My old boss was in the woods showing some ecotourists around and was describing this, and about how half the red millipedes are poisonous (covering their exoskeleton), and the half aren't. She said this as she picked one up to show the group. They asked how she knew the one she picked up wasn't, and she said "I didn't" and then showed them the redness the poison was causing on her hands. She didn't eat it, so it wasn't going to be a real problem, and she'd been in the rainforest enough to know what was going to cause her long term problems and what wasn't.