We Finally Know Why Millipedes Torment Trains In Japan Every Eight Years


Rachael Funnell

Social Editor and Staff Writer

clockJan 13 2021, 17:13 UTC
Train millipedes obscure the tracks

When the millipede love festival begins, trains don't stand a chance. Photo taken by K. Niijima, CC by 4.0

The curious life cycle of America’s cicadas sees these critters erupt from the ground in their millions every 13 or 17 years, fleetingly filling the air with chattering before falling silent once more. It was thought they were unique in their long lifecycle, but a new study published in the journal Royal Society Open Publishing has uncovered that another creepy crawly elsewhere on the globe has a similar penchant for life under the leaves.

The train millipede, Parafontaria laminata armigera, torments trains in Japan every eight years by obstructing the tracks. Until now, the mechanism behind the peculiar cyclic swarming was unknown. For around half a century, researchers including lead author and government ecologist Keiko Niijima have been studying the species, exposing the bizarre and prolonged development stages of this disruptive arthropod.


Train millipedes lay their eggs in the soil and after they hatch, they must move through seven instar stages before eventually emerging from the soil as a mature millipede eight years later. Each in star stage takes a year, and every summer they molt. Out with the old threads, and in with the new.

In order to confirm the eight-year life cycle of train millipedes, the researchers had to trace their complete life history from egg to adult. They found populations in two locations, and the sites were surveyed several times annually from 1972 to 2016.

seven instar stages
The seven instar stages of Parafontaria laminata armigera. Photo taken by K. Niijima CC by 4.0

By sample the soil at both sites and documenting the changes in the larval millipedes they were able to ascertain that the millipedes go through seven instar changes before reaching maturation. Once mature, they emerge from their molting pouches and swarm on the soil surface. This is when the little tykes become a problem for trains as they emerge in such numbers it obstructs the rail tracks.

Video by K. Niijima CC by 4.0

Some millipedes will travel as far as 50 meters in search of reproductive opportunities. After successfully mating, they will hunker down in the soil again to hibernate over the worst of winter. In late spring, they creep out again for some more mating (what a year!). By July, females will be laying enormous clutches of eggs (from 400 to 1000), eventually popping their clogs (along with the males) a month later.

“We have shown the existence of a periodical millipede, a new addition to periodical organisms with long life cycles: periodical cicadas, bamboos and some plants in the genus Strobilanthes,” wrote the study authors in their paper. “Even though swarming aggregations are very common in many millipedes, e.g. a common millipede Pleuroloma flavipes in the United States, Parafontaria laminata armigera is the first record of periodical non-insect arthropod.”