In the early 1900s, a train line opened for service in the mountains west of Tokyo. But in 1920, train crews found themselves stopping traffic for an unusual reason. The train tracks, running through dense jungle, were engulfed in swarms of millipedes, all white hinges like ghosts. The creatures, which are not insects and emit cyanide when attacked by a predator, were on a mission that remained mysterious even after they settled in dead leaves and soil.
Trains have resumed service, and millipedes have not been seen again for a long time. But after about a decade, they reappear like spirits rising from the ground, engulfing train tracks and mountain roads again. They seem to follow this pattern over and over again.
Millennium worms fascinated Keiko Nijima, a government scientist who began working in the mountains in the 1970s. During her career, she collected reports of their appearance and coordinated other researchers to collect millipedes throughout their life cycle. A few years ago, I contacted Jin Yoshimura, a mathematical biologist at Japan’s Shizuoka University who studies periodic cicadas. These insects explode to mate and die in massive numbers every 13 or 17 years. She wanted to work with Dr. Yoshimura on the idea that millipedes on the train might be doing something similar.
in this moment A research paper published Wednesday in the Royal Society Open ScienceDr. Niijima, Dr. Yoshimura and Momoka Nii, also from the University of Shizuoka, presented a detailed case that these millipedes, specifically the subspecies Parafontaria laminata armigera, are indeed cyclical, and it is the first time that this behavior has been observed in a non-insect animal, with a life cycle from birth. Until death lasts eight years. However, they also report that millipedes are no longer aggregated in large numbers as before.
Dr. Yoshimura said that when millipede worms rise, they are on their way to new feeding grounds. Mature adults are often spotted on the go; When the creatures reach a new bed of decaying leaves to feed, they eat, mate, lay eggs, and die.
Dr. Niijima and several of her colleagues who reported on the appearance of millipedes carefully collected invertebrates from the soil near where the locust swarms were seen. They hoped to confirm the timescale in which millipedes were evolving – if there were new events each year in the same place, the organisms were unlikely to be cyclical. But if they grow slowly over the years, that will fit the image better.
Over time, it became apparent that not only did they evolve over the course of eight years, but that there were also various groups, or incubators, living in their cycles in separate parts of the mountains. Researchers have identified seven incubators – the event of 1920 was the emergence of the sixth brood, they write, which has been spotted again roughly every eight years since then. The only gap in Brood VI’s record was in 1944, when the turmoil following Japan’s defeat in World War II resulted in no squadrons being registered.
The periodicity of cicadas may have evolved during the period of global cooling to maximize mating opportunities, Dr. Yoshimura and his collaborators have reported. In previous work, With all available adults mixing simultaneously. It is not yet clear what circumstances led millipedes to adopt their strange regularity, although it has been observed that all broods live at relatively high altitudes. Perhaps the extremes of the mountain lifestyle prompted them to repeat.
However, no brood has been seen in many years. Others seem to be shrinking.
“We haven’t seen obstacles on trains in many years,” said Dr. Yoshimura. “Something is changing.”
He suspects that climate change may affect the life cycle of millipedes, indicating that they appear more later in the year than they did before. He also wonders if their diminishing numbers might hinder successful mating, which would accelerate their decline.
“We are still wondering what is the main reason for the decreasing numbers,” he said.