Flat-backed Millipedes

Description:

I spotted four of these large, colorful millipedes within 25 feet of each other along a trail. They were all on top of rotting logs, and all four were dead. Two were completely intact, one was in pieces, and one was headless but otherwise in one piece. All were about 2 inches long, had a yellow and black exoskeleton with orange on the edges, and yellow legs. Millipedes are like the vultures of decaying plant material and other detritus and prefer dark, moist areas such as under logs/leaf litter. I don't usually spot this species, and so it's very unusual for me to spot four at once, especially in such close proximity...and on top of logs since they prefer dark areas. I'm not sure what caused their demise, but I have several theories...1. A fungal infection could have killed them; 2. Predation - although if this was the case, why would two of them be dead, but still intact; 3. Weather - we had heavy rain the previous day. Perhaps they were waterlogged and crawled on the log to dry out and died; 4. Combination of causes - perhaps the rain caused them to climb on top of the logs, and then they died; after which time some were eaten by other critters.... I'm guessing #4 is most likely, but any thoughts or ideas are welcome!

Habitat:

Spotted on rotting logs in a mixed forest.

Notes:

The bright colors exhibited by this species are a warning signal that they secrete cyanide as a defense mechanism. Cyanide is poisonous and can cause extreme irritation if rubbed in the eyes. The millipedes don't contain a massively powerful amount of cyanide and they do not bite, but nevertheless it is recommended that they not be touched or handled in any way for this reason.