Re: Woods that are safe for darts and microfauna?
There are many posts here about wood, but possibly searching by the name of the wood you're considering would work best.
I'd like to add a vote for cork bark (not wood, I guess, but close enough). Small flats are great for microfauna hiding spots; rounds are great for everything -- and they double the usable surface area (the outside, and the inside). The texture is quite natural for frogs (rainforests tend not to have a lot of barkless dry wood around...). Takes a lot to make it rot, too.
I think I could turn and live with animals, they are so placid and self-contain'd.