Depends on how it's used. i would think that walnut shells in a mix w/ peat or potting soil would be fine. But i would not use it by itself as a substrait. The main reason would be that if your using it for a desert scorpion, like a Hairy (H. spadix), i dont think that it would be any good at allowing the scorpion to make a burrow. The Best thing to use would be just strait "play" sand that is wet and packed down then allowed to dry or sand mixed with a small amout of bentonite. I would suggest, if you have not already, go and pick up manny rubio's book published by barron's on scorpions. It talkes quite alot about substrait and housing. Great book on scorpion's ether way. A must have for anyone interested in scorps.