I have a mature female BN that disappeared 2 or 3 weeks ago. Very little room to hide, I picked up the driftwood and looked everywhere but finally gave up. Thursday morning when I got up she was happy and healthy and clinging to my driftwood. Made a pretty good week for me. I've heard they'll bury themselves in the gravel sometimes but I don't know why, lay eggs? I've got two other BNs that disappeared maybe they'll make a comeback too but I doubt it.