Green Pill millipede (Zoosphaerium sp.), Marojejy, Madagascar

Close-up of a pill millipede rolled up into a ball, which they do when threatened. Source of the threat are ants, which you can see on the inner edge of the millipede.

I've based identification on color/appearance, size, and location. The match is likely, but not certain. Literature speaks of Zoosphaerium neptunus as almost always occuring in swarms. I did not notice a swarm, just this one, but I didn't exactly look for more either, and Marojejy is almost impossible to navigate off-path.

If identification is correct, this is the largest pill millipede species in the world. I can confirm that it was quite large, likely making it a female. Males are only half this size.