I had three emerald crabs. A couple weeks ago, I found two of them dead in the morning, a couple days apart. There’s plenty of algae and I feed generously, but slowed down on the night feedings directed at the crabs specifically, because of nutrient concerns. I thought they must have starved. the only part of the crabs that seemed to be eaten was the underside of their tail flap thing. I chalked that up to the cuc. Now I’ve realized I haven’t seen one of my hermits, shell or anything in about a week. This is a nano tank (14g) and I only had five hermits to begin with. The missing one had killed a snail and took the shell so he was easy to identify. On two or three occasions, I have heard a sound coming from the tank… sounds like tapping a nail on the tank glass. Not particularly loud. Tap tap.. tap tap tap. I’m not sure that it was the nights before I found the crabs dead. I feel like everyone was still alive the mornings after I heard it. I’ve seen hermits smacking their shell against another, and thought that might be the sound I was hearing, or maybe the hob was doing weird stuff. I’m starting to wonder if I might have a mantis shrimp hiding in here. What are the chances? There are little bits of hermit crab around the tank, but I’ve left a molt in there at least once so i thought those might be from that. I would expect a mantis to do more damage to the emeralds. I also am perplexed about not seeing the hermit shell, the only places I can’t see in this tank are under the sand and inside the rock. The rock is from Petco, and I believe is maricultured, but I’m not sure where.