Distribution and abundance of 7th instars and swarming adults of a train millipede were investigated in Yatsugatake-Kirigamine area which is most famous area of the outbreak of the millipede. Both 7th instars and swarming adultsof the millipede occurred widely in the area within the range of 1,050 m (a.s.l.) - 1,810 m without any isolation. Densities of the millipede ranged from 11.3 to 928.5m^2 Factors affecting high densities were not known.
The outbreak of Oxidus gracilis (Diplopoda: Polydesmida) happened near Hiraiwa Station, Oito Line, Niigata Prefecture and stopped the special express train `Resort Hakuba Alps' for 2.5 hours on 29 July 2000. The millipedes were swept down from the rail and killed by insecticide. A park was constructed on both sides of the outbreak section three years before. Lawn and redclover with organic fertilizer of the park seemed to provide favorite habitat for the millipede.