I would NEVER use pure perlite. Perlite is puffed silica, i.e. the sugar smacks version of glass without the sugar part. Unless wet to keep it down, the dust off of it is extremely harmful to inhale or get in your eyes - I imagine it would do wonders for tarantula joints and other soft areas. As a minor ingredient in *moist* substrate (e.g. potting soil) I wouldn't consider it much of a risk, but given the choice I would not use it for substrate, or a substrate ingredient.
Hm...that's all I needed to hear..heh... Thanks a mil. I had purchased it for a plant of mine and thought it might be good to use because of the color...it would make my usambra stand out more. I wasn't sure, I knew I had heard about it, but coulnd't remember if it was good or bad. I have seen someone post a pic of sub. that was pure white. Would that be vermiculite by any chance> Would that be alright? THanks for any help and thanks for the help already provided!