I have two that hitchhiked on my Florida live rock. I believe both are Wennerae and are pretty much harmless. They've lived in a 50 gallon with a clownfish, striped blenny, small clown goby, fathead anthias and orchid dottyback for nearly 2 years without issue. My biggest problem with them is that they take out my peppermint shrimp over time so I have to replenish them, but other than that, they are absolutely my favorite hitchhikers. One of them I had taken to hand feeding with some tongs a few times a week which was super cool. He stopped attempting to smash the tongs early on. Unfortunately, I tried remove and rehome him due to the peppermint shrimp thing but he got sucked in to the protein skimmer when I temporarily put him in my sump. I recently discovered that I had a second mantis who is even smaller yet, but similar color and appearance as the first. More reclusive as well. I may trap him and put him in a 10g because he honestly can't be anymore than 1.5" at the most.