Ommatoiulus sp.

It is an invasive species in Australia known for its "plagues", when it emerges in swarms so massive that they stop trains, which crush them in huge numbers and make the rails slippery. Like some other millipedes, it produces a secretion with an obnoxious odor and tendency to stain floors when the swarms invade houses.

(http://eol.org/pages/14016/details)