We should probably study the characteristics of dens chosen by the various species because this seems to be a pattern. Even though Kooah lived primarly on the left of the split tank, now that she is or is about to brood, she has chosen the same place KaySoh denned on the right side. All my female merc have taken the large purple barnacles (not the same physical set). In the case of my first merc, I did not add the barnacles until several months after she was introduced to the tank but within a week Trapper occupied it. Her daughter moved into her egg home immediately when she was freed from the breeder net at 5 months. Other species, however, don't seem to like the barnacles (and my male mercs would only stay in them temporarily)....oddly enough the same one my first hummelincki chose