For more than a century, thousands of poisonous millipedes swarmed the train tracks in Japan’s dense wooded mountains, forcing trains to stop. These “train millipedes”, so called because of their famous obstacles, appeared from time to time – and then disappeared again for years on end. Now, scientists have figured out why.
It turns out that these millipedes (Parafontaria laminata armigera), endemic to Japan, has an unusually long and synchronous life cycle of eight years. These long “periodic” life cycles – in which a population of animals go through life stages at the same time – have only been previously confirmed in some species of cicadas with life cycles of 13 and 17 years, as well as in bamboo and some other plants.
“This millipede is the first non-insect arthropod among all periodic organisms,” said senior author Jin Yoshimura, professor emeritus in the department of mathematics and systems engineering at Shizuoka University in Japan, who has conducted research on periodic cicadas in the past two years. decades.
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Train operators in Japan first observed an outbreak of train millipedes in 1920; they had to stop the train briefly while waiting for the creepy crawlies to pass over the tracks. According to various reports, the millipedes returned every eight years or so after that, each time forming a dense blanket that was impossible to get through. In 1977, the first author Keiko Niijima, a researcher at the Forest and Forest Products Research Institute, proposed for the first time that they could have a periodic cycle of eight years.
Now Niijima, Momoka Nii, also a professor in the mathematical and systems engineering department at Shizuoka University, and Yoshimura have confirmed the life cycle using historical outbreak reports and detailed research. Over many years, the authors collected mountain centipedes in Honshu, Japan, and conducted research on creatures; they determined their life stages by counting the number of legs and body segments, as these are specific to the age of a millipede.
The researchers found that several litters of this population, each with their own synchronization; in other words, one litter may be in the egg stage, while another may be an adult. Each population covers its entire life cycle in eight years.
The litter of millipedes that appears periodically on the train tracks has no affinity with the tracks nor is it intended to be disturbing; instead, the insects are just trying to reach eating areas that are sometimes on the other side of the tracks. It turns out that the railroad is an “obstacle” in its journey to new areas of food, Yoshimura told Live Science. To survive, these train millipedes chew dead or decaying leaves pressed between the ground and fresh leaves on the surface, said Yoshimura.
Because they live in large numbers, adults and seventh nymphs – the stage before they become adults – quickly eat all the food available where they were born; and then they start a journey to move to a new eating place, he said. In this second location, they eat the decaying leaves, mate, lay a batch of new eggs and then die.
The researchers hypothesize that their extended life cycles can be synchronized with winter hibernation. Unlike periodic cicadas that appear in large numbers and therefore make each individual less likely to succumb to predators, these train millipedes do not need that additional protection from predators. They already have a very good defense mechanism: when attacked, they release the poisonous cyanide, the researchers said.
The results were published on January 13 in the newspaper Royal Society Open Science.
Originally published on Live Science.