I once thought so but my permaculture teacher is saying actually it’s fungal debris from the mother fungus. They are cleaning out the nest and what they are carrying is essentially billions of micro organisms which is why it is such a potent fertiliser, so potent if you give too much to your lettuces for example the nitrogen will burn them. Every day when I walk to the land and I see these guys hard at work I always think of the foundations of Bitcoin, Proof of Work, they epitomise this and remind me to keep my head down, keep working hard with the land, stay humble and stack sats!