Japan's Swarms of Millipedes are Not Random, Research Says they Emerge Every 8 Years
Japan has been experiencing a weird millipede plague along train line for the past eight years. Scientists have now determined that it isn't random and the millipedes swarming the train lines along mountainous regions in Japan have a pattern.
A 50-year-long research project helped them discover more about this species that have been causing trains to halt along their path. It has been revealed that these 3cm to 1.1-inch-long creatures are Parafontaria laminata armigera (P.l.a), a species that has an eight-year life cycle. Apart from this, cicadas are the only species known to have a periodical life span which is so long.
According to their paper, this millipede grows from egg to adult in seven years and then needs one year for maturation. They traced the life history of P.l.a. in two different locations for a complete lifetime.
As noted earlier, study about this millipede began 50 years ago (1972-2016) in the two sites at Mt. Yatsu and Yanagisawa. Ecologist Keiko Niijima led the research. "The soil to a depth of 5 cm was dug out, spread on a polyethylene sheet and the millipedes on the sheet were collected using forceps or an aspirator," he said. Then they repeated procedure at various depths: 5-10cm, 10-15cm and 15-20cm. Everywhere they found millipedes of different of seven different stages or instars. They evidently hibernate in the soil during winter and moult out in the summer. The train millipedes were undergoing the moulting stages every summer.
The adults surface above the soil between September and October. The female of the species lays eggs around August, which can range between 400 to 1,000 in number. Then adults all die then, beginning another 8-year-cycle for the next generation. These generations aren't necessarily in sync with one another, as in the case of cicadas, who all appear simultaneously.
As of now, the researchers suppose that seven different breeds in Central Japan's mountains have completed lifecycle each in different years. Additionally, these animals don't move much. So, train lines along their habitat will see this problem repeated every 8-16 years from each brood. Like a swarm of locusts, they surface in large numbers on the train tracks.
The creature is now the first recorded periodical non-insect arthropod, while there are some bamboos and plants (along with cicadas) that are in the periodical life-form category. Though it is possible that isn't the only one with such a life cycle. Scientists claim that only about a fifth of the world's insects are known and documented and the rest remains a mystery. It is possible to find more periodical insects and arthropods someday.