catch him and put him in the sump and feed him once a week. Ive had a 8" peacock mantis is his own species only tank for a year and just recently died to unknown causes. Gave him a emerald crab once a week. From experience nothing is safe it all depends on how he is feeling that day haha. Anything that swims in front of his cave is a potential meal if that mantis is hungry. They are unbelievably smart and fascinating creatures to watch. Mine used to toy with his food hitting the crab, flipping it over then would wait for the crab to turn back over to hit it again because he could control how hard his clubs were hitting the crab. Towards the end of his life I had mine to the point where is knew my face and would come to the front of the tank begging for food and would take food out of my hand the two times I had enough courage to try it hahaha Also had a little red mantis about 1"-2" big that would toy with the big peacock mantis. Watch your hands when you have them in the tank from personal experience getting a 100% power hit from my little red mantis it hurts bad hahaha I was moving some rocks that fell over and totally forgot about my red one, well I didn't forget about him for long when he popped out of a rock and clubbed me! IDK if I've ever moved that fast in my life, I dropped the rock in my hand, pulled my hand out of the tank so fast I sprayed water all over the place and ended up with a bruised, aching swollen finger for 5 days. I have countless videos of mine taking out crabs the best match was the huge gorilla crab that put up a half hour fight to eventually end up like the rest.