Ok. So when I was an uneducated smoker(knew what weed was but not spidermites. Learned that later on.), I had a sack of bud that I forgot about in my firesafe. Not anything special, but regs. When I found it, there were spidermites(didn't know what they were then, but do now) all over. Kinda webs, but more like nests. The majority of the bud(maybe a g) was turned into powder, or shit, idk. Just my experience. I don't see how they could live on dead plant matter, but.....?