I was curious as well as I had been using aspen (I live in Florida so the humidity is always high anyway)... But I found wood mites.

Here's the link to my post.
http://ball-pythons.net/forums/showt...best-substrate

i did some research on the repti-zorb liners and decided I'm gonna try it next. Still got aspen for another cage clean or two, but I'm gonna order the liners soon. I'll let you know what I think of them.