Every eight years during the fall, a plague of centipedes swarms train lines in mountainous Japan, earning them the nickname ‘train centipedes’.
These small animals (about 3 cm or 1.18 inches long), which play a major role in nitrogen in the larch forests of Japan, have forced trains to stop.
So far, scientists have not been entirely sure what makes them swarm with such peculiar regularity, but a 50-year research project has finally confirmed that the species – Parafontaria laminata armigera (P. la) – exists in a rare life cycle of eight years.
This confirmation is incredibly exciting, as cicadas are the only other known time animals that last that long.
“This centipede needs seven years from egg to adulthood and another year for ripening,” the team wrote in their new article.
“So the eight-year periodicity of P. la was confirmed by tracing the complete life history of eggs to adults in two different places. ‘
We do not know why cicadas emerge at intervals of 13 and 17 years, but thanks to incredible research we understand the life cycle of the train millipedes of eight years.
The train is teeming with millipedes. (Keiko Niijima)
Lead author and government ecologist Keiko Niijima first made observations in these millipedes in 1972, and two main sites were surveyed between one and five times a year for many of the years between 2016 and 2016.
It was quite an operation, and when they arrived at the two sites at Mt. Yatsu and Yanagisawa, the work was not very easy and fast either.
“The soil to a depth of 0–5 cm was excavated, spread on a polyethylene sheet and the millipedes on the sheet were collected using pliers or an aspirator,” the researchers explain.
“Then the same procedure was repeated for depths of 5-10, 10-15 and 15-20 cm.”
When they collected the millipedes they found, they discovered that the millipedes had seven growth stages (called instars), all of which stay in the ground and hibernate in winter and then melt in summer.
“The train millipedes undertake a moult annually in the summer and have seven larval instars,” the researchers write.
“They become adults by the eighth moult after eight years from egg laying.”
(K. Niijima)
Then the adults swarm to the surface in September and October, and they sometimes travel up to 50 meters to get fresh before sleeping during the winter, and copy again in late spring.
By August, the females had laid 400 to 1,000 eggs and the adults were all dead – ready for another eight years.
As with cicadas, the eight years of the millipede are not everywhere together.
The team suspects that there are seven hatcheries in the mountainous region of Central Japan that have completed their life cycle each in different years. That being said, they do not move much, and therefore a specific train line will have the same problem every eight to 16 years.
If we look at historical records dating back to the 1910s, the researchers were able to attribute almost every reported millipede to one of the seven broods.
“We have shown that there is a periodic millipede, a new addition to periodic organisms with long life cycles: periodic cicadas, bamboo and some plants in the genus Strobilanthes, “writes the team.
“Parafontaria laminata armigera is the first record of periodic arthropod non-insects. ‘
With arthropods and insects making up a large percentage of all animals on earth, and only a fifth being identified or named, there will likely still be very long periodic life cycles.
All we have to do is find them.
The research was published in Royal Society Open Science.