i've never understood the whole abrasion thing. i typically find tarantulas and other mygs in soil with admixtures of sharp rocks... to the point i get somewhat badly cut digging them out. never seen a spider abraded from this... me yes, spider no. and they typically live amongst the most gods awful spiky plants, too
i somewhat suspect i could actually keep spiders on broken glass and razors and they wouldn't get too cut up. if i made them grossly obese they might have problems... but then it would probably have problems anyways
i use coconut "bark" and i believe aspen bark/shavings to mix with finer ground coconut coir to give better structure and it works great. i have kept terrestrials on just the coconut bark and just some other kind of bark/wood chunks and it was fine
I think its just increased chance of rupture / puncture injury from a fall, as far as abrasiveness goes imho its just long term irratation factor. I mean yea tarantula's live in some rough terrains but if they line their burrows/hides with soft silk and spend most of the day inside their home, concealed from predators and the sun coming out to hunt or pray on the passing by insects during the night. So yea they live in some hell holes but they also make those hell holes homey(i.e. burrow down and web the inside). Personally i never kept any of my T's on wood chips or bark due to the bad stigma that follows that type of substrate in the hobby. I wouldnt immagine a T being able to burrow in bark or chips and i do know that Wood chips esp are a breeding ground for mites.
well... tarantulas and other mygs don't actually stay fully in their burrow, ime. it's not usual to find them inches away and EEEVERY once in a while we find a non mature male individual with no discernible burrow
also, WC definitely do get worn down... but not abraded, ime
but... the thing that confuses me is that typically tarantulas walk on their tip toes as it were. they don't really have a chance to *be* abraded. i guess if you feed them until their belly literally drags it might be an issue... but like i said, i think i could keep them on broken glass and they wouldn't get cut
as for fall damage, that could be the case... but having a tarantula in a cage where you actually have to worry about what the spider can fall onto seems like you are addressing the wrong issue. i guess for arboreals it's kinda par for the course... but we are talking about terrestrials and burrowers, presumably. and in that case... they just plain shouldn't have enough height to fall to have to worry about what they are falling onto.
i only keep terr/burr in high ceiling cages when i don't really care if they live or die over the long term
I am going to flip through TKG tonight i am not sure but i think there is a side note or a picture of a blister, and a paragraph about abrasiveness it either the TKG or the other book i have, its time to break out the reading glasses
IMO because there are other options that are safe and inexpensive, it simply is not worth the additional risk (situational or otherwise) to use bark chips. Coco Coir works beautifully, as does Peat Moss. You needn't worry about a fall with these substrates, as least not in terms of damage caused by the substrate.
It's just not reasonable IMHO to use a substrate that has an increased potential to be damaging when there are others available at or below the same pricepoint.