Mantis shrimp are kept by people in species only tanks. Its true they have the power to break glass, but it certainly doesn't happen that often. There would have to be a real special set of circumstances for it to do so, like an irresistable treat on the other side of the glass. Some people that keep them in small species only tanks love the little guys, and enjoy feeding and watching them. When I bought my last set of live rock, I found two, one about an inch, the other 3/4 of an inch. I posted about them, and someone on another board offered me 40 bucks for them! They came and picked them up that afternoon, it was amazing. One man's garbage...