Could be humidity beads, what are you using for humidity in the humidor?
do you have kids? If so you might ask them....
It's little pieces of your humidity beads, Daniel. Why would you have to ask, DZR? You're not much of a detective are you?
It's frass. It could be from woodworms or possibly tobacco beetle larvae. I'm not an expert, but that's what I would say. After you clean the entire humidor, see if there's any wood damage.
But seriously, I didn't know that frass existed without it's companion element Sasa. This has just destroyed my world.
I vote frass.
May potentially be frass, from what I see online though it says it would be softer and more powdery if it was. The stuff in the humidor is harder, more like grains of sand. Haven’t totally removed all the boxes yet but can’t find any damage other than a couple missing wooden shelf pins. Not sure why bugs would only eat that type of wood, seems more likely they were missing to begin with.