisms,” said senior author Jin Yoshimura, an honorary professor in mathematics and systems engineering at Shizuoka University in Japan who has conducted research on periodic cicadas over the past two decades.
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Train operators in Japan first observed an outbreak of train millipedes in 1920; they had to stop their train for a moment while they waited for the ominous creepers to cross the rails. According to various reports, millipedes returned every eight years or so, each time forming a thick blanket through which it was impossible to pass. In 1977, the first author, Keiko Niijima, a researcher at the Institute for the Study of Forests and Forest Products, first suggested that they could have an eight-year periodic cycle.
Now Niijima, Momoka Nii, also a professor in the Department of Mathematical and Systems Engineering at Shizuoka University, and Yoshimura have confirmed the life cycle using reports from historical foci and detailed studies. For many years, the authors collected millipedes from mountains in Honshu, Japan, and conducted research on the creatures; they determine their stages of life by counting the number of legs and body segments, as they are specific to the age of one milliped.
The researchers found that each set of chickens in this population had its own timing; in other words, one chick may be in the egg phase, while another may be an adult. Each population cycles its entire life cycle in eight years.
The fruit of the centipedes, which periodically appear on the train tracks, has no affinity for the train tracks or is meant to be destructive; rather, the insects are simply trying to reach the feeding grounds, which are sometimes on the other side of the aisles. It so happens that the railway is an “obstacle” in their journey to new places to eat, Yoshimura told Live Science. To survive, these train centipedes feed on dead or decaying leaves enclosed between the soil and fresh leaves on the surface, Yoshimura said.
Because they live in such large numbers, the adult and seventh nymphs – the stage before they become adults – quickly eat up all the food available where they were born; and so they begin the transition to move to a new feeding place, he said. In this second place, they eat the decaying leaves, mate with each other, lay a batch of new eggs and later die.
Researchers suggest that their extended life cycles may be synchronized with winter hibernation. Unlike periodic cicadas, which appear in large numbers and thus make each individual less likely to succumb to predators, these moist centipedes do not need additional protection from predators. They already have a pretty good defense mechanism: when attacked, they release toxic cyanide, the researchers say.
The findings were published on January 13 in the journal Open science of the Royal Society.
Originally published in Live Science.