@afewbugs I searched around online and there are several articles on lichens growing on bone. E.g., http://sciencythoughts.blogspot.com/2016/09/evidence-of-lichen-growth-on-bones-of.html. But seems to be rarely reported, which might mean that people are just blind to it. Can you post some close-ups? Would also be curious whether the slugs might rip through and cause additional patterning. Very interesting.